Neural Control of Human Movement

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CHAPTER 19 Neural Control of Human Movement

CHAPTER OBJECTIVES

➤ Draw the major structural components of the ➤ Outline motor unit facilitation and inhibition and brain, including the four lobes of the cerebral the contribution of each to exercise performance cortex and responsiveness to resistance training ➤ Discuss specific pyramidal and extrapyramidal ➤ Discuss variations in twitch characteristics, resist- tract functions ance to fatigue, and tension development in the different motor unit categories ➤ Diagram the anterior motor neuron and discuss its role in human movement ➤ Describe mechanisms that adjust force of muscle action along the continuum from slight to ➤ Draw and label the basic components of a maximum reflex arc ➤ Define fatigue and discuss factors that act and ➤ Define the terms (1) motor unit, (2) neuromuscular interact to induce neuromuscular fatigue junction, and (3) autonomic nervous system ➤ List and describe functions of the proprioceptors ➤ Summarize the events in motor unit excitation within joints, muscles, and tendons prior to muscle action

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CHAPTER 19 Neural Control of Human Movement 377 The effective application of force during complex learned Brainstem movements (e.g., tennis serve, shot put, golf swing) depends on a series of coordinated neuromuscular patterns, not just on The medulla, pons, and midbrain compose the brain- muscle strength. The neural circuitry in the brain, spinal cord, stem. The medulla, located immediately above the spinal and periphery functions somewhat similar to a sophisticated cord, extends into the pons and serves as a bridge between computer network. In response to changing internal and ex- the two hemispheres of the cerebellum. The midbrain, only ternal stimuli, hundreds of millions of bits of sensory input 1.5 cm long, attaches to the cerebellum and forms a connec- automatically synchronize for near-instantaneous processing tion between the pons and cerebral hemispheres. The mid- by central neural control mechanisms. The input becomes brain contains parts of the extrapyramidal motor system, properly organized, routed, and transmitted with extreme effi- specifically the red nucleus and substantia. The reticular ciency to the effector organs, the skeletal muscles.27 formation integrates various incoming and outgoing signals that flow through it. These signals originate from the stretching of sensors in joints and muscles, from pain recep- NEUROMOTOR SYSTEM tors in the skin, and as visual signals from the eye and audi- ORGANIZATION tory impulses from the ear. Once activated, the reticular system produces either inhibitory or facilitory effects on The human nervous system consists of two major parts: other neurons. Twelve pairs of cranial nerves innervate pre- 1. Central nervous system (CNS) consisting of the dominantly the head region. Each cranial nerve has a name brain and spinal cord and associated number (originally derived by Galen about 2. Peripheral nervous system (PNS) consisting of 1800 years ago). nerves that transmit information to and from the CNS Cerebellum FIGURE 19.1 presents an overview of these two subdivisions. The cerebellum consists of two peach-sized mounds of folded tissue with lateral hemispheres and a central vermis. It Central Nervous System—The Brain functions by means of intricate feedback circuits to monitor Over time the human brain has remained remarkably com- and coordinate other areas of the brain and spinal cord plex, but with selective growth of different anatomic areas. involved in motor control. The cerebellum receives motor From a comparative perspective, the size of the human brain output signals from the central command in the cortex. This exceeds that of most (but not all) mammals. Evolution of the specialized brain tissue also obtains sensory information cortex, particularly the frontal and temporal lobes, coincides from peripheral receptors in muscles, tendons, joints, and skin with unique human functions like spoken and written lan- and from visual, auditory, and vestibular end organs. The guage, reasoning, and abstract thinking. Such differentiation cerebellum functions as the major comparing, evaluating, frames the hypothesis that larger, more complex brains allow and integrating center for postural adjustments, locomotion, greater neural circuitry within the cortex and hence increased maintenance of equilibrium, perceptions of speed of body intellectual and higher center functioning. movement, and other diverse reflex-related movement func- For decades, conventional wisdom maintained that the tions. Movement tasks first learned by trial and error, like number of brain cells was fixed at birth, unlike the cells of other riding a bicycle or swinging a golf club, remain coded as organ systems that continually renew themselves throughout coordinated patterns in the cerebellar memory banks. In life. Neurobiologists now believe that brain cells, spinal neu- essence, this motor control center “fine-tunes” all forms of 29 rons, and neural circuits are created throughout life, with elimi- muscular activity. nation of unneeded or redundant synapses in developing neural tissues. From birth through late adolescence, the brain probably Diencephalon adds billions of new cells, literally constructing new circuits from these newly formed cells.14 After adolescence, the plastic- The diencephalon, located immediately above the ity of neuronal addition and formation of new circuits slows but midbrain, forms part of the cerebral hemispheres. The does not stop, even into old age. Regular physical activity thalamus, hypothalamus, epithalamus, and subthalamus appears to contribute to the development and maintenance of compose the major structures of the diencephalon. The optimal neural circuitry in middle and older age. hypothalamus, situated below the thalamus, regulates FIGURE 19.2 categorizes the brain into six main areas: metabolic rate and body temperature. The hypothalamus medulla oblongata, pons, midbrain, cerebellum, dien- also influences activity of the autonomic nervous system cephalon, and telencephalon. Figure 19.2C depicts four (see p. 382); it receives regulatory input from the thalamus lobes of the cerebral cortex and associated sensory areas. As a and limbic brain system and responds to the effects of di- frame of reference, the body has roughly 10 million sensory verse hormones (see Chapter 20). Changes in arterial blood (afferent) neurons, 50 billion central neurons, and 500,000 pressure and blood gas tensions influence hypothalamic ac- motor (efferent) neurons. This represents a ratio of about 20 tivity via peripheral receptors located in the aortic arch and to 1 between the sensory and motor circuits. carotid arteries. 97818_ch19.qxd 8/4/09 4:16 PM Page 378

Peripheral Central Nervous Nervous Brain System System

So ma ti c se n Skin s o ry f Spinal cord ib er

Visceral s ens ory fiber

Cardio- fiber tor vascular mo ic thet r fiber Sympa oto m Vertebral tic he column pat Parasym

ic at m so f o Muscle er m ib te Spinal nerve r f s to sy Mo us nervo

Nervous System

Central Nervous System (CNS) Peripheral Nervous System (PNS) • Brain (including retinas) • Cranial nerves III—XII • Spinal cord • Spinal nerves • Integrative/control centers

Afferent Division (sensory) Efferent Division (motor) • Somatic and visceral neurons • Motor neurons • Conducts impulses from • Conducts impulses from the receptors to CNS CNS to effectors

Autonomic Nervous System Somatic Nervous System • Involuntary • Voluntary • Conducts impulses from the CNS • Conducts impulses from the CNS to cardiac muscle, smooth to skeletal muscles muscles, and glands

Sympathetic Parasympathetic

Figure 19.1 • The two divisions of the human nervous system. The central nervous system (CNS) contains the brain (including retinas), spinal cord, and integrating and control centers; the cranial nerves and spinal nerves compose the peripheral nervous system (PNS). The PNS further subdivides into the afferent (sensory) and efferent (motor) divisions. The efferent division consists of the somatic nervous system and autonomic nervous system (sympathetic and parasympathetic divisions). 97818_ch19.qxd 8/4/09 4:16 PM Page 379

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Telencephalon Telencephalon Diencephalon The telencephalon contains the two hemispheres of the Thalamus cerebral cortex, including the corpus striatum and medulla. Epithalamus The cerebral cortex makes up approximately 40% of the total brain weight. It divides into four lobes: frontal, temporal, parietal, and occipital. Neurons in the cortex provide specialized sensory and motor functions. Beneath each cerebral hemisphere and in close association with the thalamus lie the basal ganglia, which play an important role in the control of motor movements.

Midbrain Brain Limbic System Pons stem Cerebellum In 1878, French surgeon, neurologist, and anthropologist Medulla oblongata A Paul Pierre Broca (1824Ð1880) described a group of areas on Spinal cord the medial surface of the cerebrum that were distinctly different from the surrounding cortex. Using the Latin word for Longitudinal fissure “border” (limbus), Broca named the area the limbic lobe because its structures formed a ring or border around the brainstem and corpus callosum on the medial surface of the temporal lobe.3 Broca also discovered the speech center now known as Broca’s area, or the third circumvolution of the Motor frontal lobe. Broca should be credited as the founder of mod- cortex ern brain surgery.

Central Nervous System—The Spinal Cord Central Sensory sulcus cortex FIGURE 19.3 illustrates the spinal cord, about 45 cm in length and 1 cm in diameter, encased by 33 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal). The bony vertebral column encases and protects the spinal cord, which attaches to the brainstem. The spinal cord provides the major conduit for the two-way transmission of information from the Left Right hemisphere hemisphere skin, joints, and muscles to the brain. It provides for commu- B nication throughout the body via spinal nerves of the PNS (see p. 382). These nerves exit the cord through small open- ings or notches between the vertebrae. Each spinal nerve con- Motor cortex Sensory cortex nects to the spinal cord by the dorsal root and ventral root Parietal lobe branches. TABLE 19.1 lists common names that describe the Frontal collections of spinal cord neurons and axons. lobe Taste area When viewed in cross section, the spinal cord shows an H-shaped core of gray matter (FIG. 19.4). The ventral (ante- Vestibular area rior) and dorsal (posterior) horns describe the limbs of this Occipital core. The spinal cord core contains principally three types of lobe neurons: motor neurons, sensory neurons, and interneurons. The motor neurons (efferent) run through the ventral Visual area horn to supply the extrafusal and intrafusal skeletal muscle fibers (see p. 393). Sensory (afferent) nerve fibers enter the spinal cord from the periphery by way of the dorsal horn. The white matter, containing the ascending and descending Temporal lobe Cerebellum nerve tracts, surrounds the gray matter within the cord. Auditory C area Ascending Nerve Tracts Figure 19.2 • A. Side (medial) view of the brain and Ascending nerve tracts in the spinal cord forward sen- brainstem. B. Superior view of the brain. C. Four lobes of the sory information from peripheral receptors to the brain for cerebral cortex. 97818_ch19.qxd 8/4/09 4:16 PM Page 380

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Dorsal root Cerebrum Spinal nerve Cerebellum Dorsal root Motor Lower brainstem ganglion unit 2 (medulla) Motor unit 1 Peripheral nerves Impulse Ventral root White matter Gray matter

B Spinal cord ventral view

Spinal cord Vertebral foramen Spinal cord Superior auricular process Spinal nerve

A Spinal column Vertebral body C Cervical vertebra Dorsal gray horn Spinal cord Ventral gray horn Nerve root

Spinal ganglion

Dorsal root Ventral root

Spinal nerve

Gray matter White matter

Intervertebral disc Spinal D Primary spinal cord meninges: structures Pia mater Arachnoid mater Dura mater E Thoracic vertebrae

Figure 19.3 • Human central nervous system anatomy. A. Spinal cord showing the peripheral nerves. B. Ventral view of spinal cord section illustrates dorsal and ventral root neural pathways and nerve impulse direction. C. Cross section through one cervical vertebra. D. Primary spinal cord structures. E. Enlarged view of the junction of three thoracic vertebral bodies. 97818_ch19.qxd 8/4/09 4:16 PM Page 381

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TABLE 19.1 • Common Names Describing Neurons and Axons of the Spinal Cord Name Description/Example

Neurons Gray matter Generic term for a collection of neuronal cell bodies in the CNS (neurons appear gray in a freshly dissected brain) Cortex Collection of neurons forming a thin sheet, usually at the brain’s surface; example: cerebral cortex, the sheet of neurons found just under the surface of the cerebrum Nucleus Distinguishable mass of neurons, usually deep in the brain (not to be confused with the nucleus of a cell); example: lateral geniculate nucleus, a cell group in the brainstem relaying information from the eye to the cerebral cortex Substantia Related neurons deep within the brain, but with less distinct borders than those of nuclei; example: substantia nigra, a brainstem cell group involved in voluntary movement control Locus Small, well-defined group of cells; example: locus coeruleus, a brainstem group of cells involved in control of (plural—loci) wakefulness and behavioral arousal Ganglion From the Greek term for knot; collection of neurons in the peripheral nervous system; example: dorsal root (plural—ganglia) ganglia that contain the cell bodies of sensory axons entering the spinal cord in the dorsal roots; only one cell grouping, the basal ganglia, in the CNS goes by this name; the basal ganglia that lie deep within the cerebrum control movement Axons Nerve A bundle of axons in the peripheral nervous system; the optic nerve is the only collection of CNS axons termed nerve White matter Generic term for a collection of CNS axons (neurons appear white in a freshly dissected brain) Tract Collection of CNS axons having a common site of origin and a common destination; example: corticospinal tract that originates in the cerebral cortex and ends in the spinal cord Bundle Collection of axons running together but not necessarily having the same origin and destination; example: medial forebrain bundle that connects the brainstem with the cerebral cortex Capsule Collection of axons that connect the cerebrum with the brainstem; example: internal capsule that connects the brainstem with the cerebral cortex Commissure Any collection of axons that connect one side of the brain to the other side Lemniscus A tract that meanders through the brain in ribbonlike fashion; example: medial lemniscus that brings tactile information from the spinal cord through the brainstem

From Bear MF, et al. Neuroscience: exploring the brain. 3rd ed. Baltimore: Lippincott Williams & Wilkins, 2006.

processing. Three neurons typically form the sensory path- which contains the third neuron’s cell body. The axon of the way. The dorsal root ganglion contains the cell body of the third neuron passes up to the central command center in the first neuron whose axon relays information into the spinal cerebral cortex. cord. The cell body of the second neuron lies within the Sensory Receptors. Peripheral sensory nerve endings spinal cord itself; its axon passes up the cord to the thalamus, serve as specialized receptors to detect conscious and subconscious sensory information. The “conscious” receptors Pyramidal (lateral) show sensitivity to body position (kinesthesia and propriocep- tract: tion), temperature, and sensations of light, sound, smell, taste, Corticospinal tract touch, and pain. Receptors also monitor subconscious Rubrospinal tract changes in the body’s internal environment; these include chemoreceptors that respond to changes in blood gas tension Extrapyramidal (PO2, PCO2) and pH and baroreceptors that react rapidly to (ventromedial) even small changes in arterial blood pressure. The term tract: Medullary mechanoreceptors generally refers to the sensory receptors reticulospinal tract sensitive to mechanical stimuli of touch, pressure, stretch, and Vestibulospinal tract motion. Tectospinal tract Pontine reticulospinal tract Descending Nerve Tracts Figure 19.4 • Descending spinal cord tracts from the brain. (From Bear MF, et al. Neuroscience: exploring the brain.3rd Axons from the brain move downward through the spinal ed. Baltimore: Lippincott Williams & Wilkins, 2006.) cord along two major pathways displayed in Figure 19.4. The 97818_ch19.qxd 8/4/09 4:16 PM Page 382

382 Section 3 Aerobic Systems of Energy Delivery and Utilization pyramidal tract (lateral tract) activates the skeletal muscula- spinal nerves by mapping the tissues they innervate. This is for- ture in voluntary movement under direct cortical control. The tuitous because an injury to a specific area of the spinal cord other pathway, the extrapyramidal tract (ventromedial produces predictable neurologic damage. tract), controls posture and muscle tone via the brainstem. The peripheral nervous system includes afferent neurons that relay sensory information from receptors in the pe- Pyramidal (Lateral) Tract. Neurons in the pyramidal riphery toward the CNS and efferent neurons that transmit tract (including the corticospinal and rubrospinal tracts) trans- information away from the brain to peripheral tissues. mit impulses downward through the spinal cord. By means of Somatic and autonomic nerves are the two types of efferent direct routes and interconnecting neurons in the cord, these neurons. Somatic nerve fibers (also called motor neurons or nerves eventually excite the alpha (␣) motor neurons that motoneurons) innervate skeletal muscle. Their firing above a control and modulate the fine and gross properties of skeletal threshold level always produces an excitatory response to muscles during all purposeful movements. The corticospinal activate muscle. The autonomic nerves (also called visceral, tract, the longest and one of the largest CNS tracts, has two involuntary, or vegetative nerves) activate cardiac muscle, thirds of its axons originating from the brain’s frontal lobe, sweat and salivary glands, some endocrine glands, and collectively called the motor cortex. smooth muscle cells (also called involuntary muscle) in the intestines and walls of blood vessels. Autonomic activity pro- Extrapyramidal (Ventromedial) Tract. The extrapyra- duces either an excitatory or inhibitory effect depending on midal neurons (reticulospinal, vestibulospinal, and tectospinal the specific neurons activated. tracts) originate in the brainstem and connect at all levels of Whereas tissues of the heart and viscera display consid- the spinal cord. They control posture and provide a continual erable autonomic excitability, conscious control also affects background level of neuromuscular tone. these tissues. For example, individuals who practice yoga or meditation control their heart rate and blood flow “on command.” Such conscious control of the autonomic system has Reticular Formation some application as an alternative treatment in medicine (e.g., The reticular formation provides an extensive and in- gastrointestinal disturbances, hypertension) and to enhance tricate neural network through the core of the brainstem that sports performance (e.g., lower heart rate, steadiness). integrates the spinal cord, cerebral cortex, basal ganglia, and Competitors in archery and biathlon control cardiovascular cerebellum. It receives a continuous flow of sensory data. activity and respiratory movements to temporarily halt the Once activated, it either inhibits or facilitates other neurons. normal breathing cycle and slow heart rate during the crucial For example, the reticular formation helps to control posture “steadiness” phase of the performance (i.e., immediately prior by regulating the sensitivity of neurons to the antigravity to releasing the bowstring or firing the rifle). muscles that maintain upright posture. Excitation of peripheral sensory neurons arouses the reticular nerve cells to Sympathetic and Parasympathetic excite the cerebral cortex. This initiates transmission of sig- Nervous Systems nals back to the reticular system to maintain appropriate cortical arousal and wakefulness. The reticular formation also The autonomic nervous system subdivides into exerts a powerful influence on cardiovascular and pulmonary sympathetic and parasympathetic components. Based on regulation. anatomic and physiologic differences, these neurons operate in parallel but use structurally distinct pathways and differ in their transmitter systems. Figure 16.5 (p. 331) shows that Peripheral Nervous System axons of the sympathetic division emerge only from the middle third of the spinal cord (thoracic and lumbar segments); in The peripheral nervous system contains 31 pairs of spinal contrast, preganglionic axons of the parasympathetic division nerves and 12 pairs of cranial nerves. FIGURE 19.5 shows the emerge only from the brainstem and lowest (sacral) spinal distribution of the 12 pairs of cranial nerves numbered I cord segments. The two systems complement each other through XII. Cranial nerves I and II serve visual and olfactory anatomically. functions and are part of the CNS. Cranial nerves emerge Sympathetic fiber distribution, while displaying some through foramina, or fissures, in the skull (cranium). Cranial overlap with parasympathetic fibers, supplies the heart, nerves, as do their spinal counterparts, contain fibers that trans- smooth muscle, sweat glands, and viscera. Parasympathetic mit sensory and/or motor information. Their neurons innervate nervous system fibers leave the brainstem and sacral segments muscles or glands or transmit impulses from sensory areas into of the spinal cord to supply the thorax, abdomen, and pelvic the brain. The spinal nerves consist of 8 pairs of cervical regions. nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, Regions of the medulla, pons, and diencephalon control 5 pairs of sacral nerves, and 1 pair of coccygeal nerves. A spe- the autonomic nervous system. Fibers that originate in the cific letter and number identifies these nerves (e.g., C-1, first medullary region of the lower brainstem control blood pressure, nerve from the cervical region; T-4, fourth nerve in thoracic heart rate, and pulmonary ventilation, whereas nerve fibers of region). Careful research has traced the exact location of the upper hypothalamic origin regulate body temperature. 97818_ch19.qxd 8/4/09 4:16 PM Page 383

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Oculomotor- CN III Motor: ciliary muscles, sphincter of pupil, all extrinsic muscles of eye except those listed for CN IV and VI

Optic- CN II Optic- CN I Trochlear- CN IV Sensory: vision Sensory: smell Motor: superior oblique muscle of eye CN III CN II CN I

Abducent- CN VI Key Facial- CN VII Motor: lateral rectus Primary root muscle of eye Spinal nerve fibers CN IV Motor: muscles of Efferent (motor) fibers facial expression Afferent (sensory) fibers CN VI

CN VII

CN V CN VII

Trigeminal- CN V Facial- CN VII sensory root Intermediate nerve Sensory: face, sinuses Motor: submandibular, teeth CN VIII sublingual, lacrimal glands Sensory: taste to anterior two thirds of tongue, soft palate

CN V CN XII CN XI CN X CN IX Vestibulocochlear- CN VIII Vestibular nerve, sensory: orientation, motion Trigeminal- CN V Cochlear nerve, sensory: motor root hearing Motor: muscles of mastication

Vagus- CN X Glossopharyngeal- CN IX Motor: larynx, trachea, Motor: stylopharyngeus, Accessory- CN XI parotid gland Hypoglossal- CN XII bronchial tree, heart, Spinal root, motor: GI tract to left colic Sensory: taste: posterior Motor: all intrinsic and sternocleidomastoid flexure one third of tongue; extrinsic muscles of and trapezius Sensory: pharynx, larynx; general sensation: tongue (excluding Cranial root, motor: trachiobronchial tree, pharynx, tonsillar fossa, palatoglossus—a pala- most palatine and lungs, heart, GI tract pharyngotympanic tube, tine muscle) pharyngeal muscles to left colic flexure middle ear cavity

Figure 19.5 • Distribution of the 12 cranial nerves (CN). (From Moore KL, Dalley AF II, eds. Clinically oriented anatomy. 6th ed. Baltimore: Lippincott Williams & Wilkins, 2009.) 97818_ch19.qxd 8/4/09 4:16 PM Page 384

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Reflex Arc

Interneuron Sensory White receptors matter Cell body of sensory neuron Gray Afferent matter Sensory root fiber

Alpha efferent Motor motor neuron root

Cell body of motor neuron

Motor neuron axon

Myelin sheath

Muscle

Fascicles

Nucleus

Muscle fiber Neuromuscular junction

Myofibril Motor unit

Figure 19.6 • Reflex arc showing afferent and efferent neurons plus an interneuron in a spinal cord segment. The darker shaded or gray matter contains the neuron cell bodies; longitudinal columns of nerve fibers make up the white matter. Stimulation of a single ␣-motor neuron activates up to 3000 muscle fibers. The motor neuron and the fibers it innervates collectively constitute the motor unit. The figure shows only one side of the spinal nerve complex.

The Reflex Arc root transmit sensory input from peripheral receptors. These neurons interconnect (synapse) in the cord through interneu- FIGURE 19.6 diagrams the neural arrangement for a typical rons that relay information to different cord levels. The im- reflex arc in one of the 31 spinal cord segments. Afferent pulse then passes over the motor root pathway via anterior neurons that enter the spinal cord through the dorsal (sensory) motor neurons to the effector organ—the muscles. 97818_ch19.qxd 8/4/09 4:16 PM Page 385

CHAPTER 19 Neural Control of Human Movement 385 An example of a reflex is when one suddenly touches a hot object. Stimulation of pain receptors in the fingers trans- Alpha motor mits sensory information over afferent fibers to the spinal neuron cord. This activates efferent motor fibers to elicit an appropriate muscular response (removing the hand rapidly). Muscle Concurrently, the signal transmits through interneuron activity fibers up the cord to sensory areas in the brain, the area that actually Motor “feels” the pain. These various levels of operation for sensory unit input, processing, and motor output, including the reflex action just described, cause removal of the hand from the hot object before the perception of pain. Reflex actions in the spinal cord and other subconscious areas of the CNS control many muscle functions. Literally hundreds of hours of practicing a particular motor task “grooves” the neuromuscular move- A ments to become automatic, no longer requiring conscious control. Unfortunately, improper practice also can automate a Motor task to produce less than optimal neuromuscular actions. Most neuron individuals who practice the golf swing, for example, do so by pool reinforcing poor habits. It starts with the grip and the first 6 inches of the takeaway in the backswing. Setting up with an improper grip, followed by a rapid cocking of the wrists at the start of the backswing, fuels a recipe for disaster (meaning that continual “poor” practice reinforces nonoptimal mechanics). Instead of hitting one ball after another, hours on end, the aspiring golfer should practice correct swing mechanics. The adage “practice makes perfect” should be amended to “perfect Muscle practice makes perfect performance.”

NERVE SUPPLY TO MUSCLE Figure 19.7 • Motor unit and motor neuron pool. A. Motor ␣ One nerve or its terminal branches innervate at least one of unit represents an -motor neuron and the fibers it ␣ the body’s approximately 250 million muscle fibers. The typ- innervates. B. Motor neuron pool represents all the -motor ical individual possesses only about 420,000 motor neurons; neurons that innervate one muscle. thus, a single nerve usually supplies many individual muscle fibers. The number of muscle fibers per motor neuron generally relates to a muscle’s particular movement function. or biceps) (FIG. 19.7). Different motor points exist within the Delicate and precise work of the eye muscles, for example, muscle to allow neural stimulation throughout the muscle’s requires that a neuron control fewer than 10 muscle fibers. length.26 Some motor units contain up to 1000 or more mus- For less complex movements of the large muscle groups, a cle fibers, whereas motor units of the larynx, fingers, or eye- motor neuron may innervate as many as 2000 or 3000 fibers. ball contain relatively few. For example, the first dorsal For muscular activity, the spinal cord is the major processing interosseous muscle of the finger contains 120 motor units and distribution center for motor control. The next sections that control 41,000 fibers; the medial gastrocnemius (calf) examine how information processed in the CNS activates the muscle contains 580 motor units and 1,030,000 muscle fibers. muscles to trigger an appropriate motor response. The average ratio of muscle fibers to motor unit is 340 for the finger muscle and about 1800 for the gastrocnemius muscle. Individual differences in muscle fiberÐmotor unit Motor Unit Anatomy ratios probably contribute significantly to variation in sport The motor unit makes up the functional unit of movement; skill performance. this anatomic unit consists of the anterior motor neuron and the specific muscle fibers it innervates. The individual and The Anterior Motor Neuron combined actions of motor units produce specific muscle actions. Each muscle fiber generally receives input from only The anterior motor neuron illustrated in FIGURE 19.8 consists one neuron, yet a motor neuron may innervate many muscle of a cell body, axon, and dendrites. Its unique design allows fibers because the terminal end of an axon forms numerous transmission of an electrochemical impulse from the spinal branches. Motor neuron pool describes the collection of cord to the muscle. The cell body houses the neuron’s control ␣-motor neurons that innervate a single muscle (e.g., triceps center—the structures involved in replication and transmission 97818_ch19.qxd 8/4/09 4:16 PM Page 386

386 Section 3 Aerobic Systems of Energy Delivery and Utilization

Alpha motor neuron (cell body)

Dendrites Nerve trunk

Axon Bare hillock axon

Direction of propagation of action potential Motor unit Nerve fibers

Node of Ranvier Vein Terminal Motor Artery branches endplate

Impulse

Neurilemma Myelin sheath

Figure 19.8 • The anterior (␣) motor neuron consists of a cell body, axon, and dendrites. Top inset shows a nerve trunk containing numerous individual nerve fibers, including a bare axon. Bottom inset shows a node of Ranvier on the bare axon, which permits impulses to jump from one node to another as the electrical current travels toward the terminal branches at the motor endplate.

of the genetic code. The spinal cord’s gray matter contains the Schwann cell covers the bare axon and then spirals around it, cell body of the motor neuron. The axon extends from the cord sometimes up to 100 times in the biggest fibers. A thinner out- to deliver the impulse to the muscle; dendrites consist of short ermost membrane, the neurilemma, covers the myelin neural branches that receive impulses through numerous con- sheath. The nodes of Ranvier (named for Paris physician and nections and conduct them toward the cell body. Nerve cells histologist Louis Antoine Ranvier [1835Ð1922], who also dis- conduct impulses in one direction only—down the axon, away covered the myelin sheath) interrupt the Schwann cells and from the original stimulation point. myelin every 1 or 2 mm along the axon’s length. Whereas The myelin sheath, a lipoprotein membrane that wraps myelin insulates the axon to the flow of ions, the nodes of around the axon over most of its length, encases larger nerve Ranvier permit depolarization of the axon. This alternating fibers. A large part of this sheath acts as an electrical insulator sequence of myelin sheath and node of Ranvier at about that envelops the axon akin to the plastic coating around 1-mm intervals allows impulses to “jump” from node to node a copper electrical wire. A specialized cell known as a (saltatory conduction) as the electrical current travels toward 97818_ch19.qxd 8/4/09 4:16 PM Page 387

CHAPTER 19 Neural Control of Human Movement 387 the terminal branches at the motor endplate. This type of The terminal portion of the axon below the myelin conduction causes faster transmission velocities in myeli- sheath forms several smaller axon branches whose endings nated fibers compared to unmyelinated fibers. Conduction become the presynaptic terminals. This region possesses speed in a nerve fiber increases in direct proportion to a approximately 50 to 70 ACh-containing vesicles per square fiber’s diameter and thickness of its myelin sheath. Large, micrometer. They lie close to (but do not come in contact myelinated neurons conduct impulses at speeds that exceed with) the muscle fiber’s sarcolemma. The invaginated region 100 m и sϪ1 (224 mph). of the postsynaptic membrane (also called the synaptic Four different nerve fiber groups exist based on size (and gutter) has numerous infoldings that increase the membrane’s thus transmission velocity): surface area. The synaptic cleft between the synaptic gutter and the presynaptic terminal of the axon serves as the region 1. A-alpha (A-␣ [13Ð20 ␮m; 80Ð120 m и sϪ1]) for neural impulse transmission between nerve and muscle 2. A-beta (A-␤ [6Ð12 ␮m; 35Ð75 m и sϪ1]) fiber. 3. A-delta (A-␦ [1Ð5 ␮m; 5Ð35 m и sϪ1]) 4. C-nerve fibers (0.2Ð1.5 ␮m; 0.5Ð2.0 m и sϪ1) Excitation. Excitation normally occurs only at the NMJ. When an impulse arrives at the NMJ, ACh releases from ␣ ␤ ␦ Myelin insulation covers the A- , A- , and A- nerve fibers, saclike vesicles in the terminal axons into the synaptic cleft. while C nerve fibers remain unmyelinated. The thickness of a ACh, which changes a basically electrical neural impulse nerve fiber dictates the speed of neural transmission within into a chemical stimulus, then combines with a transmitterÐ ␣ the fiber—the thickest A- fibers have the fastest transmis- receptor complex in the postsynaptic membrane. The resulting sion speeds, while the smallest C fibers have the slowest change in electrical properties of the postsynaptic membrane transmission speed. These relatively tiny fibers relay informa- elicits an endplate potential that spreads from the motor tion related to pain, temperature, and itch. To give some per- endplate to the extrajunctional sarcolemma of muscle. This spective about the speed of transmission, impulses in C nerve causes an action potential or wave of depolarization to travel fibers travel about 2.2 mph, slower than most people walk. In the length of the muscle fiber, enter the T-tubule system, and ␦ contrast, the A- fibers conduct action potentials at the speed spread to the inner structures of the muscle fiber to prime the ␤ of the winning 100-m Olympic dash, while the A- fibers that contractile machinery for excitation. relay information related to touch travel at speeds close to that The enzyme cholinesterase (concentrated at the borders of most propeller-driver aircraft. As discussed in the section of the junctional folds at the synaptic cleft) degrades ACh ␥ on proprioception, the -efferent fibers connect with special within 5 ms of its release from the synaptic vesicles. ACh hy- stretch sensors in skeletal muscle that detect minute changes drolysis by cholinesterase allows the postsynaptic membrane in muscle fiber length. to repolarize rapidly. The axon resynthesizes the end products All muscle action ultimately depends on three primary of cholinesterase action (acetic acid and choline) to ACh so ␣ sources of input to -motor neurons (motor units): the entire process can begin again when another neural im- 1. Dorsal root ganglion cells with axons that innervate pulse arrives. specialized muscle spindle sensory units embedded Facilitation. ACh release from synaptic vesicles excites within the muscle the postsynaptic membrane of its connecting neuron. This 2. Motor neurons in the brain, primarily in the cerebral changes membrane permeability so sodium ions can diffuse cortex’s precentral gyrus into the stimulated neuron. An action potential generates if 3. Excitatory and inhibitory spinal cord interneurons, the change in transmembrane microvoltage (influx of extra- which make up the largest input cellular sodium and/or efflux of intracellular potassium) Neuromuscular Junction (Motor Endplate). The reaches the threshold for excitation. The term excitatory neuromuscular junction (NMJ) or motor endplate repre- postsynaptic potential (EPSP) describes this change in sents the interface between the end of a myelinated motor membrane potential at the junction between two neurons (FIG. 19.10A). The arrival of a subthreshold EPSP does not neuron and muscle fiber (FIG. 19.9). It transmits the nerve impulse to initiate muscle action. Each skeletal muscle fiber usu- cause the neuron to discharge. Instead, the flow of positive ally contains one NMJ. charges into the cell increases to lower its resting mem- Five common features describe the NMJ:5 brane potential (usually an electrical potential of 65 mV between outside and inside the cell), temporarily increasing its 1. Schwann cells are present. tendency to “fire.” The neuron fires when many subthreshold 2. Terminal section of the neuron contains the neuro- excitatory impulses arrive in rapid succession and the resting transmitter substance acetylcholine (ACh). membrane potential lowers to about 50 mV. Temporal sum- 3. Basement membrane lines the synaptic space. mation describes this condition of repeated subthreshold 4. Membrane across from the synaptic space (the post- stimulation. Simultaneous stimulation of surrounding presy- synaptic membrane) contains ACh receptors. naptic terminals of the same neuron produces spatial sum- 5. Connector microtubules at the postsynaptic mem- mation (and subsequent firing of the muscle fiber). This brane transmit the electrical signal deep within the can induce an action potential from the “summing” of each muscle fiber. individual effect. 97818_ch19.qxd 8/4/09 4:16 PM Page 388

388 Section 3 Aerobic Systems of Energy Delivery and Utilization

Action potential Axon

Sarcolplasm of Synaptic vesicles muscle fiber containing acetylcholine

Mitochondrion Synaptic knob Sarcolemma

Presynaptic membrane T tubule Postsynaptic Sarcoplasmic membrane Neuromuscular reticulum Synaptic cleft junction

Myofibril Ionic concentrations (mM • L–1) across the neuron membrane Ion Extracellular Intracellular Sodium (Na+) 150 15 Chloride (Cl–) 110 10 Potassium (K+) 5 150

Myofilament

Figure 19.9 • Microanatomy of the neuromuscular junction, including details of the presynaptic and postsynaptic contact area between the motor neuron and the muscle fiber it innervates. Inset table shows representative values for ionic concentrations across the motor neuron membrane.

INTEGRATIVE QUESTION Neural facilitation exerts an important influence under special movement conditions. In all-out strength and power Describe neuromuscular factors that help to explain activities, disinhibiting and maximally activating all motor performance differences among individuals who neurons (synchronously) required for a movement becomes devote equal time practicing the volleyball spike. crucial to topflight performance.14,16,24 Enhanced facilitation (disinhibition) leads to full activation of muscle groups during all-out effort and largely accounts for the rapid and The phenomenon of neural facilitation (disinhibition) highly specific strength increases during the early stages of affects neurons within the CNS rather than electrochemical resistance training.9,10,25,28 Chapter 22 discusses the potential events at the NMJ because the NMJ does not release inhibitory for augmenting maximal strength performance through CNS neurotransmitters. Three factors produce neuronal facilitation: facilitation with intense concentration or “psyching.” 1. Decreased sensitivity of the motor neuron to inhibitory neurotransmitters Inhibition.Some presynaptic terminals produce in- 2. Reduced quantity of inhibitory neurotransmitter hibitory impulses. The inhibitory transmitter substance in- substance transported to the motor neuron creases the postsynaptic membrane’s permeability to 3. Combined effect of both mechanisms potassium and chloride ion efflux, thus increasing the cell’s 97818_ch19.qxd 8/4/09 4:16 PM Page 389

CHAPTER 19 Neural Control of Human Movement 389

Impulse

Record Vm Axon

Presynaptic terminal

Postsynaptic dendrite

A Neurotransmitter B molecules

+ + + + Na Na Na Na Cl– Cl– Cl– Cl–

Na+ Na+ Na+ Na+ – – – – Transmitter-gated Cl Cl Cl Cl + ion channels Na Na+ Na+

A B

IPSP

Vm EPSP Vm - 65 mV - 65 mV

0 2468 0 2468 Time from presynaptic action potential (ms) Time from presynaptic action potential (ms)

Figure 19.10 • A. Generation of an excitatory postsynaptic potential (EPSP). An impulse arriving in the presynaptic terminal (top inset) causes neurotransmitter release. The molecules bind to transmitter-gated ion channels in the postsynaptic ϩ membrane. The membrane becomes hyperpolarized when Na enters the postsynaptic cell through the open channels. The EPSP represents the resulting microvoltage change in membrane potential (Vm) recorded by a microelectrode in the cell. B. Generation of an inhibitory postsynaptic potential (IPSP). An impulse arriving in the presynaptic terminal (top inset) causes neurotransmitter release. The molecules bind to transmitter-gated ion channels in the postsynaptic membrane. The membrane Ϫ becomes hyperpolarized if Cl enters the postsynaptic cell through the open channels. The IPSP represents the resulting change in Vm recorded by a microelectrode in the cell. (From Bear MF, et al. Neuroscience: exploring the brain. 3rd ed. Baltimore: Lippincott Williams & Wilkins, 2006.) 97818_ch19.qxd 8/4/09 4:16 PM Page 390

390 Section 3 Aerobic Systems of Energy Delivery and Utilization resting membrane potential to create an inhibitory postsy- (and time to peak force) but remained fatigue resistant, naptic potential (IPSP; Fig. 19.10B). The IPSP hyperpolar- whereas units with higher force capacity shortened rapidly izes the neuron, making it more difficult to fire. A large IPSP but fatigued earlier. FIGURE 19.11 illustrates the major charac- prevents initiation of an action potential when a motor neuron teristics for the three common motor unit categories: receives both excitatory and inhibitory stimulation. For exam- 1. Fast twitch, high force, and fast fatigue (type IIx) ple, one usually can override (inhibit) the reflex to pull the 2. Fast twitch, moderate force, and fatigue resistant hand away when removing a splinter, and so steady the hand (type IIa) to facilitate this unpleasant but necessary task. 3. Slow twitch, low force, and fatigue resistant (type I) The precise neurochemical that provokes an IPSP remains unknown, although ␥-aminobutyric acid (GABA) and the Relatively large motor neurons with fast conduction ve- amino acid glycine exert inhibitory effects. Neural inhibition locities innervate the two major subdivisions of fast-twitch has protective functions and reduces the input of unwanted muscle fibers. These motor units generally contain between stimuli to produce a smooth, purposeful response. 300 and 500 muscle fibers. The fast-fatigable (FF—type IIx) and fast–fatigue-resistant (FR—type IIa) units reach greater peak tension and develop it faster than slow-twitch (S—type I) INTEGRATIVE QUESTION motor units that receive innervation from smaller motor neu- Explain how drugs that mimic neurotransmitters rons with slow conduction velocities. The slower contracting can affect physiologic response and exercise units exhibit more fatigue resistance than the fast-twitch units. performance. Specific exercise training modifies the unique metabolic characteristics of each specific muscle fiber type. With prolonged aerobic training, fast-twitch muscle fibers become almost as fatigue resistant as slow-twitch counterparts (see Chapter 22). MOTOR UNIT FUNCTIONAL Motor neurons themselves have a trophic or stimulating CHARACTERISTICS effect on the muscle fibers they innervate in a way that modu- 8 A motor unit contains only one specific muscle fiber type (type I lates the fibers’ properties and adaptive response to stimuli. or type II) or a subdivision of the type II fiber with the same Surgically innervating fast-twitch muscle fibers with the neuron from a slow-twitch motor unit eventually alters the twitch metabolic profile. TABLE 19.2 classifies motor units based on the following three physiologic and mechanical properties of characteristics of the fast-contracting fibers. Furthermore, the muscle fibers they innervate: application of long-term, low-frequency stimulation to intact fast-twitch motor units induces conversion of the muscle fibers 1. Twitch characteristics to the slow-twitch type.14,22 This neurotrophic effect suggests 2. Tension characteristics that the myoneural junction takes on much greater significance 3. Fatigability than just serving as the site of muscle fiber depolarization. It indicates a remarkable plasticity of skeletal muscle that may Twitch Characteristics indeed be altered through long-term use. Early experiments in motor unit physiology revealed that Tension Characteristics motor units developed high, low, or intermediate tension in response to a single electrical stimulus. Additionally, motor A stimulus strong enough to trigger an action potential in the units with low force capacity exhibited a slow shortening time motor neuron activates all of the accompanying muscle fibers

TABLE 19.2 • Characteristics and Correspondence Between Motor Units and Muscle Fiber Types Force Contraction Fatigue Muscle Fiber Type in Motor Unit Designation Production Speed Resistance Saga the Motor Unit

Fast fatigable (FF—type IIx) High Fast Low Yes Fast glycolytic (FG) Fast—fatigue-resistant (FR—type IIa) Moderate Fast Moderate Yes Fast oxidative glycolytic (FOG) Slow (S—type I) Low Slow High No Slow oxidative (SO)

Modified from Lieber RL. Skeletal muscle structure, function, & plasticity: the physiologic basis of rehabilitation. 3rd ed. Baltimore: Lippincott Williams & Wilkins, 2009. aUnder repetitive stimuli, some motor units respond smoothly with a systematic increase in tension, while others first increase tension and then decrease or “sag” in response to the same tetanic stimulus. These sag characteristics can classify the different motor units. Only the slow motor units do not exhibit sag. This probably relates more to their diminished force-generating capabilities than fatigue characteristics. 97818_ch19.qxd 8/4/09 4:16 PM Page 391

CHAPTER 19 Neural Control of Human Movement 391

•Fast twitch •Fast twitch •Slow twitch •High force •Moderate force •Low force •Fast fatigue •Fatigue resistant •Fatigue resistant Alpha motor neuron (cell body) Twitch 50 40 30 20 20 Force, g Force, 10 10 10

0 g Force, 0 0 100 ms 100 ms 100 ms 200 ms Force, g Force,

Rate of fatigue

100% 100% 100% 0 0 0 046602 046602 046602 Time, min Time, min Time, min

Motor unit Motor unit Motor unit Figure 19.11 • Speed, force, and fatigue characteristics of motor units. “Phasic” motor neurons fire rapidly with short bursts; “tonic” motor neurons fire slowly but continuously.

in the motor unit to contract synchronously. A motor unit higher force requirement progressively enlists more motor does not exert a force gradation—either the impulse elicits an units. Motor unit recruitment describes adding motor units action or it does not. After the neuron fires and the impulse to increase muscle force. As muscle force requirements in- reaches the NMJ, all fibers of the motor unit react simultane- crease, motor neurons are recruited with progressively larger ously. This action embodies the principle of “all or none” axons. This exemplifies the size principle—an anatomic that relates to the normal function of skeletal muscle. basis for the orderly recruitment of specific motor units to produce a smooth muscle action. All of the motor units in a muscle do not fire at the same Gradation of Force time (FIG. 19.12). If they did, it would be virtually impossible The force of muscle action varies from slight to maximal to control muscle force output. Consider the tremendous via two mechanisms: gradation of forces and speeds that muscles generate. When lifting a barbell, for example, specific muscles act to move the 1. Increased number of motor units recruited limb at a particular speed under a set rate of tension develop- 2. Increased frequency of motor unit discharge ment. One can lift a relatively light weight at a number of A muscle generates considerable force when activated speeds. But as weight increases, the speed options decrease by all of its motor units. Repetitive stimuli that reach a muscle accordingly. When lifting a pencil, one generates just enough before it relaxes also increase the total tension. Blending force to lift the pencil regardless of how fast or slowly the arm recruitment of motor units and modification of their firing moves. From the standpoint of neural control, the selective rate permits optimal patterns of neural discharge that allow a recruitment and firing pattern of the fast-twitch and slow- wide variety of graded muscle actions. These range from the twitch motor units that control shoulder, arm, hand, and fin- delicate touch of the eye surgeon to the maximal effort in ger movements (and perhaps other stabilizing regions) throwing a baseball from deep center field on a straight line to provide the mechanism to produce the desired coordinated throw out a runner charging home plate. response. In accordance with the size principle, slow-twitch motor Control of Motor Function and Motor Unit Activity. units with lower thresholds for activation are selectively Low-force muscle actions activate only a few motor units; a recruited during light to moderate effort. Activation of 97818_ch19.qxd 8/4/09 4:16 PM Page 392

392 Section 3 Aerobic Systems of Energy Delivery and Utilization INTEGRATIVE QUESTION Total available motor units Explain how knowledge of neuromuscular exercise physiology can help to enhance an athlete’s (1) strength and power and (2) sports skill performance.

Neuromuscular Fatigue Fatigue represents the decline in muscle tension or force

f active motor units capacity with repeated stimulation or during a given time period. This definition also encompasses perceptual alterations of increased difficulty to achieve a desired submaximal or maximal exercise outcome. Many complex factors produce Number o motor unit fatigue, each relating to specific exercise demands that produce it.1,13,15,17,18 Light Moderate Heavy Voluntary muscle actions exhibit four main components Intensity of effort listed in the following order of nervous system hierarchy: 1. Central nervous system Type IIx Type IIa Type I 2. Peripheral nervous system 3. Neuromuscular junction Figure 19.12 • Recruitment of slow-twitch (type I) and fast- 4. Muscle fiber twitch (type IIa and b) muscle fibers (motor units) in relation to exercise intensity. More intense exercise progressively Fatigue occurs from interrupting the chain of events be- recruits more fast-twitch fibers. tween the CNS and muscle fiber, regardless of the reason. Four examples include: 1. Exercise-induced alterations in levels of CNS neuro- slow-twitch units occurs during sustained jogging or cycling transmitters serotonin, 5-hydroxytryptamine (5-HT), or slow swimming or slowly lifting a relatively light weight. dopamine, and ACh in various brain regions, along More rapid, powerful movements progressively activate with the neuromodulators ammonia and cytokines fast-twitch fatigue-resistant (type IIa) units up through the secreted by immune cells alter one’s psychic or per- fast-twitch fatigable (type IIx) units at peak force. As a runner ceptual state to disrupt ability to exercise.4,19 or cyclist reaches a hill during a distance race, some fast- 2. Reduced glycogen content of the active muscle twitch units become activated to maintain a fairly constant fibers relates to fatigue during prolonged intense pace over varying terrain. Large single muscles with broad exercise.2,7 This “nutrient fatigue” occurs even with origins and/or insertions (like the deltoid), contain smaller, insufficient oxygen available to generate energy dependently controlled “muscles within muscles” that acti- through aerobic pathways. Depletion of phospho- vate depending on the segment’s line of action and direction creatine (PCr) and a decline in total adenine of the intended motion. Such an arrangement allows CNS nucleotide pool (ATP ϩ ADP ϩ AMP) also accom- flexibility to fine-tune skeletal muscle activity to meet the panies the fatigue state in prolonged submaximal demands of the imposed motor task.30 exercise.2 The differential control of motor unit firing patterns rep- 3. Oxygen lack and increased level of blood and mus- resents a major factor that distinguishes skilled from unskilled cle lactate relate to muscle fatigue in short-term, ϩ performances and specific athletic groups.6 Weightlifters maximal exercise. The dramatic increase in [H ] in generally exhibit a synchronous pattern of motor unit firing the active muscle dramatically disrupts the intra- (i.e., many motor units recruited simultaneously during a lift), cellular environment.12,23 Alterations in contractile whereas the firing pattern of endurance athletes is more asyn- function in anaerobic exercise also relate to five chronous (i.e., some motor units fire while others recover). factors: (1) PCr depletion, (2) changes in myosin The synchronous firing of fast-twitch motor units allows ATPase, (3) impaired glycolytic energy transfer the weightlifter to generate force quickly for the desired lift. capacity from reduced activity of the key enzymes In contrast, for the endurance athlete, the asynchronous firing phosphorylase and phosphofructokinase, (4) distur- of predominantly slow-twitch, fatigue-resistant units serves bance in the T-tubule system for transmitting the as a built-in recuperative period so performance can continue impulse throughout the cell, (5) and ionic imbal- ϩ ϩ with minimal fatigue. This occurs because motor units share ances.11 Downregulation in muscle Na , K , and ϩ the burden of multiple movements and intensities during Ca2 release, distribution, and uptake alters the exercise. myofilament activity and impairs muscular 97818_ch19.qxd 8/4/09 4:16 PM Page 393

CHAPTER 19 Neural Control of Human Movement 393 performance,16 even though nerve impulses con- RECEPTORS IN MUSCLES, JOINTS, AND tinue to bombard the muscle fiber. TENDONS: THE PROPRIOCEPTORS 4. Fatigue occurs at the NMJ when an action potential fails to cross from the motor neuron to the muscle Muscles and tendons contain specialized sensory receptors sen- fiber. The precise mechanism for this aspect of sitive to stretch, tension, and pressure. These end organs, “neural fatigue” remains unknown. known as proprioceptors, almost instantaneously relay information about muscular dynamics and limb movement to con- As muscle function changes (often declines) during pro- scious and subconscious portions of the CNS. Proprioception longed submaximal exercise, additional motor-unit recruit- allows continual monitoring of the progress of any sequence of 20 ment maintains the crucial force output necessary to maintain movements and serves to modify subsequent motor behavior. a relatively constant level of performance. During all-out exercise that presumably activates all motor units, a decrease Muscle Spindles in neural activity (as measured by the electromyogram or The muscle spindles provide mechano-sensory information EMG) accompanies fatigue. Reduced neural activity supports about changes in muscle fiber length and tension. They the contention that failure in neural or myoneural transmis- primarily respond to any stretch of a muscle. Through reflex sion produces fatigue in maximal effort. response, they initiate a stronger muscle action to counteract this stretch. INTEGRATIVE QUESTION From a neuromuscular perspective, discuss the Structural Organization

validity of the adage “Perfect practice makes for FIGURE 19.13 shows a fusiform muscle spindle aligned in perfect performance.” parallel to regular muscle fibers or extrafusal fibers. When the muscle stretches, the spindles also stretch. The number of

FOCUS ON RESEARCH Muscular Fatigue: A Complex Phenomenon

Merton PA. Voluntary strength and fatigue. J Physiol recordings of excised muscle from animals (left figure) (Lond) 1954;123:553. that measured muscle tension output of the isolated adductor pollicis that produces thumb adduction. The upper arm ➤ Since the turn of the 20th century, scientists have remained fixed in a flexed position with the hand rotated attempted to explain why repeated maximal muscular ac- outward and stabilized in a grasping position. The arm and tivity produced decreased tension output or fatigue in mus- hand rested in a splint-type device that allowed only thumb cle. The debate over the site of fatigue focuses on the abduction/adduction movement. This hand and arm posi- existence of either a central or peripheral mechanism. tion enabled isolation and recording of muscle tension by Central mechanism refers to a location proximal to the either voluntary muscle action or electrical stimulation via motor neuron (i.e., mainly the brain); a peripheral mecha- the ulnar nerve. nism involves the motor units (i.e., anterior motor neurons, Subjects performed maximal isometric actions to motor endplates, and muscle fibers). Merton reasoned that fatigue. Merton then delivered a series of single twitches he could distinguish central and peripheral mechanisms by evoked by stimulation of the ulnar nerve at approximately inducing fatigue in a muscle group with maximal volun- 12-second intervals preceding and following fatigue. The tary contractions (MVCs) and then stimulating the motor top tracing in the right figure below shows the fatigue unit electrically. “Extra” localized electrical stimulation’s curve for the muscles during the sustained isometric failure to increase force production (i.e., no change in MVC. Tension declined linearly over time, reaching one- fatigue pattern) would indicate a purely peripheral fatigue half its initial value in 1 minute. The lower tracing shows site. In contrast, an increase in muscle tension (i.e., pattern the corresponding action potentials in response to repeated of fatigue decreased) with electrical stimulation would nerve stimulation. Stimulating the motor nerve electrically support a central site hypothesis for muscular fatigue. did not alter the fatigue pattern. Merton reasoned that Merton experimented mainly on himself with an some part of the peripheral apparatus directly affected apparatus modified from one used to measure force fatigue during MVC. Nerve stimulation did not diminish

Continued on page 394 97818_ch19.qxd 8/4/09 4:16 PM Page 394

394 Section 3 Aerobic Systems of Energy Delivery and Utilization

FOCUS ON RESEARCH Continued

the amplitude of the action potential during fatigue (lower tion. Merton’s classic experiments provided the first tracing), so the site of fatigue must have been within the strong support for the role of peripheral factors in muscu- muscle fiber itself rather than at the neuromuscular junc- lar fatigue.

Stimulating electrode Kymograph record

Nerve

Muscle

Time indicator 2.5 k g

Stimulation marker 10 mV

Kymograph Battery

Left. Laboratory apparatus with excised muscle preparation from small animals to record magnitude of muscle action in response to repeated electrical nerve stimulation. Right. Results from modification by Merton of technique on the left on intact muscle of humans to show fatigue curve during sustained isometric maximal voluntary muscle action (top) and corresponding action potentials to repeated electrical stimulation of the motor nerve (bottom).

spindles within a quantity of muscle varies depending on the spiral configuration), entwines about the mid-region of the muscle group. On a relative basis, muscles involved in com- bag fiber. This fiber responds directly to the stretch of the plex movements contain more spindles per gram of muscle spindle; its firing frequency or discharge rate increases in than muscles that perform gross movement patterns. The proportion to the stretch. A second group of smaller sensory spindle, covered by a sheath of connective tissue, contains nerve fibers, the flower-spray endings, makes connections two specialized types of muscle fiber called intrafusal fibers. mainly on the chain fibers but also attaches to the bag fibers. One type of intrafusal fiber, the fairly large nuclear bag These endings show less sensitivity to stretch than annu- fiber, contains numerous nuclei packed centrally through its lospiral fibers. Activation of the annulospiral and flower- diameter. Each spindle usually contains two nuclear bag spray sensors relays impulses through the dorsal root into fibers. The other type of intrafusal fiber, the nuclear chain the cord to produce reflex activation of the motor neurons to fiber, contains many nuclei along its length. These fibers the stretched muscle. This causes the muscle to act more attach to the surface of the longer nuclear bag fibers. Each forcefully and shorten, which reduces the stretch stimulus spindle usually contains four to five chain fibers. The ends of from the spindles. the intrafusal fibers contain actin and myosin filaments and The third type of spindle nerve fiber, the thin ␥-efferent exhibit shortening capability. fiber that innervates the contractile, striated ends of the Two sensory afferent fibers and one motor efferent intrafusal fibers, serves a motor function. Higher centers in fiber innervate the spindles. A primary afferent nerve fiber, the brain activate these fibers to maintain optimal sensitivity the annulospiral nerve fiber (composed of a set of rings in of the spindle at all muscle lengths. Regardless of the muscle’s 97818_ch19.qxd 8/4/09 4:16 PM Page 395

CHAPTER 19 Neural Control of Human Movement 395

Gamma motor Sensory efferents afferents

Primary afferent Secondary afferent annulospiral ending flower spray

Muscle spindle Capsule Intracapsular Nuclear Nuclear space bag fiber chain fiber

Figure 19.13 • Structural organization of the muscle spindle with an enlarged view of the equatorial region of the spindle.

overall length, ␥-efferent stimulation activates the intrafusal involves only one synapse (monosynaptic). The spindles lie fibers to regulate their length and sensitivity. This mechanism parallel to the extrafusal fibers so they stretch when these prepares the spindle for other lengthening actions, even when fibers elongate as the hammer strikes the patellar tendon. the muscle remains shortened. Adjustments in ␥-efferent The spindle’s sensory receptors fire when its intrafusal fibers activation allow the spindle to continuously monitor the length stretch. This directs impulses through the dorsal root into the of the muscles that contain them. spinal cord to directly activate the anterior motor neurons. The gray matter contains neuron cell bodies; the white matter carries longitudinal columns of nerve fibers. Stimulation The Stretch Reflex of a single ␣-motor neuron affects up to 3000 muscle fibers. The muscle spindle detects, responds to, and modulates The reflex also activates interneurons within the cord to changes in the length of the extrafusal muscle fibers. This facilitate the appropriate motor response. For example, exci- provides an important regulatory function for movement and tatory impulses activate synergistic muscles that support the maintenance of posture. Postural muscles continuously desired movement, while inhibitory impulses flow to motor receive neural input to sustain their readiness to respond to units that normally counter the movement. In this way, the conscious (voluntary) movements. These muscles require stretch reflex acts as a self-regulating, compensating mecha- continual subconscious activity to adjust to the pull of grav- nism. This salient feature allows the muscle to adjust auto- ity in upright posture. Without this monitoring and feedback matically to differences in load (and length) without mechanism, the body would literally collapse into a heap requiring immediate information processing through higher from the absence of tension in neck muscles, spinal muscles, CNS centers. hip flexors, abdominal muscles, and large leg musculature. To this end, the stretch reflex provides a fundamental controlling mechanism. Golgi Tendon Organs Three main components make up the stretch reflex: In contrast to the muscle spindles that lie parallel to the 1. Muscle spindle that responds to stretch extrafusal muscle fibers, the Golgi tendon organs (first iden- 2. Afferent nerve fiber that carries the sensory impulse tified in 1898 by Italian physician Camillo Golgi (1843Ð1926) from the spindle to the spinal cord and named in honor of him) connect to up to 25 extrafusal 3. Efferent spinal cord motor neuron that activates the fibers near the tendon’s junction to the muscle. These fine- stretched muscle fibers tuned sensory receptors detect differences in the tension FIGURE 19.14 illustrates the patellar tendon stretch reflex generated by active muscle rather than muscle length. (knee-jerk reflex), the simplest autonomic reflex arc that FIGURE 19.15 shows that the Golgi tendon organs respond as 97818_ch19.qxd 8/4/09 4:16 PM Page 396

396 Section 3 Aerobic Systems of Energy Delivery and Utilization

Dorsal horn Ventral horn White matter Gray Sensory neuron matter (afferent fiber)

Muscle spindle Extensor muscles Alpha Synapse motor neuron (efferent fiber)

Tendon

Leg extension

Figure 19.14 • The patella tendon stretch reflex (shows only one side of the spinal nerve complex).

a feedback monitor to discharge impulses under either of muscle and surrounding connective tissue harness from injury two conditions: from sudden or excessive load. 1. Tension created in the muscle when it shortens 2. Tension when the muscle stretches passively Pacinian Corpuscles When stimulated by excessive tension, the Golgi recep- Pacinian corpuscles are small, ellipsoidal bodies located tors transmit signals to the spinal cord to elicit reflex inhibi- close to the Golgi tendon organs and embedded in a single, tion of the muscles they supply. This occurs from the unmyelinated nerve fiber. These sensitive sensory receptors overriding influence of the inhibitory spinal interneuron on respond to quick movement and deep pressure. Deformation the motor neurons supplying the muscle. Consider Golgi ten- or compression of the onionlike capsule by a mechanical don organs as a protective sensory mechanism much like a stimulus transmits pressure to the sensory nerve ending “governor” mechanism that sets the speed limit for motorized within its core to change the electric potential of the sensory go-carts. Excessive change in muscle tension increases the nerve ending. If this generator potential achieves sufficient Golgi sensor’s discharge to depress motor neuron activity and magnitude, a sensory signal propagates down the myelinated reduces force output. Golgi receptors remain relatively inac- axon that leaves the corpuscle and enters the spinal cord. tive and exert little influence if muscle action produces little Pacinian corpuscles act as fast-adapting mechanical sen- tension. Ultimately, the Golgi tendon organs protect the sors. They discharge a few impulses at the onset of a steady 97818_ch19.qxd 8/4/09 4:16 PM Page 397

CHAPTER 19 Neural Control of Human Movement 397

IN A PRACTICAL SENSE How to Determine Upper-Arm Muscle and Fat

Girth measurements include bone surrounded by a mass of muscle 2. Arm muscle area, cm2 ϭ Ϫ ␲ Ϭ ␲ tissue ringed by a layer of subcutaneous fat (Fig. A). Muscle repre- [Garm ( Sftri)] 4 sents the largest component of girth (except in obese and elderly ϭ (30.0 cm) Ϫ (␲2.5 dm)2 Ϭ 4␲ persons), so girth indicates one’s relative muscularity. The proce- ϭ 488.4 Ϭ12.566 dure for estimating limb muscle area assumes similarity between a ϭ 38.9 cm2 limb and a cylinder, with subcutaneous fat evenly distributed 3. Arm area (A), cm2 ϭ 2 Ϭ ␲ around the cylinder (Fig. A). (Garm) 4 ϭ (30.0 cm)2 Ϭ 4␲ MEASUREMENTS ϭ 900 Ϭ 12.566 ϭ 2 Determine the following: 71.6 cm 2 1. Upper-arm girth (relaxed triceps; G ): Measure with arm 4. Arm fat area, cm arm ϭ Ϫ extended relaxed at the side (or parallel to the ground in an arm area arm muscle area ϭ 2 Ϫ 2 abducted position). Measure girth (cm) midway between the 71.6 cm 38.9 cm ϭ 2 acromial and olecranon process (Fig. B). 32.7 cm 5. Arm fat index, % fat area 2. Triceps skinfold (Sf ): Measure in decimeters (dm; mm Ϭ 10) on tri ϭ (arm fat area Ϭ arm area) ϫ 100 the back of the arm over the triceps muscle as a vertical fold at ϭ (32.7 cm2 Ϭ 71.6) ϫ 100 the same level as the relaxed arm girth (Fig. C). ϭ 45.7% EXAMPLE ϭ ϭ Data: Upper-arm girth (Garm) in cm 30.0; Sftri 2.5 dm (25 mm).

COMPUTATIONS 1. Arm muscle girth, cm ϭ Ϫ ␲ Garm ( Sftri) ϭ 30.0 cm Ϫ (␲2.5 dm) ϭ 30.0 Ϫ 7.854 ϭ 22.1 cm

Fat Muscle Bone

A Upper-arm composition and areaB Relaxed triceps arm girth, cmC Triceps skinfold, mm 97818_ch19.qxd 8/4/09 4:16 PM Page 398

398 Section 3 Aerobic Systems of Energy Delivery and Utilization

Inhibitory Spinal cord interneuron

Sensory nerve from tendon organ

Alpha motor neuron

Capsule

Sensory fiber

Collagen fibrils

Golgi tendon organ

Figure 19.15 • Golgi tendon organ, named for the Italian anatomist and Nobel laureate Camillo Golgi who first described these proprioceptors in the late 1800s. Excessive tension or stretch on a muscle activates the Golgi receptors to initiate a reflex inhibition of the muscles they supply. The Golgi tendon organ functions as a protective sensory mechanism to detect and subsequently inhibits undue strain within the muscle–tendon structure.

stimulus and then remain electrically silent or they discharge 5. The spinal cord and other subconscious areas of the a second volley of impulses when the stimulus ceases. They CNS control many muscle functions. The reflex arc detect changes in movement or pressure rather than the mag- provides the basic mechanism to process “auto- nitude of movement or the quantity of pressure applied. matic” muscle actions. 6. The motor unit makes up the functional unit of movement. The number of muscle fibers in a motor Summary unit depends on a muscle’s movement function. 1. Neural control mechanisms located in the central Intricate movement patterns require a small fiber- nervous system (CNS) regulate human movement. to-neuron ratio; a single neuron can innervate 1000 2. Skeletal muscles respond to internal and external muscle fibers for gross movements. stimuli where bits of sensory input automatically 7. The anterior motor neuron (cell body, axon, and are coded, routed, organized, and transmitted to the dendrites) transmits electrochemical nerve impulses effector organ—the skeletal muscles. from the spinal cord to the muscle. The dendrites 3. Tracts of neural tissue descend from the brain to receive impulses and conduct them toward the cell influence spinal cord neurons. Neurons in the ex- body; the axon transmits the impulse one way down trapyramidal tract control posture and provide a the axon to the muscle. continual background level of neuromuscular tone; 8. The neuromuscular junction (NMJ) establishes the the pyramidal tract neurons stimulate discrete mus- interface between motor neuron and muscle fiber. cular movements. Acetylcholine (ACh) release at the NMJ provides 4. The cerebellum fine-tunes muscle activity through the chemical stimulus that activates the muscle fiber. its function as the major comparing, evaluating, and 9. Stimulation of a muscle fiber progresses in the integrating center. following six-step sequence: (1) action potential 97818_ch19.qxd 8/4/09 4:16 PM Page 399

CHAPTER 19 Neural Control of Human Movement 399 propagates down the motor neuron’s axon; (2) cal- 13. Muscle force gradation progresses through the cium channels open at the end of the nerve termi- interaction of factors that regulate the number and nal; (3) calcium moves into the nerve terminal; type of motor units recruited and their discharge (4) ACh primes for release; (5) ACh traverses the frequency. Low-intensity exercise recruits slow- synapse and binds to ACh receptors on the postsy- twitch motor units, followed by fast-twitch unit naptic membrane at the sarcolemma; and (6) end- activation when requiring more-powerful forces. plate potential generates and a depolarization wave 14. Alterations in motor unit recruitment and firing pat- spreads throughout the T-tubular network. tern help to explain the rapid strength improvement 10. Excitatory and inhibitory impulses continually bom- during the early stages of resistance training. bard the synaptic junctions between neurons. These 15. Sensitive sensory receptors in muscles, tendons, impulses alter a neuron’s threshold for excitation by and joints relay information about muscle dynamics increasing or decreasing its tendency to fire. and limb movement to specific portions of the CNS 11. During all-out power exercise, a high degree of to provide important sensory feedback during phys- neural facilitation (disinhibition) proves beneficial ical activity. because it maximally activates a muscle’s motor 16. Golgi sensory receptors are sensitive to quick units. movement and deep pressure. Pacinian corpuscles 12. Motor units classify into three types depending on detect changes in movement or pressure. speed of muscle action, force generated, and fatigability: (1) fast twitch, high force, fast fatigue; (2) fast twitch, moderate force, fatigue resistant; and References are available online at http://thepoint.lww.com/mkk7e. (3) slow twitch, low force, fatigue resistant. 97818_ch20.qxd 8/4/09 11:56 PM Page 400

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise

CHAPTER OBJECTIVES

➤ Draw the locations of the body’s major endocrine ➤ List the thyroid gland hormones, their functions, glands and how acute and chronic physical activity affect their release ➤ List the sequence of events to show how hormones affect specific “target cell” functions ➤ List the adrenal medulla and adrenal cortex hormones, their functions, and how acute and ➤ Outline the role of the intracellular messenger chronic physical activity affect their release cyclic 3,5-adenosine monophosphate (cyclic AMP) ➤ List hormones of the - and -cells of the pancreas, their functions, and how acute and chronic ➤ Explain how hormones affect enzyme activity and physical activity affect their release enzyme-mediated membrane transport ➤ Define type 1 and type 2 diabetes and the symp- ➤ Describe the influence of hormonal, humoral, and toms and effects of each disorder neural stimulation on endocrine gland activity ➤ Describe three test options for diagnosing ➤ List the anterior and posterior pituitary gland hor- diabetes mellitus mones, their functions, and how acute and chronic physical activity affect their release

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CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 401

➤ List the fasting blood glucose classification cate- ➤ Describe the effect of resistance training on gories for type 2 diabetes testosterone and growth hormone release ➤ List risk factors for type 2 diabetes and benefits of ➤ Characterize the functions of opioid peptides, regular physical activity to prevent and treat this their response to physical activity, and possible disease role in the “exercise high” ➤ Outline how exercise training affects endocrine ➤ Outline interactions among short-term, moder- function ate, and exhaustive exercise, exercise training, susceptibility to illness, and immune function

The endocrine system integrates and regulates bodily glands of the upper digestive tract. The nervous system con- functions to stabilize the internal environment. Hormones trols almost all exocrine glands. produced by endocrine glands affect all aspects of human function; they activate enzyme systems, alter cell membrane Types of Hormones permeability, trigger muscular contraction and relaxation, stimulate protein and fat synthesis, initiate cellular secretion, Hormones, chemical substances synthesized by specific host and determine how the body responds to physical and psycho- glands, enter the bloodstream for transport throughout the logic stress. The following sections provide a general body. Hormones generally fit into one of two categories: overview of the endocrine system, its functions during rest steroid-derived hormones and amine and polypeptide hor- and physical activity, and responses to acute exercise and mones synthesized from amino acids. In contrast to steroid training. hormones, amine and peptide hormones are soluble in blood plasma. This allows easy uptake at target sites. The term half- life describes the time required to reduce a hormone’s blood ENDOCRINE SYSTEM OVERVIEW concentration by one-half. For example, the half-life of epi- Relatively small compared with other body organs, the nephrine is slightly less than 3 minutes. Most orally con- combined weight of the endocrine organs averages 0.5 kg. sumed anabolic hormones such as testosterone have a FIGURE 20.1 shows the location of the major endocrine half-life of approximately 3.5 hours. A hormone’s half-life organs—the pituitary, thyroid, parathyroid, adrenal, pineal, gives a good indication of how long its effect persists. TABLE and thymus glands. Several other organs contain discrete 20.1 compares the storage, synthesis, release mechanism, areas of endocrine tissue that also produce hormones. These transport medium, receptor location and receptor-ligand include the pancreas, gonads (ovaries and testes), hypothala- binding, and target organ response of the peptide, steroid, mus, and adipose (fat) tissues. The hypothalamus also serves and amine hormones. as a major organ of the nervous system; thus it functions as a TABLE 20.2 lists eight different hormones produced by neuroendocrine organ. Pockets of hormone-producing cells organs other than the major endocrine glands. Of these, also form in the walls of the small intestine, stomach, kidneys, prostaglandins constitute a third chemical class of hormones; and myocytes in the heart’s atria, although these organs exert they represent biologically active lipids in the plasma mem- little influence on hormone production per se. brane of nearly all cells. Erythropoietin, a glycoprotein, stimulates the bone marrow’s production of red blood cells. Most hormones circulate in the blood as messengers that ENDOCRINE SYSTEM ORGANIZATION affect tissues a distance from the specific gland. Other hor- The endocrine system (the term endocrine means “hormone mones (e.g., prostaglandins and the gastrointestinal hormone secreting”) consists of a host organ (gland), minute quantities gastrin) exert local effects in their region of synthesis. of chemical messengers (hormones), and a target or receptor organ. Glands classify as either endocrine or exocrine. Some Hormone–Target Cell Specificity glands serve both functions. Hormones alter cellular reactions of specific “target cells” in Endocrine glands possess no ducts (referred to as duct- four ways: less glands) and secrete substances directly into extracellular spaces around the gland. FIGURE 20.2 shows that these hor- 1. Modify the rate of intracellular protein synthesis by mones then diffuse into blood for transport throughout the stimulating nuclear DNA body to fulfill their intercellular communication functions. 2. Change rate of enzyme activity Exocrine glands, in contrast, contain secretory ducts that 3. Alter plasma membrane transport via a second- carry substances directly to a specific compartment or sur- messenger system face. Examples of exocrine glands include sweat glands and 4. Induce secretory activity 97818_ch20.qxd 8/4/09 11:56 PM Page 402

402 Section 3 Aerobic Systems of Energy Delivery and Utilization

Pineal gland

Hypothalamus

Pituitary gland

Thyroid gland

Parathyroid glands

Thymus gland

Adrenal gland

Pancreas

Ovary (female gonad)

Testis (male gonad)

Figure 20.1 • Location of the hormone-producing endocrine organs.

A target cell’s response to a hormone depends largely membrane. Hormone receptors exist in specific local areas on the presence of specific protein receptors that bind the or more diffusely throughout the body. For example, adrenal hormone in a complementary way. Target cell receptors cortex cells contain receptors for adrenocorticotropic hor- occur either on the plasma membrane (up to 10,000 recep- mone (ACTH). In contrast, all cells contain receptors for tors per cell) or in the cell’s interior switch as occurs for thyroxine, the principal hormone that stimulates cellular fat-soluble steroid hormones that pass through the plasma metabolism. 97818_ch20.qxd 8/4/09 11:56 PM Page 403

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 403 membrane alters the target cell’s permeability to a particular Hypothalamus chemical (e.g., insulin’s effect on cellular glucose uptake) or modifies the target cell’s ability to manufacture intracellular substances, primarily proteins. Such actions ultimately affect cellular function. FIGURE 20.3 shows that for the nonsteroid hormones epinephrine and glucagon, the binding hormone acts as first messenger to react with the enzyme adenylate cyclase in the plasma membrane. This forms the compound cyclic 3؅5؅-adenosine monophosphate (cyclic AMP) from an original ATP molecule. Cyclic AMP then acts as a ubiquitous second messenger to activate a specific Kidney Receptor protein kinase, which then activates a target enzyme to alter cellular function. The sequence of reactions set into motion by cyclic AMP Pituitary depends on three factors: endocrine cells 1. Type of target cell 2. Specific enzymes contained in the target cell 3. Specific hormone that acts as first messenger In thyroid cells, for example, cyclic AMP promotes thy- Hormone molecules roxine synthesis from the binding of thyroid-stimulating hormone. In bone and muscle, cyclic AMP produced via growth-hormone binding activates anabolic reactions to synthesize amino acids into tissue proteins.

Hormone Effects on Enzymes Major hormone actions include altering enzyme activity and enzyme-mediated membrane transport. A hormone in- Target cell with hormone binding creases enzyme activity in one of three ways: to receptor 1. Stimulates enzyme production Figure 20.2 • Hormones secreted from endocrine glands 2. Combines with the enzyme to alter its shape and travel in the bloodstream to exert influence on body tissues. ability to act (a chemical process known as allosteric modulation), which increases or decreases the enzyme’s catalytic effectiveness Hormone–Receptor Binding 3. Activates inactive enzyme forms, thus increasing the total amount of active enzyme HormoneÐreceptor binding is the first step in initiating hormone action. The extent of a target cell’s activation by a In addition to altering enzyme activity, hormones either hormone depends on three factors: facilitate or inhibit uptake of substances by cells. Insulin, for example, facilitates glucose transport into the cell by combin- 1. Hormone concentration in the blood ing with extracellular glucose and a glucose carrier within the 2. Number of target cell receptors for the hormone plasma membrane. In contrast, epinephrine inhibits insulin re- 3. Sensitivity or strength of the union between hormone lease, thus slowing cellular glucose uptake. and receptor Hormone action can exert potent (although often indi- Consider cell hormone receptors as dynamic structures that rect) secondary effects. For instance, insulin release in- continually adjust to physiologic demands. Upregulation creases glucose uptake by muscle fibers (primary effect), describes the state whereby target cells form more receptors in which in turn increases muscle glycogen synthesis (second- response to increasing hormone levels (to increase the hor- ary effect). This effect of insulin on glucose uptake (and mone’s effect). In contrast, prolonged exposure to high hormone glycogen synthesis) maintains fuel homeostasis during exer- concentrations desensitizes target cells to blunt hormonal stimu- cise. In insulin-deficient individuals, depressed glucose me- lation. Such downregulation also involves a loss of receptors to tabolism impairs exercise performance. Inadequate cellular prevent target cells from overresponding to chronically high glucose uptake from chronic insulin deficiency abnormally hormone levels (to decrease the hormone’s effect). increases blood glucose concentrations. In the extreme, glucose spills into the urine. We discuss the conditions of in- Cyclic AMP: The Intracellular Messenger. The bind- sulin insufficiency and/or insulin resistance in more detail ing of a hormone with its specific receptor in the plasma on pp. 421Ð429. 97818_ch20.qxd 8/4/09 11:56 PM Page 404

404 Section 3 Aerobic Systems of Energy Delivery and Utilization

TABLE 20.1 • Storage, Synthesis, Release Mechanism, Transport Medium, Receptor Location and Receptor-Ligand Binding, and Target Organ Response of the Peptide, Steroid, and Amine Hormones

Amine Hormones

Thyroid Peptide Hormones Steroid Hormones Catecholamines Hormones

Examples Insulin, glucagon, Androgens, DHEA, cortisol Epinephrine, Thyroxine (T4) leptin, IGF-1 norepinephrine Synthesis and storage Made in advance; stored Synthesized on demand Made in advance; stored Made in advance; in secretory vesicles from precursors in secretory vesicles precursor stored in secretory vesicles Release from Exocytosisa Simple diffusion Exocytosis Simple diffusion parent cell Transport medium Dissolved in plasma Bound to carrier proteins Dissolved in plasma Bound to carrier proteins Lifespan (half-lifeb) Short Long Short Long Receptor location On cell membrane Cytoplasm of nucleus; On cell membrane Nucleus some have membrane receptors Response to Activation of second Activate genes for Activation of second Activate genes for receptor-ligand messenger system; may transcription and messenger system transcription and bindingc activate genes translation; may have translation nongenomic actions General target Modification of existing Induction of new Modification of Induction of new response proteins and induction protein synthesis existing proteins protein synthesis of new protein synthesis

aProcess in which intracellular vesicles fuse with the cell membrane and release their contents into the extracellular fluid. bAmount of time required to reduce hormone concentration by one-half. cA ligand (the molecule that binds to a receptor) binds to a membrane protein, which triggers endocytosis (process of how a cell brings molecules into the cytoplasm in vesicles formed from the cell membrane).

Factors That Determine Hormone Levels 1. Quantity synthesized in the host gland 2. Rate of either catabolism or secretion into the blood Hormone secretion rarely occurs at a constant rate. As with 3. Quantity of transport proteins present (for some nervous system activity, hormone secretion usually adjusts hormones) rapidly to meet the demands of changing bodily conditions. 4. Plasma volume changes For this reason, all protein hormones secrete in a pulsatile manner (see next section). Four factors determine plasma Hormone secretion rate depends on the magnitude of concentration of a particular hormone: chemical stimulatory or inhibitory input from more than one

Extracellular Intracellular space space Inactive Hormone target Adenylate ATP enzyme cyclase Active target enzyme

Active Cyclic Protein +=protein AMP kinase kinase

Specific receptor Bilayer plasma Cellular membrane response

Figure 20.3 • Action of nonsteroid hormones. Circulating hormone (first messenger) binds to a specific receptor in the cell’s plasma membrane to trigger production of cyclic AMP from ATP catalyzed by adenylate cyclase. Cyclic AMP then acts as second messenger to activate a protein kinase within the cell. This in turn activates a target enzyme to elicit the cellular response. 97818_ch20.qxd 8/4/09 11:56 PM Page 405

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 405

TABLE 20.2 • Hormones Produced by Organs Other than the Major Endocrine Organs

Source and Hormone Composition Stimulus for Secretion Target and Outcome

Prostaglandins 20-carbon fatty acid Source: plasma membrane Target: multiple sites synthesized from of different body cells Outcome: controls local hormone response; arachidonic acid Stimulus: local irritation, stimulates arterioles to increase blood pressure; different hormones increases uterine contractions, HCl and pepsin secretion in stomach, platelet aggregation, blood clotting, constriction of bronchioles, inflammation, pain, and fever Gastrin Peptide Source: stomach Target: stomach Stimulus: food Outcome: release of HCl Enterogastrin Peptide Source: duodenum Target: stomach Stimulus: food (especially Outcome: inhibits HCl secretion and gastro- lipids) intestinal motility Secretin Peptide Source: duodenum Target: pancreas Stimulus: food Outcome: release of bicarbonate-rich juice Target: liver Outcome: release of bile Target: stomach Outcome: inhibits secretion Cholecystokinin Peptide Source: duodenum Target: pancreas Stimulus: food Outcome: release of bicarbonate-rich juice Target: gallbladder Outcome: expulsion of bile Target: sphincter of Oddi Outcome: relaxes sphincter and allows bile to enter duodenum Erythropoietin Glycoprotein Source: kidneysa Target: bone marrow Stimulus: hypoxia Outcome: production of red blood cells

Active vitamin D3 Steroid Source: kidneys activate Target: intestine vitamin D from Outcome: active transport of dietary Ca across epidermal skin cells intestinal membranes Stimulus: parathyroid hormone Atrial natriuretic Peptide Source: atrium of heart Target: kidneys hormone Stimulus: atrial stretching Outcome: inhibits Na reabsorption and renin release Target: adrenal cortex Outcome: inhibits secretion of aldosterone

aThe kidneys release an enzyme that modifies a circulating blood protein to produce erythropoietin.

source. Insulin secretion from the pancreas, for example, re- inactive). Hormone inactivation takes place at or near recep- sponds directly to plasma changes in glucose and amino tors or in the liver or kidneys. Because blood flow to acids, norepinephrine (from sympathetic neurons) and circu- splanchnic and renal areas decreases during physical activity lating epinephrine, and acetylcholine released from parasym- (blood distributes to active muscle), hormone inactivation pathetic neurons. Each of these chemical messengers supplies rate decreases and plasma hormone concentration rises. inhibitory or excitatory input that determines whether insulin Changes in plasma volume also alter hormone concen- secretion increases or decreases. Over an extended time (dif- trations, independent of the host organ’s secretion rate. For ferent for each hormone), hormone synthesis tends to equal example, decreased plasma volume during prolonged exer- hormone release. For a relatively short time, however, hor- cise concurrently increases plasma hormone concentration, mone release can exceed its synthesis. The term secreted even without an absolute change in hormone amount. amount describes the plasma concentration of a hormone. In FIGURE 20.4 shows that three factors—hormonal, hu- reality, this represents the sum of hormone synthesis and re- moral, and neural—stimulate endocrine gland activity. lease by the host gland, in addition to its uptake by receptor tissues and removal by liver and kidneys. 1. Hormonal stimulation: Hormones influence secretion Hormone concentration depends on its rate of secretion of other hormones. For example, release-inhibiting into the blood and/or the rate of its metabolism (i.e., it becomes hormones produced by the hypothalamus regulate 97818_ch20.qxd 8/4/09 11:56 PM Page 406

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Anterior pituitary 1 Central Nervous System Capillary blood (spinal cord) containing high 5 Low blood 4 concentration 1 Glucocorticoids of glucose sugar levels ACTH released exert negative inhibit insulin into blood feedback on release ACTH release Pancreas 1 Preganglionic sympathetic nerve fiber stimulates adrenal medullary Adrenal cells cortex 2 Insulin secreted by pancreas Medulla of adrenal gland

2 Adrenal cortex secretes glucocorticoids 2 Adrenal medullary cells secrete catecholamines into blood

3 Target cells 4 absorb more Capillary blood 3 glucose from in which glucose Glucocorticoids blood influence several levels have target organs dropped A Hormonal B Humoral C Neural

Figure 20.4 • Endocrine gland stimulation. A. Hormonal. Adrenocorticotropic hormone (ACTH) stimulates release of glucocorticoid hormones by the adrenal cortex. B. Humoral. High blood glucose concentrations trigger insulin release, causing rapid cellular glucose uptake. The subsequent decrease in blood glucose removes the stimulus for insulin release. C. Neural. Sympathetic nervous system fibers trigger catecholamine release to blood. (From Marieb E, Hoehn K. Human anatomy and physiology. 7th edition, Redwood City, CA: Benjamin/Cummings, 2007)

the secretion of most anterior pituitary hormones. 3. Neural stimulation: Neural activity affects hormone Anterior pituitary hormones, in turn, stimulate other release. For example, sympathetic neural activation endocrine organs to release their hormones into the of the adrenal medulla during stress releases epi- bloodstream. The increased blood levels of a hormone nephrine and norepinephrine. The nervous system produced by the final target gland provide feedback can override normal endocrine control to maintain to inhibit release of anterior pituitary hormones and homeostasis. Insulin action normally maintains blood ultimately their own release. sugar levels between 80 and 120 mg per 100 mL 2. Humoral stimulation: Changing levels of ions and (1 dL) of blood. During exercise, activation of the nutrients in blood, bile, and other body fluids stimu- hypothalamus and sympathetic nervous system late hormone release. The term humoral stimuli de- blunts insulin release to attenuate a further decline in scribes these chemicals to distinguish them from blood sugar and ensure sufficient carbohydrate to hormonal stimuli, which also are fluid-borne chemi- fuel neural tissue and active muscle. cals. For example, an increase in blood sugar concentration (the humoral agent) prompts the pancreas Patterns of Hormone Release to release insulin. Insulin promotes glucose entry into cells, causing blood sugar levels to decline, end- Most hormones respond to peripheral stimuli on an ing the humoral stimulus for insulin release. as-needed basis. Others release at regular intervals during 97818_ch20.qxd 8/4/09 11:56 PM Page 407

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 407 a 24-hour cycle referred to as a diurnal pattern, or cycle, Growth Hormone of secretion. Some secretory cycles span several weeks while others follow daily cycles. Cycling patterns are not Growth hormoneÐreleasing factor from the hypothala- confined to one category of hormones. Pulsatile hormone mus influences resting growth hormone (GH) secretion by release patterns reveal information not available from a directly stimulating the anterior pituitary gland. GH (also called single blood sample that fails to show potentially significant somatotropin) represents a family of related polypeptides variation in hormone levels during a daily cycle. Patterns (derived from one gene) that exert widespread physiologic of release and/or amplitude and frequency of discharge activity because they promote cell division and cellular prolif- provide more meaningful information regarding hormone eration throughout the body. In adults, GH facilitates protein dynamics than simply examining mean concentration at any synthesis in three ways: single time. 1. Increasing amino acid transport through the plasma membrane 2. Stimulating RNA formation INTEGRATIVE QUESTION 3. Activating cellular ribosomes that increase protein Explain the meaning of the following statement: synthesis Hormones act as silent messengers to integrate GH also slows carbohydrate breakdown and initiates the body as a unit. subsequent mobilization and use of fat as an energy source.

Growth Hormone, Physical Activity, and Tissue Synthesis. Increased physical activity of relatively short dura- RESTING AND EXERCISE-INDUCED tion stimulates a sharp rise in GH pulse amplitude and the ENDOCRINE SECRETIONS amount of hormone secreted per pulse.12,77,169 Perhaps more importantly, physical activity stimulates release of GH iso- TABLE 20.3 lists the different endocrine host organs and non- forms with extended half-lives, thereby extending GH’s action glandular endocrine tissues, specific hormones secreted, on target tissues.122 Augmented GH release benefits muscle, hormone targets, and main effects. The following sections bone, and connective tissue growth and remodeling. It also review these hormones, with special emphasis on their optimizes the fuel mixture during physical activity, principally immediate response to exercise and adaptations to physical decreasing tissue glucose uptake, increasing free fatty acid training. mobilization, and enhancing liver gluconeogenesis. The net metabolic effect of increased exercise-induced GH production preserves plasma glucose concentration for central nervous system and muscle functions. Many of the growth-promoting Anterior Pituitary Hormones effects of GH result from actions of intermediary chemical FIGURE 20.5 illustrates the pituitary gland (also called the messengers on different target tissues, rather than a direct hypophysis), its secretions, and various target glands and effect of GH itself. These peptide messengers, produced in the their hormone secretions. Located beneath the base of the liver, are termed somatomedins, or insulin-like growth fac- brain, the pituitary secretes at least six specialized polypep- tors (IGF-1 and IGF-II; see next section) because of their tide hormones. Because of its widespread influence, the ante- structural similarity to insulin. These factors exert potent rior pituitary gland was often called the master gland. peripheral effects on motor units and other tissues. Researchers now know that the hypothalamus controls ante- How physical activity stimulates GH release to augment rior pituitary activity; thus, the hypothalamus should truly protein synthesis (and subsequent muscle hypertrophy), carti- claim that distinction. Each of the primary pituitary hormones lage formation, skeletal growth, and cell proliferation remains has its own hypothalamic releasing hormone called a releas- unclear, although the total integrated growth hormone con- ing factor. Neural input to the hypothalamus from anxiety, centration increases with physical activity duration in men stress, and physical activity controls output of these releasing and women.170 Concurrent measurements of circulating lac- factors. In addition to the hormones displayed in Figure 20.5, tate, alanine, and pyruvate; blood glucose; and body tempera- the pituitary secretes proopiomelanocortin (POMC), a large ture reveal no association with GH secretory patterns during precursor molecule of other active molecules. POMC pro- exercise.78 One hypothesis suggests that exercise directly vides the source of a number of neurotransmitters and hor- stimulates GH release (or release of somatomedins from the mones including ACTH, melanocortin peptides, and some of liver or kidneys), which in turn stimulates anabolic processes. the naturally produced opiates such as -endorphin (see Exercise also may indirectly affect GH by stimulating cholin- p. 439). These hormones exert a remarkable range of influ- ergic pathways to trigger GH release. Moreover, it is known ence, including effects on pigmentation, adrenocortical func- that physical activity stimulates endogenous opiate production, food intake and fat storage, and nervous and immune tion that facilitates GH release by inhibiting the liver’s pro- system functions. duction of somatostatin, a hormone that blunts GH release.166 97818_ch20.qxd 8/4/09 11:56 PM Page 408

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TABLE 20.3 • Endocrine Organs and Their Secretions, Targets, and Main Effects

Gland Chemical Location or Cells Type Hormone Target Main Effect

Adipose tissue Cells Peptide Leptin; adiponectin Hypothalamus, Food intake, metabolism, (resistin) other tissues reproduction Adrenal cortex Gland Steroid Mineralocorticoids Kidney Stimulates Na reabsorption (aldosterone) and K secretion Glucocorticoids Many tissues Promotes protein and fat (cortisol; catabolism; raises blood corticosterone) glucose levels; adapts body to stress Androgens Many tissues Promotes sex drive (androstenedione; dehydroepiandrosterone [DHEA]; estrone) Adrenal Gland Amine Epinephrine, Many tissues Facilitates sympathetic activity; medulla norepinephrine increases cardiac output; regulates blood vessels; increases glycogen catabolism and fatty acid release Gastrointestinal Cells Peptide Gastrin; GI tract and Assist digestion and absorption tract (stomach cholecystokinin pancreas of nutrients; regulates and small (CCK); secretin; gastrointestinal motility intestine) glucose-dependent insulinotropic peptide (GIP) Heart Cells Peptide Atrial natriuretic Kidney tubules Inhibits sodium reabsorption peptide (ANP) Hypothalamus Clusters of Peptide Trophic hormones Anterior Release or inhibit anterior neurons (releasing and pituitary pituitary hormones release-inhibiting hormones: corticotropin- releasing hormone [CRH]; thyrotropin- releasing hormone [TRH]; growth hormone-releasing hormone [GHRH]; gonadrotropin- releasing hormone [GnRH]) Kidney Cells Peptide Erythropoietin (EPO) Bone marrow Red blood cell production Steroid 1,25 Dihydroxy- Intestine Increases calcium absorption vitamin D3 (calciferol) Liver Cells Peptide Angiotensinogen Adrenal cortex, Aldosterone secretion; increases blood vessels, blood pressure brain Insulin-like growth Many tissues Growth factors (IGF-1) Muscle Cells Peptide Insulin-like growth Many tissues Growth factors (IGF-1, IGF-II); myogenic regulatory factors (MRFs) Pancreas Gland Peptide Insulin Many tissues Lowers blood glucose levels; promotes protein, lipid, and glycogen synthesis Glucagon Many tissues Raises blood glucose levels; promotes glycogenolysis and gluconeogenesis

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CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 409

TABLE 20.3 • Endocrine Organs and Their Secretions, Targets, and Main Effects continued Gland Chemical Location or Cells Type Hormone Target Main Effect

Somatostatin (SS) Many tissues Inhibits secretion of pancreatic hormones; regulates digestion and absorption of nutrients by GI system Parathyroid Gland Peptide Parathyroid Bone, kidney Promotes Ca2 release from hormone (PTH) bone, Ca2 absorption by intestine, and Ca2 reabsorption by kidney; raises blood Ca2 levels; stimulates vitamin D3 synthesis Pineal gland Gland Amine Melatonin Unknown Controls circadian rhythms Pituitary- Gland Peptides Growth hormone Many tissues Growth; stimulates bone and anterior (GH) soft tissue growth; regulates protein, lipid, and CHO metabolism Adrenocorticotropic Adrenal cortex Stimulates glucocorticoid hormone (ACTH) secretion Thyroid-stimulating Thyroid gland Stimulates secretion of thyroid hormone (TSH) hormones Prolactin Breast Milk secretion Follicle-stimulating Gonads Females: stimulates growth and hormone (FSH) development of ovarian follicles and estrogen secretion; Males: sperm production by testis Luteinizing hormone Gonads Females: stimulates ovulation, (LH) secretion of estrogen and progesterone; Males: testosterone secretion by testis Pituitary- Extension of Peptide Oxytocin (OT) Breast and Females: stimulates uterine posterior hypothalamic uterus contractions and milk neurons ejection by mammary glands; Males: unknown function Antidiuretic hormone Kidney Decreases urine output by (ADH or kidneys; promotes blood vasopressin) vessel (arteriole) constriction Placenta Gland Steroid Estrogens and Many tissues Fetal and maternal development (pregnant progesterone female) Peptide Chorionic Metabolism somatomam- motropin (CS) Chorionic Hormone secretion gonadotropin (CG) Skin Cells Steroid Vitamin D3 Intermediate Precursor of 1,25 hormone form dihydroxy-vitamin D3 Ovaries (female) Glands Steroid Estrogens (estradiol) Many tissues Egg production; secondary sex characteristics Progestins Uterus Promotes endometrial growth to (progesterone) prepare uterus for pregnancy Peptide Ovarian inhibin Anterior pituitary Inhibits FSH secretion Testes (male) Glands Steroid Androgen Many tissues Sperm production; secondary sex characteristics Peptide Inhibin Anterior pituitary Inhibits FSH secretion Thymus Gland Peptide Thymosin, thymopoi- Lymphocytes Stimulates proliferation and etin function of T lymphocytes Thyroid Gland Iodinated Triiodothyronine (T3); Many tissues Increases metabolic rate; amines thyroxine (T4) normal physical development Peptide Calcitonin (CT) Bone Promotes calcium deposition in bone; lowers blood calcium levels 97818_ch20.qxd 8/4/09 11:56 PM Page 410

410 Section 3 Aerobic Systems of Energy Delivery and Utilization

Hypothalamus Lactogen Breast (prolactin)

Gonadotropic Ovaries Estrogen, Progesterone hormones (FSH, LH) Testes Testosterone Hypophyseal stalk ACTH Adrenal Cortisol (corticotropin) cortex Anterior Aldosterone pituitary Thyroxine (T4) Posterior Thyrotropin Thyroid pituitary Triiodothyronine (T3)

Pars Growth hormone intermedia (somatotropin) Many organs

Endorphins Diverse organs and tissues

Figure 20.5 • The pituitary gland, its secretions, and targets.

FIGURE 20.6 outlines the overall metabolic actions of GH; Adrenocorticotropic Hormone it modulates the metabolic mixture during physical activity by stimulating fatty acid release from adipose tissue while simul- ACTH, known as corticotropin, functions as part of the taneously inhibiting cellular glucose uptake. This glucose- hypothalamicÐpituitaryÐadrenal axis that regulates adrenal sparing action maintains blood glucose at relatively high cortex output of hormones in a manner similar to TSH control levels to augment prolonged exercise performance. of thyroid gland secretion. ACTH acts directly to enhance Trained and sedentary individuals show similar in- fatty acid mobilization from adipose tissue, increase gluco- creases in GH concentration with exercise to exhaustion. In neogenesis, and stimulate protein catabolism. Owing to diffi- contrast, the sedentary person maintains higher GH levels for culty in assay methods and rapid disappearance of this several hours into recovery. During a standard bout of sub- hormone from the blood, data remain scarce concerning maximal exercise, sedentary individuals have a greater GH ACTH response during physical activity. ACTH concentrations may increase proportionately with exercise intensity and response. The absolute submaximal exercise level represents 37 greater stress for the less fit person allowing GH release to re- duration if intensity exceeds 25% of aerobic capacity. late more to the relative strenuousness of physical effort. Corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mediate ACTH release. CRH exhibits a defi- Insulin-Like Growth Factors nite diurnal rhythm, with highest levels in early morning just after rising. As the day progresses, CRH levels decline, IGFs (somatomedins) mediate many of GH’s effects. In essentially blocking ACTH release. Factors that alter the nor- response to GH stimulation, liver cells synthesize IGF-I and mal ACTH rhythm by triggering CRH release include fever, IGF-II, a process that requires between 8 and 30 hours. IGFs hypoglycemia, and other stressors. CRH is both an ACTH travel in the blood attached to one of five types of binding regulator and a central nervous system neurotransmitter, and proteins for release as free hormones to interact with specific often is termed the stress response integrator. High-intensity receptors. The factors that influence IGF transport include physical activity favors AVPrelease while prolonged physical binding proteins within muscle, nutritional status, and plasma activity favors CRH release, both inhibiting ACTH.68 insulin levels. Prolactin Thyrotropin Prolactin (PRL) initiates and supports milk secretion Thyrotropin, also known as thyroid-stimulating hor- from the mammary glands. PRL levels increase at high exercise mone (TSH), controls hormone secretion by the thyroid intensities and return toward baseline within 45 minutes during gland. TSH maintains growth and development of the thyroid recovery. Owing to its important role in female sexual function, gland and increases thyroid cell metabolism. Considering the repeated exercise-induced PRL release may inhibit ovarian important role of thyroid hormones in regulating overall body function and contribute to menstrual cycle alterations when metabolism, one would expect TSH output from the pituitary females train intensely. Greater increases in PRL occur in to increase during physical activity, but this response does not women who run without wearing an undergarment support;130 occur consistently. either fasting or consuming a high-fat diet enhances release of 97818_ch20.qxd 8/4/09 11:56 PM Page 411

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 411 Hypothalamus

Inhibits GHRH Secretes GHRH, release GHIH, or somatostatin

Feedback Stimulates control GHIH release

Inhibits GH synthesis and release Anterior pituitary

Growth hormone

Indirect actions Liver and Direct actions (promote other organs (anti-insulin) anabolism)

Somatomedins

Skeletal Nonskeletal Adipose effects effects tissue Hinders glucose uptake to maintain blood Increases Increases synthesis Triacylglycerol sugar level formation of protein and new release of cartilage cell growth

Promotes skeletal growth

Figure 20.6 • Overview of growth hormone (GH) actions. GH stimulates breakdown and release of triacylglycerols from adipose tissue and hinders cellular glucose uptake (antiinsulin effect) to maintain a relatively high blood glucose level. Somatomedins mediate the indirect anabolic effects of GH. Elevated GH levels and somatomedins provide feedback to promote GH-inhibiting hormone (GHIH) release and depress hypothalamic release of GH-releasing hormone (GHRH); this further inhibits GH release by the anterior pituitary gland.

this hormone.73 PRL concentration also increases in men complements FSH action to cause estrogen secretion and following maximal exercise.27 rupture of the follicle, which allows the ovum to pass through the fallopian tube for fertilization. In the male, FSH stimulates germinal epithelium growth in the testes to promote Gonadotropic Hormones sperm development. LH also stimulates the testes to secrete Gonadotropic hormones stimulate the male and female testosterone. sex organs to grow and secrete their hormones at a faster rate. Inconsistent reports describe short-term exercise-associated The two gonadotropic hormones are follicle-stimulating alterations in FSH and LH. LH release is normally pulsatile, hormone (FSH) and luteinizing hormone (LH). FSH initi- making it difficult to separate any specific exercise-related ates follicle growth in the ovaries and stimulates these organs change from the normal pulsatile pattern. Generally, LH concen- to secrete estrogen, one type of female sex hormone. LH tration rises before exercise begins and peaks during recovery. 97818_ch20.qxd 8/4/09 11:56 PM Page 412

412 Section 3 Aerobic Systems of Energy Delivery and Utilization

Posterior Pituitary Hormones gain in most individuals. For nervous system function, T3 release facilitates neural reflex activity, whereas low T4 levels The posterior pituitary gland forms as an outgrowth of the cause sluggishness, often inducing people to sleep for up to hypothalamus and resembles true neural tissue (see Fig. 20.5). 15 hours a day. Thyroid hormones provide important regula- This tissue, often called the neurohypophysis, stores anti- tion for tissue growth and development, skeletal and nervous diuretic hormone (ADH, or vasopressin) and oxytocin. The system formation, and maturation and reproduction. They posterior pituitary does not synthesize its hormones. Instead, also play a role in maintaining blood pressure by provoking the hypothalamus produces these hormones and secretes them an increase in adrenergic receptors in blood vessels. to the neurohypophysis for release as needed via neural stim- Whole-body metabolism influences synthesis of thyroid ulation. Damage or surgical removal of the posterior pituitary hormones. Depressing the metabolic rate to some critical does not dramatically affect ADH or oxytocin production. value directly stimulates hypothalamic release of TSH. This ADH influences water excretion by the kidneys. Its ac- increases thyroid output and increases resting metabolism. tion limits production of large volumes of urine by stimulating Conversely, a chronic elevation in metabolism reduces TSH water reabsorption in the kidney tubules. Oxytocin initiates production, causing metabolism to slow. FIGURE 20.7 illus- muscle contraction in the uterus and stimulates ejection of trates this exquisitely regulated feedback system. milk during lactation. During physical activity, blood levels of free T4 (thyrox- Physical activity provides a potent stimulus for ADH ine not bound to plasma proteins) increase by approximately secretion. Increased ADH release, probably stimulated by 35%. This increase could occur from an exercise-induced ele- sweating, helps to conserve body fluids during hot-weather vation in core temperature, which alters the protein binding of physical activity and accompanying dehydration. This water- several hormones, including T4. The importance of these tran- conserving effect of ADH contributes to efficient modulation 104 sient exercise-induced alterations in thyroid hormone dynam- of the cardiovascular response to physical activity. ADH ics requires further study. release decreases with fluid overload, thus increasing urine volume and producing more dilute urine (i.e., lighter color Thyroid Hormones Affect Quality of Life urine). The effect of short-term physical activity on oxytocin release remains unknown. Thyroid hormones are not essential for life but they do affect life’s quality. In children, full expression of growth Thyroid Hormones hormone requires thyroid activity. Thyroid hormones provide The 15- to 20-g reddish brown thyroid gland, located nearer the first part of the trachea just below the larynx, comes under the in- Hypothalamus fluence of TSH produced by the anterior pituitary gland. In addition to secreting the calcium-regulating hormone calcitonin, the thyroid gland secretes two protein-iodineÐbound hormones, thyroxine (T4) and triiodothyronine (T3, the active form of thyroid hormone). These two hormones are often referred to as major TSH metabolic hormones. More T4 is secreted than T3; although less Inhibition of hypothalamic factor abundant, T3 acts several times faster than T4. The majority of T3 stimulation of anterior pituitary comes from the deiodination of T4 in peripheral tissues, princi- Anterior pituitary pally liver and kidney. Most receptor cells for T4 metabolize it to T3. T3 and T4 are not readily soluble in water, which means they bind to carrier proteins that circulate in blood. Thyroxine- Increased rate of cellular metabolism Secretion of binding globulin (glycoprotein synthesized in the liver) serves as thyrotropin the main transporter of thyroid hormones. This carrier protein (along with two others—transthyretin and albumin) permits a more consistent availability of thyroid hormones from which the Secretion of thyroxine active, free hormones release for target cell uptake. Through its stimulating effect on enzyme activity, T4 secretion raises metabolism of all cells except in the brain, spleen, testes, uterus, and thyroid gland itself. For example, Larynx (posterior abnormally high T4 secretion raises basal metabolic rate view) (BMR) up to fourfold. This potent thermogenic effect pro- Parathyroid glands duces large BMR deviations that often indicate thyroid gland abnormality (see Chapter 9). A person may lose weight rap- Thyroid gland idly with abnormally high thyroid activity. In contrast, de- (posterior view) Esophagus pressed thyroid production blunts BMR, which usually leads Trachea to gains in body weight and body fat. However, fewer than 3% of obese persons show abnormal thyroid functions, so de- Figure 20.7 • Feedback system that controls thyroid pressed thyroid activity cannot explain excessive body fat hormone release. 97818_ch20.qxd 8/4/09 11:56 PM Page 413

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 413 essential stimulation for normal growth and development, 3. Depressed reflex activity, slow speech and thought especially of nervous tissue. The actions of thyroid hormones processes, and feeling of fatigue (in infancy causes become most noticeable in people who suffer from either hy- cretinism, marked by decreased mental capacity) persecretion or hyposecretion. 4. Slow heart rate (bradycardia) Hypersecretion of thyroid hormones (hyperthyroidism) produces the following four effects: 1. Increased oxygen consumption and metabolic heat Parathyroid Hormones production during rest (heat intolerance is a common Four parathyroid glands, measuring 6-mm long, 4-mm wide, complaint) and 2-mm deep, embed in the posterior aspect of the thyroid 2. Increased protein catabolism and subsequent muscle gland (FIG. 20.8). As many as eight glands have been reported in weakness and weight loss some people, and glands have been found in other regions of 3. Heightened reflex activity and psychological distur- the neck or in the thorax. Parathyroid hormone (PTH, or bances that range from irritability and insomnia to parathormone) controls blood calcium balance. A decrease in psychosis blood calcium levels triggers PTH release; increasing calcium 4. Rapid heart rate (tachycardia) concentrations inhibit its release. PTH’s major effect increases Hyposecretion of thyroid hormones (hypothyroidism) ionic calcium levels by stimulating three target organs—bone, produces the following four effects: kidneys, and small intestine. PTH release produces the following three effects: 1. Reduced metabolic rate and cold intolerance from reduced internal heat production 1. Activation of bone-reabsorbing cells (osteoclasts) to 2. Decreased protein synthesis produces brittle nails, digest some of the bone matrix to release ionic cal- thinning hair, and dry, thin skin cium and phosphate to the blood

Ca2+ Ca2+

Low blood calcium concentration

Thyroid gland PTH release from (posterior view) parathyroid gland Parathyroid glands

Activates osteoclasts; Increased calcium calcium and phosphorus uptake by released to blood intestinal mucosa

Vitamin D activation

Rise in blood calcium concentration

2+ 2+ Ca 2+ 2+ Ca Ca Ca 2+ 2+ Ca Ca2+ Ca

Figure 20.8 • Dynamics of parathyroid hormone (PTH) release and its actions. 97818_ch20.qxd 8/4/09 11:56 PM Page 414

414 Section 3 Aerobic Systems of Energy Delivery and Utilization

Pituitary Adrenal gland

Corticotropin

Adrenal glands

Kidney

Kidneys Cortex Mineralocorticoids Medulla Aldosterone Corticosterone Catecholamines Deoxycortocosterone Epinephrine Glucocorticoids Norepinephrine Cortisol Androgens

Figure 20.9 • Adrenal gland secretions.

2. Enhancement of calcium ion reabsorption and de- Adrenal Medulla Hormones creased retention of phosphate by the kidneys 3. Increased calcium absorption by intestinal mucosa The adrenal medulla makes up part of the sympathetic nervous system. It acts to prolong and augment sympathetic Plasma calcium ion homeostasis modulates nerve im- effects by secreting epinephrine and norepinephrine, hor- pulse conduction, muscle contraction, and blood clotting. mones collectively called catecholamines. FIGURE 20.10 Limited evidence suggests that physical activity increases shows the chemical structure of epinephrine and norepineph- PTH release in young, middle-aged, and older individuals, an rine and the role of each in substrate mobilization. effect that contributes to the positive effects of mechanical Norepinephrine, a hormone in its own right, serves as an epi- forces from physical activity on bone mass accretion.6,15,88 nephrine precursor. It also acts as a neurotransmitter when released by sympathetic nerve endings. Epinephrine represents Adrenal Hormones 80% of adrenal medulla secretions, whereas norepinephrine provides the principal neurotransmitter released from the The adrenal glands appear as flattened, caplike tissues situ- sympathetic nervous system. An outflow of neural impulses ated just above each kidney (FIG. 20.9). The glands have two from the hypothalamus stimulates the adrenal medulla to in- distinct parts: medulla (inner portion) and cortex (outer crease catecholamine release. These hormones affect the portion). Each part secretes different types of hormones; con- heart, blood vessels, and glands in the same, albeit slower- sequently, the cortex and medulla are generally considered acting way as direct sympathetic nervous system stimula- two distinct glands. tion. Epinephrine’s primary function in energy metabolism 97818_ch20.qxd 8/4/09 11:56 PM Page 415

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 415

O O O O H H H H

) 2.5

CC CC –1 mL

. 2.0 H CCH H CCH

1.5 CC C C

H H H H 1.0 H C H C

H C H C O O 0.5 H H NN H H (ng Blood concentrations 0 H H Rest 50% 75% 100% H C Exercise intensity (% VO2max) H

Norepinephrine Epinephrine Norepinephrine Epinephrine Figure 20.11 • Catecholamine response to exercise of increasing intensity in 10 male subjects. (From Applied Physiology Laboratory, University of Michigan, Ann Arbor.)

Liver adjustments in active tissues. Physical activity also increases Adipose tissue Muscle epinephrine output from the adrenal medulla, with the magnitude of increase related directly to effort intensity and dura- Glycogen Triacylglycerols Blocks tion.24,85,105 Athletes involved in sprintÐpower training show glucose entry greater sympathoadrenergic activation during maximal exer- 148 Glycerol + cise than counterparts trained in aerobic exercise. This Glucose Fatty acids difference relates to the higher anaerobic contribution to maximal exercise energy supply by sprintÐpower athletes. Age Figure 20.10 • Chemical structure of epinephrine and does not affect catecholamine response to physical activity norepinephrine and their role in mobilizing glucose from the among individuals equal in aerobic fitness.79,98 The effects of liver and free fatty acids from adipose tissue (and blunting glucose uptake by skeletal muscle). Norepinephrine serves as increased adrenal medulla activity on blood flow distribution, a hormone and as a precursor of epinephrine. It also cardiac contractility, and substrate mobilization all benefit the functions as a neurotransmitter when released by physical activity response. sympathetic nerve endings. Adrenocortical Hormones stimulates glycogenolysis (in the liver and active muscles) The adrenal cortex, stimulated by corticotropin from the and lipolysis (in adipose tissue and active muscles); norepi- anterior pituitary, secretes adrenocortical hormones. These nephrine provides powerful lipolytic stimulation in adipose corticosteroid hormones fit functionally into one of three tissue.39,150 Sympathetic nerve endings (including those to groups: (1) mineralocorticoids, (2) glucocorticoids, and the adrenal gland) secrete both epinephrine and norepineph- (3) androgens—each produced in a different zone (layer) of rine, so it is more appropriate to discuss the “sympathoad- the adrenal cortex. renal” response to exercise and training rather than the adrenal gland response. The sympathoadrenal response to Mineralocorticoids. As the name suggests, mineralo- physical activity most closely relates to relative rather than corticoids regulate the mineral salts sodium and potassium in absolute activity intensity. the extracellular fluid. Aldosterone, the most physiologically FIGURE 20.11 illustrates the catecholamine response at important of the three mineralocorticoids, represents almost various exercise intensities (expressed as %VO2max) in 10 95% of all mineralocorticoids produced. male subjects. Norepinephrine increases markedly at intensi- FIGURE 20.12 shows four major controlling factors for al- ties that exceed 50% VO2max, whereas epinephrine levels re- dosterone release from the adrenal cortex. Aldosterone secre- main unchanged until exercise intensity exceeds the 60% tion controls total sodium concentration and extracellular level. At maximum effort, an approximate two- to sixfold in- fluid volume. It stimulates sodium ion reabsorption (along crease in norepinephrine release takes place. More than likely, with fluid) in the distal tubules of the kidneys by increasing increased secretion occurs from sympathetic postganglionic synthesis of sodium transporter proteins by the epithelial cells nerve endings and relates to cardiovascular and metabolic of the tubules and collecting duct. Consequently, little sodium 97818_ch20.qxd 8/4/09 11:56 PM Page 416

416 Section 3 Aerobic Systems of Energy Delivery and Utilization

Factor 1 Factor 2 Factor 3 Factor 4 Increase in blood Decrease in blood Decrease in Na+ + pressure or blood volume, decrease Stress and increase in K volume in Na+, or increase in blood in K+ in blood

CRH

Heart Kidney Anterior pituitary Bloodstream Atrial natiuretic Renin converts Direct factor produces angiotensinogen ACTH stimulating inhibitory effect to angiotensin II effect

Adrenal cortex

Adrenal gland Capsule Zona glomerulosa

Zona Adrenal cortex fasciculata

Zona reticularis

Medulla

Zona glomerulosa increases aldosterone secretion

Increase in Na+ and Increase in blood H2O absorption; increase volume and blood in K+ excretion pressure

Figure 20.12 • Four major factors control aldosterone release from the adrenal cortex. CRH, corticotropin-releasing hormone; ACTH, adrenocorticotropic hormone.

(and fluid) voids in the urine. Increases in cardiac output and angiotensin II and angiotensin III. These hormones stimulate arterial blood pressure also accompany increases in plasma arterial constriction and adrenocortical secretion of aldosterone, volume with aldosterone secretion. In contrast, sodium and which causes the kidneys to retain sodium and excrete potas- water literally flow into the urine when aldosterone secretion sium. Renal absorption of sodium also conserves water, causing ceases. Aldosterone also helps to stabilize serum potassium plasma volume to expand and blood pressure to increase. and pH because the kidneys exchange either a K+ or H+ for Chronic reduction in renal blood flow at rest, perhaps each Na+ reabsorbed. Proper mineral balance maintains nerve from abnormal sympathetic stimulation, activates the reninÐ transmission and muscle function. As with all steroid hor- angiotensin system. Hypertension occurs from the prolonged mones, cellular response to increased aldosterone production overresponse of this mechanism with resulting excess aldos- occurs relatively slowly. It requires physical activity in excess terone output. High blood pressure associated with increased of 45 minutes for aldosterone’s effect to emerge; hence, its aldosterone production often occurs in teenage obesity.133 major effects occur during recovery. Teenage hypertension relates to three factors:

ReninÐAngiotensin Mechanism. Increased sympathetic 1. Decreased salt sensitivity (hence increased water nervous system activity during exercise constricts blood vessels retention) that serve the kidneys. Reduced renal blood flow stimulates the 2. Increased sodium intake kidneys to release the enzyme renin into the blood. Increased 3. Decreased sensitivity to the effects of insulin renin concentration stimulates production of two kidney hormones, (hyperinsulinemia) 97818_ch20.qxd 8/4/09 11:56 PM Page 417

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 417 These interrelationships suggest a direct link between running or an intense bout of resistance training.128 Even dur- obesity as a disease and subsequent development of hyperten- ing moderate physical activity, plasma cortisol concentration 32,55 sion. Similar relationships occur in adults. rises with prolonged duration. Data for cortisol turnover indicate that highly trained runners maintain a state of hypercorti- Glucocorticoids. The stress of physical activity stimu- solism that heightens before competition or intense lates hypothalamic secretion of corticotropin-releasing fac- training.43,73 Cortisol levels also remain elevated for up to 2 tor, causing the anterior pituitary to release ACTH. In turn, hours following physical activity. This suggests that cortisol ACTH promotes glucocorticoid release by the adrenal cortex. plays a role in tissue recovery and repair. Unlike the direct, Cortisol (hydrocortisone), the major glucocorticoid of the ad- active metabolic effect of epinephrine and glucagon on fuel renal cortex, affects glucose, protein, and free fatty acid me- homeostasis during exercise, cortisol exerts a more facilitat- tabolism in six ways: ing effect on substrate use.

1. Promotes breakdown of protein to amino acids in all Gonadocorticoids. The reproductive organs (gonads) cells except the liver; the circulation delivers these provide the major source of the so-called sex steroids, but the “liberated” amino acids to the liver for synthesis to adrenal cortex produces androgen hormones (gonadocorti- glucose via gluconeogenesis coids) with similar actions. For example, the adrenal cortex 2. Supports action of other hormones, primarily produces dehydroepiandrosterone, which exerts effects glucagon and GH in the gluconeogenic process similar to the dominant male hormone testosterone. 3. Serves as an insulin antagonist by inhibiting cellular Treatment with 50 mg of dehydroepiandrosterone in women glucose uptake and oxidation with adrenal insufficiency over a 4-month trial improved well 4. Promotes triacylglycerol breakdown in adipose tis- being and sexual responsiveness as well as decreased depres- sue to glycerol and fatty acids sion and anxiety compared to placebo treatment.227 The adre- 5. Suppresses immune system function nal cortex also produces small amounts of the “female” 6. Produces negative calcium balance hormones estrogen and progesterone.

FIGURE 20.13 shows factors that affect cortisol secretion and its effects on target tissues. A strong diurnal pattern gov- GONADAL HORMONES erns cortisol secretion. Secretions normally peak in the morn- The testes in the male and ovaries in the female are the ing and subside at night. Cortisol secretion increases with reproductive glands. These endocrine glands produce hor- stress, making it known as the “stress” hormone. Even though mones that promote sex-specific physical characteristics and considered a catabolic hormone, cortisol’s important effect initiate and maintain reproductive function. No distinctly counters hypoglycemia and is thus essential for life. Animals “male” or “female” hormones exist, but rather general whose adrenal glands have been removed die if exposed to se- differences in hormone concentrations between the sexes. vere environmental stress. Cortisol, required for full activity Testosterone is the most important androgen secreted by the of glucagon and the catecholamines, exerts a facilitating ef- interstitial cells of the testes. FIGURE 20.14 shows that testos- fect on these hormones. terone initiates sperm production and stimulates develop- Chronically high-serum cortisol levels initiate excessive ment of male secondary sex characteristics. Testosterone’s protein breakdown, tissue wasting, and negative nitrogen bal- anabolic, tissue-building role contributes to maleÐfemale dif- ance. Cortisol secretion also accelerates fat mobilization for ferences in muscle mass and strength that emerge at the onset energy during starvation and intense, prolonged physical ac- of puberty. As noted in Chapter 2, testosterone conversion to tivity. With rapid and large increases in cortisol output, the estrogen in peripheral tissues, under control of the enzyme liver splits mobilized fat into its simple ketoacid components. aromatase, provides the male with protection in maintaining Excess ketoacid concentrations in the extracellular fluid can bone structure throughout life. lead to the potentially dangerous condition of ketosis (a form The ovaries provide the primary source of estrogens, of acidosis). Individuals who subsist on very low carbohy- particularly estradiol and progesterone. Estrogens regulate drate, low-calorie weight-loss diets (termed ketogenic diets; ovulation, menstruation, and physiologic adjustments during see Chapter 30) can experience ketosis, augmented by ele- pregnancy. Estrogen circulating in the bloodstream and gen- vated cortisol secretion. erated locally in peripheral tissues also exerts effects on blood Cortisol turnover (difference between its production and vessels, bone, lungs, liver, intestine, prostate, and testes removal) provides a way to study cortisol response to physi- through action on - and -receptor proteins. Progesterone cal activity. Cortisol turnover with physical activity exhibits contributes specific regulatory input to the female reproduc- considerable variability with exercise intensity, fitness level, tive cycle, uterine smooth muscle action, and lactation. nutritional status, and even circadian rhythm.30,152 Most re- Controversy exists concerning the role of estrogen and prog- search indicates that cortisol output increases with exercise esterone in substrate metabolism during physical activity.3,107 intensity; this heightened output accelerates lipolysis, ketoge- Estradiol-17 (biologically active estrogen synthesized from nesis, and proteolysis. Extremely high cortisol levels occur cholesterol) increases free fatty acid mobilization from adi- following long-duration physical activity such as marathon pose tissue and inhibits glucose uptake by peripheral tissues. 97818_ch20.qxd 8/4/09 11:56 PM Page 418

418 Section 3 Aerobic Systems of Energy Delivery and Utilization

Stress Circadian rhythm

Hypothalamus

CRH secretion

Negative feedback

Anterior pituitary

ACTH section

Adrenal Cortex

Cortisol secretion

Many tissues Adipose tissue Muscle tissue Liver

Adipose tissue Protein Gluconeogenesis Glucose uptake synthesis breakdown

Amino acid Protein uptake synthesis

Figure 20.13 • Factors that affect cortisol secretion and its actions on target tissues. CRH, corticotropic releasing hormone; ACTH, adrenocorticotropic hormone.

In this way, the increases in estradiol-17 and GH during Testosterone also interacts with neural receptors to increase physical activity exert similar metabolic influences. neurotransmitter release and initiate structural protein changes that alter the size of the neuromuscular junction. These neural effects enhance force-production capabilities of skeletal Testosterone muscle. Plasma testosterone concentration commonly serves as a Testosterone’s effect on the cell nucleus remains contro- physiologic marker of anabolic status. In addition to its direct versial. More than likely, a transport protein (sex-hormoneÐ effects on muscle tissue synthesis, testosterone indirectly af- binding globulin) delivers testosterone to target tissues, after fects a muscle fiber’s protein content by promoting GH re- which testosterone associates with a membrane-bound or cy- lease leading to IGF synthesis and release from the liver. tosolic receptor. It subsequently migrates to the cell nucleus, 97818_ch20.qxd 8/4/09 11:56 PM Page 419

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 419

Androgen Converted to Estrogen (testosterone from testes)

Libido Hair loss at temple Facial hair Vocal cord enlargement (deepening of voice) Body hair Mineralization Pubic hair of the skeleton

Sperm Growth plate production maturation and fusion

Other Estrogen’s targets: Possible •Muscle strength Functions: •Prostate growth •Increased insulin •Skin glands (acne sensitivity and body odor) •Decreased cardiovascular risk

Figure 20.14 • Androgen’s effects in men. Binding with special receptor sites in muscle and various other tissues, androgen (testosterone) contributes to male secondary sex characteristics and sex differences in muscle mass and strength that develop at the onset of puberty. Some androgen converts to estrogen in peripheral tissues and gives males a considerable edge over females in maintaining bone mass throughout life.

where it interacts with nuclear receptors to initiate protein swimmers “peaked” for the championships (weeks 18–24) in- synthesis. dicates long-term adaptation for these hormones, not the im- Plasma testosterone concentration in females, although mediate result of excess stress induced by overtraining and only one-tenth that in males, increases with physical activity. subsequent poor performance. The depressed performance Physical activity also elevates estradiol and progesterone levels. during weeks 18 through 24 might indicate overtraining; this In untrained males, resistance exercise and moderate aerobic period corresponded to a large increase in training volume. exercise increase serum and free testosterone levels after 15 to Chapter 21 provides an in-depth discussion of overtraining 20 minutes.72 Findings remain equivocal concerning the effect and its related syndrome. of intense endurance exercise on testosterone levels.128,157 FIGURE 20.15 shows the pattern of plasma cortisol and INTEGRATIVE QUESTION testosterone 48 hours before swimming and immediately fol- Hormones play crucial roles in normal growth lowing 15 200-m freestyle at the swimmer’s competitive and development and the regulation of velocity, with a 20-second rest between swims and 1 hour into physiologic function. Give specific examples of recovery. Four 6-week periods formed the training program, why more is not necessarily better for these with careful monitoring of training volume. The bar graphs chemicals. (right) show values for swim volume during the four training periods, including average performance during time trials. The results clearly show that postexercise cortisol and testosterone remain elevated. Values remained higher 1 hour after Pancreatic Hormones physical activity except for testosterone levels in training weeks 6 through 12 and 18 through 24. The generalized The pancreas gland, approximately 14-cm long and weighing decrease in cortisol and testosterone concentrations when the about 60 g, lies just below the stomach on the posterior 97818_ch20.qxd 8/4/09 11:56 PM Page 420

420 Section 3 Aerobic Systems of Energy Delivery and Utilization

280 60 )

260 –1 –1 240 k 40 w .

mL 220 . 20 200 km 180 0 160 140 –1) ortisol (ng 1.45 C

120 s 100 . 1.40 0

) 380 1.35 –1 360

mL 340 0 . 320 trial (m Time 300 7 280 260 5 240 220 3 200 Testosterone (ng Testosterone 0 Lactate (mM) 0 Before swim After swim 1h recovery Training period

(0—6 wk) (6—12 wk) (12—18 wk) (18—24 wk)

Figure 20.15 • Pattern of plasma cortisol and testosterone concentrations measured at three time intervals (4 h before swimming, immediately after multiple sprint swims, and after 1-h recovery) over a 24-week swim-training season. Bar graphs on right show values for swim volume, time-trial performance, and blood lactate during the four 6-week training periods. (Modified from Bonifazi M, et al. Blood levels of exercise during the training season. In: Miyashita M. et al., eds. Medicine and science in aquatic sports. Basel: Karger, 1994.)

abdominal wall. Two different types of tissues, acini and Following a meal, insulin-mediated glucose uptake by islets of Langerhans, named for German pathologist and cells (and correspondingly reduced hepatic glucose output) anatomist Paul Langerhans (1847Ð1888), who first described decreases blood glucose levels. In essence, insulin exerts a this cluster of cells in 1869 (FIG. 20.16), compose the pancreas. hypoglycemic effect by reducing blood glucose concentra- The islets are comprised of about 20% -cells that secrete tion. Conversely, with insufficient insulin secretion (or de- glucagon and 75% -cells that secrete insulin and a peptide creased insulin sensitivity), blood glucose concentration called amylin. The remaining cells are somatostatin-secreting increases from a normal level of about 90 mg dLÐ1 to a high D cells and PP cells that produce pancreatic polypeptide. of 350 mg dLÐ1. When blood glucose levels remain high, The acini serve an exocrine function and secrete digestive glucose ultimately spills into the urine. Without insulin, fatty enzymes. acids metabolize as the primary energy substrate. Insulin also exerts a pronounced effect on fat synthesis. A Insulin rise in blood glucose levels (as normally occurs following a meal) stimulates insulin release. This causes some glucose up- Insulin regulates glucose entry into all tissues (primarily take by fat cells for synthesis to triacylglycerol. Insulin’s action muscle and adipose) except the brain. Insulin’s action medi- also triggers intracellular enzyme activity that facilitates protein ates facilitated diffusion. In this process, glucose combines synthesis. This occurs by one or all of the following actions: with a carrier protein on the cell’s plasma membrane (see next 1. Increasing amino acid transport through the plasma section) for transport into cells. In this way, insulin regulates membrane glucose metabolism. Any glucose not immediately catabo- 2. Increasing cellular levels of RNA lized for energy either stores as glycogen or synthesizes to tri- 3. Increasing protein formation by ribosomes acylglycerol. Without insulin, only trace amounts of glucose enter the cells. FIGURE 20.17A illustrates that the anabolic func- Insulin Transport of Glucose into Cells: Glucose tions of insulin promote glycogen, protein, and fat synthesis; Transporters. Cells possess different glucose transport pro- FIGURE 20.17B outlines the target tissues and specific meta- teins (termed glucose transporters or GLUTs), depending on bolic responses to insulin’s action. the variation in insulin and glucose concentrations.97,135 Muscle 97818_ch20.qxd 8/4/09 11:56 PM Page 421

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 421

High blood sugar

Insulin stimulates glycogen formation to lower blood sugar

Insulin Glycogen Glucose Glucagon Pancreas Liver

Glucagon stimulates glycogen breakdown to raise blood sugar

Islets of Langerhans: Alpha cells (secrete glucagon) Insulin stimulates Beta cells (secrete insulin glucose uptake and amylin) from blood to lower Low blood blood sugar sugar Tissue cells

Acini cells (secrete digestive enzymes)

Figure 20.16 • The pancreas, its secretions, and their actions.

fibers contain GLUT-1 and GLUT-4, with most glucose entering catecholamine release on pancreatic -cell activity. by the GLUT-1 carrier during rest. With high blood glucose or Catecholamine suppression of insulin relates directly to physi- insulin concentrations (as occur after eating or during physical cal activity intensity. Physical activity inhibition of insulin out- activity), muscle cells receive glucose via the insulin-dependent put explains why no excessive insulin release (and possible GLUT-4 transporter. GLUT-4 action is mediated through a sec- rebound hypoglycemia) occurs with a concentrated glucose ond messenger, which permits migration of the intracellular feeding during physical activity. Prolonged physical activity GLUT-4 protein to the surface to promote glucose uptake. The derives progressively more energy from free fatty acids mobi- fact that GLUT-4 moves to the cell surface through a separate, lized from the adipocytes from reduced insulin output and de- insulin-independent mechanism coincides with observations creased carbohydrate reserves. Blood glucose lowering with that active muscles absorb glucose without insulin. prolonged physical activity directly enhances hepatic glucose output and sensitizes the liver to the glucose-releasing effects of glucagon and epinephrine, whose actions help to stabilize GlucoseÐInsulin Interaction. Blood glucose levels within blood glucose levels. the pancreas directly control insulin secretion. Elevated blood glucose levels cause insulin release. This, in turn, induces glucose entry into cells (lowers blood glucose), removing the Diabetes Mellitus. Diabetes mellitus consists of sub- stimulus for insulin release. In contrast, a decrease in blood groups of disorders with different pathophysiologies. The cur- glucose concentration dramatically lowers blood insulin lev- rent statistics regarding diabetes prevalence in the United els to provide a favorable milieu to increase blood glucose. States are staggering (see FIG. 20.19). Between 2003 and 2006, The interaction between glucose and insulin serves as a feed- 25.9% of the United States population 20 years and older had back mechanism to maintain blood glucose concentration diabetes; for those older than 60 years of age the prevalence within narrow limits. Rising levels of plasma amino acids was 34%. About 12.0 million, or 11.2%, of all men and 11.5 also increase insulin secretion. million, or 10.2%, of women aged 20 years or older have diabetes. Nearly 15 million, or 9.8%, of non-Hispanic whites and FIGURE 20.18 relates plasma insulin concentration to exercise duration for cycling at 70% VO2max. The inset graph 3.7 million, or 14.7%, of non-Hispanic blacks aged 20 years or older are diabetics. shows insulin response as a function of exercise intensity (%VO2max). The decreased insulin concentration (below From 2005 to 2007 there was an unprecedented 13.5% rest values) as exercise duration extends or intensity in- increase in diabetes prevalence; 2007 alone saw 1.6 million creases results from inhibitory effects of an exercise-induced newly diagnosed cases, which brought the total number of 97818_ch20.qxd 8/4/09 11:56 PM Page 422

422 Section 3 Aerobic Systems of Energy Delivery and Utilization A

Glucose Amino acids Blood Plasma membrane Cytoplasm

Glycogen Glucose

Glycolysis Mitochondrion

Citric Acid Actyl-CoA Pyruvate Cycle

Amino acids Electron transport ATP

Triacylglycerol Protein

B Increased Insulin Secretion

Most tissues Adipose tissue Liver and muscle Liver

Glucose uptake Fatty acid and Glycogen Fatty acid and (except brain, liver, triacylglycerol synthesis triacylglycerol exercising muscle) synthesis synthesis

Amino acid uptake Lipolysis Glycogenolysis Glycogenolysis

Protein synthesis

Protein breakdown

Figure 20.17 • A. Primary functions of insulin in the body. The ✪ show where insulin exerts its influence in metabolism. B. Target tissues and specific metabolic responses to insulin’s action. The anabolic functions of increased insulin promote glycogen, protein, and fat synthesis. 97818_ch20.qxd 8/4/09 11:56 PM Page 423

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 423

20 ) 1 – mL . 15

20 ) –1 16 mL . 10 12 8 Plasma insulin (μ units 0 25 50 75 100 Plasma insulin (μ units Percentage VO2max

5 0 5 10 15 20 25 30 Exercise duration (min)

Figure 20.18 • Plasma insulin levels during 30 minutes of cycle ergometer exercise at 70% VO2max. Inset, data show insulin concentrations related to exercise intensity (%VO2max). (From Applied Physiology Laboratory, University of Michigan, Ann Arbor.)

diabetics to 23.6 million men and women, or about 8% of the U.S. population, with at least another 10% undiagnosed. 25 Most importantly, roughly one-third of all new cases are 23.8% under the age of 20: Truly, diabetes has become a “childhood disease”! Diabetes is the seventh leading cause of death in the 20 United States and directly related to heart disease, hypertension, blindness, kidney failure, nervous system disease, am- putations, dental disease, complications of pregnancy, and 15 pneumonia, Additionally, over 90% of all diabetics are hope- lessly sedentary; they cannot walk continuously for a quarter mile or climb one flight of stairs!

Percentage 10.8% 10 Diabetes: A Global Epidemic and a Worldwide Healthcare Problem ¥ By 2025, the largest increases in diabetes preva- 5 lence will take place in developing countries. ¥ Every 10 seconds a person dies from diabetes- 2.6% related causes. 0 ¥ Every 10 seconds two people develop diabetes. 20–39 40–59 60+ ¥ Diabetes is the fourth leading cause of global Age group (y) death by disease. ¥ Diabetes currently affects 246 million people Figure 20.19 • Prevalence of diagnosed and undiagnosed worldwide and will affect 380 million by 2025. diabetes among people aged 20 years or older, United States, ¥ In 2007, the five countries with the largest num- 2007. Age 20 years or older: 23.5 million, or 10.7%, of all ber of diabetics were India (40.9 million), China people in this age group have diabetes. Age 60 years or (39.8 million), the United States (19.2 million), older: 12.2 million, or 23.8%, of all people in this age group Russia (9.6 million) and Germany (7.4 million). have diabetes. (From 2004–2006 National Health Interview Survey estimates projected to year 2007.) ¥ In 2007, the five countries with the highest diabetes prevalence in the adult population were 97818_ch20.qxd 8/4/09 11:56 PM Page 424

424 Section 3 Aerobic Systems of Energy Delivery and Utilization Nauru (30.7%), United Arab Emirates (19.5%), ¥ The clamp procedure involves maintaining insulin at Saudi Arabia (16.7%), Bahrain (15.2%), and a constantly above-normal blood concentration using Kuwait (14.4%). infusion technology (termed hyperinsulinemic ¥ Each year 3.8 million deaths are attributable to clamp). Once insulin stabilizes at the higher level, diabetes. An even greater number die from car- the body’s use of glucose is measured by infusing a diovascular disease made worse by diabetes- known amount of glucose into the patient’s blood. A related lipid disorders and hypertension. euglycemic clamp maintains blood glucose at near- ¥ At least 50% of all people with diabetes are un- normal concentration with insulin production mea- aware of their condition. In some countries this sured. A euglycemicÐhyperinsulinemic clamp figure reaches 80%. combines both clamp procedures. A large glucose ¥ 10% to 20% of people with diabetes die of renal uptake for a given insulin concentration reflects in- failure. creased insulin sensitivity. Increased insulin release ¥ More than 2.5 million people worldwide are to a constant glucose condition relates to augmented affected by diabetic retinopathy; it is the leading insulin responsiveness. Decreased insulin sensitivity cause of vision loss in adults of working age indicates inability of cells to adequately respond to (20 to 65 years) in industrialized countries. insulin to increase glucose uptake. Type 2 diabetes ¥ On average, people with type 2 diabetes die commonly reflects inadequacies in either insulin 5 to 10 years before people without this receptors or cellular response to insulin binding disease. (i.e., there is relative insulin resistance). Decreased ¥ Cardiovascular disease is the major cause of insulin responsiveness indicates impaired -cell death in diabetes, accounting for some 50% of function evident in some type 2 diabetics and is the all diabetes fatalities. primary cause of type 1 diabetes. [The term impaired ¥ Type 2 diabetics are over twice as likely to have fasting glucose (IFG) indicates fasting blood glucose a heart attack or a stroke as people without values are 100 mg dLÐ1 (5.6 mmol LÐ1), but diabetes. 126 mg dLÐ1 (7 mmol LÐ1).] Sources: ¥ Oral glucose-tolerance test evaluates blood sugar 1. Diabetes atlas, third edition, International levels 2 hours after drinking 75 grams of a concen- Diabetes Federation, 2007. trated glucose solution. Delayed removal of ingested 2. World Health Organization diabetes unit: glucose indicates diabetes. [The term impaired glu- www.who.int/diabetes. cose tolerance (IGT) indicates a 2-h glucose clearance between 140 mg dLÐ1 (7.8 mmol LÐ1) but 200 mg dLÐ1 (11.1 mmol mLÐ1).] ¥ Fasting plasma glucose (FPG) test measures plasma The terms type 1 (absolute insulin deficiency that devel- glucose following an 8-hour fast. The American ops early in life and represents 5% to 10% of the diabetic pop- Diabetes Association (http://www.diabetes ulation) and type 2 (relative insulin resistance and deficiency .niddk.gov/) currently recommends the FPG test. that develops later in life and associates with obesity, diet, and sedentary living) identify the two major diabetic subgroups. Diabetes symptoms include: Classification Categories for Fasting ¥ Presence of glucose in the urine (glycosuria) Blood Glucose ¥ Frequent urination (polyuria) ¥ Excessive thirst (polydipsia) Category Fasting Plasma Glucose ¥ Extreme hunger (polyphagia) Normal 110 mg dL1 ¥ Unexplained weight loss Impaired range 110Ð125 mg dL1 ¥ Increased fatigue Suspected diabetes 125 mg dL1 ¥ Irritability ¥ Blurry vision ¥ Numbness or tingling in the extremities (hands, feet) ¥ Slow-healing wounds or sores Considerable risks exist for impaired glucose ¥ Abnormally high frequency of infection homeostasis—probably a genetic trait that manifests itself in adolescence—in which blood glucose remains elevated, but Use the following Internet site to calculate your diabetes not high enough for diabetic classification. Nondiabetic, risk: www.diabetes.org/risk-test.jsp. middle-aged men whose FPG falls in the upper range of nor- Tests for Diabetes Mellitus. Different tests diagnose dia- mal show a higher risk of death from heart disease than betes, including the laboratory-based glucose and insulin those in the lowÐnormal range.7 Men with fasting blood glu- clamp methodology, an oral glucose-tolerance test, and a sim- cose levels above 85 mg dL1 have a 40% higher risk of ple 8-hour fasting plasma glucose test. cardiovascular death than men with lower values, even 97818_ch20.qxd 8/4/09 11:56 PM Page 425

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 425 after adjusting for age, smoking habits, blood pressure, and and women.41 The age-adjusted prevalence is similar for men fitness status. The current plasma glucose cutoff for sus- (24%) and women (23.4%). Mexican Americans have the 1 pected diabetes is an FPG of 126 mg dL , down from the highest age-adjusted prevalence of the syndrome (31.9%). The 1 previous standard of 140 mg dL set in 1979. This lower lowest prevalence occurs among whites (23.8%), African cutoff acknowledges that patients can remain asymptomatic Americans (21.6%), and people reporting “other” for race or despite microvascular complications (damaged small blood ethnicity (20.3%). Among African Americans, women exhibit 1 vessels) with FPG values in the low- to mid-120 mg dL a 57% higher prevalence than men; Mexican American range. The impaired range represents a transition between women have a 26% higher prevalence. normal and overt diabetes. In this situation, the body no This “disease of modern civilization” afflicts a large longer responds properly to insulin and/or secretes inade- number of adults (more common in men than women) in quate insulin to achieve a more desirable blood glucose western industrialized countries. Disease occurrence relates concentration. to genetic, hormonal, and lifestyle factors of obesity, physical inactivity, and nutrient excesses, including high intakes of saturated and trans-fatty acids. Although characterized by the Metabolic Syndrome clustering of insulin resistance and hyperinsulinemia, dyslipi- Metabolic syndrome, first mentioned in the late 1980s, rep- demia (atherogenic plasma lipid profile), essential hyperten- resents a multifaceted grouping of coronary artery disease sion, abdominal (visceral) obesity, and glucose intolerance, risks.9,41,92 Diet-induced insulin resistance/hyperinsulinemia the syndrome also relates to abnormalities of blood coagula- often occurs before manifestations of the metabolic syndrome tion, hyperuricemia, and microalbuminuria. Psychosocial stress, socioeconomic disadvantage, and abnormal psychi- of obesity, insulin resistance, glucose intolerance, dyslipi- 8,9 demia, and hypertension.4,110,144 In essence, the syndrome re- atric traits also link to the syndrome’s pathogenesis. flects a concurrence of four factors: TABLE 20.4 provides percentage body fat ranges and associated risk equivalent to the traditional BMI cutoffs for the 1. Disturbed glucose and insulin metabolism (fasting metabolic syndrome for black and white men and women. glucose 110 mg dL1) Lifestyle modifications that include increased regular physi- 2. Overweight with abdominal fat distribution (waist cal activity represent the cornerstone of national recommen- circumference: men 102 cm [40 in]; women dations to prevent the metabolic syndrome.110,175 88 cm [35 in]) 1 3. Mild dyslipidemia (triacylglycerols 150 mgádL ; Insulin Actions and Impaired high-density lipoprotein cholesterol: men, 40 mg dL1; women 50 mg dL1 Glucose Homeostasis 4. Hypertension (130/85 mm Hg) FIGURE 20.20 summarizes insulin’s normal response and under insulin-resistant and type 2 diabetes conditions. The increase in blood glucose concentration following a meal induces insulin re- Common Characteristics of the Metabolic lease from the -cells in the islets of Langerhans. Insulin then Syndrome migrates in the blood to target cells throughout the body, where it Insulin resistance binds to receptor molecules on the cell surface. InsulinÐreceptor Glucose intolerance interaction triggers a series of events within the cell that enhance Dyslipidemia (high triacylglycerols, low HDL, glucose uptake and subsequent catabolism or storage as glyco- high LDL) gen and/or fat. A defect anywhere along the pathway for glucose Stroke uptake signals diabetes. Seven possible causes include: Upper-body obesity Type 2 diabetes mellitus 1. Destruction of -cells 2. Abnormal insulin synthesis Hypertension 3. Depressed insulin release Coronary artery disease 4. Inactivation of insulin in the blood by antibodies or Reduced ability to dissolve blood clots other blocking agents 5. Altered insulin receptors or a decreased number of Individuals with metabolic syndrome exhibit high risk for receptors on peripheral cells cardiovascular disease, type 2 diabetes, Alzheimer’s disease, 6. Defective processing of the insulin message within and all-cause mortality.91 Some researchers maintain that inap- the target cells propriate food consumption (high levels of refined sugars), 7. Abnormal glucose metabolism sedentary lifestyle, and poor levels of muscular strength and cardiorespiratory fitness not only associate with the metabolic Type 1 Diabetes syndrome but represent features of this disease.75,90,132 Estimates place the age-adjusted prevalence of the metabolic syndrome Type 1 diabetes, formerly called juvenile-onset dia- in the United States at nearly 25%, or about 47 million men betes, typically occurs in younger individuals and represents 97818_ch20.qxd 8/4/09 11:56 PM Page 426

426 Section 3 Aerobic Systems of Energy Delivery and Utilization

TABLE 20.4 • Thresholds of Percentage Body Fat (%BF) Corresponding to Established Body Mass Index Cutoffs Associated with Metabolic Syndrome Risk

%BF and Corresponding Percentiles Men Women BMI Black White Black White Cutoffs (KG/M2) Cutoff Percentile Cutoff Percentile Meana Cutoff Percentile Cutoff Percentile

18.5 12.7 8.9 11.0 3.9 12 25.4 11.7 22.5 24 25 21.7 43.5 21.2 41.0 21 32.0 29.3 30.8 31 30 28.3 80.9 29.1 87.6 29 37.1 52.5 37.2 37 35 35.0 97.6 37.0 99.4 36 42.1 75.9 43.5 43

aValues were rounded. From Zhu S, et al. Percentage body fat ranges associated with metabolic syndrome risk: results based on the third National Health and Nutrition Examination Survey (1988Ð1994). Am J Clin Nutr 2003;78:228.

between 5 and 10% of all diabetes cases. This diabetes form (up to 80% of type 2 diabetes are obese), aging, and possibly a represents an autoimmune response, possibly from a single high-fat diet. No doubt, these lifestyle factors have contributed protein that renders the -cells incapable of producing in- to the 70% increase in the disorder among persons in their 30s sulin and often other pancreatic hormones. Type 1 diabetic during the last decade of the 20th century, and a 33% overall patients present a more severe abnormality for glucose increase nationally. Also, the form of insulin resistance in type homeostasis than individuals in the type 2 subgroup. 2 diabetes has a strong genetic component. Diabetic-prone in- Physical activity exerts more pronounced effects on the dividuals possess a gene that directs synthesis of a protein that metabolic state in type 1 individuals, and the management of inhibits insulin’s action in cellular glucose transport. exercise-related problems requires greater attention (see “In a Practical Sense,” p. 428). Risk Factors for Type 2 Diabetes Type 2 Diabetes ¥ Body mass exceeds 20% of ideal Type 2 diabetes tends to occur after age 40, but a sharp in- ¥ First-degree relative with diabetes (genetic crease now occurs in much younger individuals (often less influence) than 10 years of age). This alarming new health trend signals ¥ Member of a high-risk ethnic group (black, that type 2 diabetes may represent a “pediatric disease.” Hispanic American, Pacific Islander, American Recent estimates indicate that diabetes has more than tripled in Indian, Asian) children over the last 3 to 5 years. Physicians consider the spi- ¥ Delivered a baby weighing more than 9 pounds raling rate of childhood obesity—particularly among African or developed gestational diabetes Americans, Native Americans, and Hispanics (most notably ¥ Blood pressure at or above 140/90 mm Hg children of Mexican descent)—as the predominant factor in ¥ HDL cholesterol level of 35 mg dL 1 or below the rising number of children with type 2 diabetes. Type 2 dia- and/or a triacylglycerol level of 250 mg dL 1 betes accounts for nearly 95% of all diabetes cases in the or above United States; it represents the leading cause of death from the ¥ Impaired fasting plasma glucose or impaired disease. Treatment costs exceed $105 billion annually. glucose tolerance on previous testing Three factors can produce high blood glucose levels in type 2 diabetes: Obesity, particularly upper-body fat distribution, and 1. Inadequate insulin produced by the pancreas to con- physical inactivity represent major risks for type 2 diabetes trol blood sugar (relative insulin deficiency) in adults and children.164 An estimated 60 to 80 million 2. Decreased insulin effects on peripheral tissue (insulin Americans show insulin resistance but have not developed resistance), particularly skeletal muscle (Fig. 20.20) overt symptoms of type 2 diabetes. One-third of these indi- 3. Combined effect of factors 1 and 2 viduals will eventually become full-blown diabetics, and A dysregulation in glycolytic and oxidative capacities of many others are at heightened risk of cardiovascular disease.52 skeletal muscle also relates to insulin resistance in type 2 dia- Failure of insulin to exert its normal effect increases glucose betes.143 The disease most likely results from the interaction of conversion to triacylglycerol and storage as body fat. For the genes and lifestyle factors—physical inactivity, weight gain insulin-resistant individual, a diet high in simple sugars and 97818_ch20.qxd 8/4/09 11:56 PM Page 427

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 427

Insulin Beta cells of pancreas Muscle fiber Receptor Increase in plasma membrane Transport Messenger Plasma molecule permeability glucose Enzyme G G activation Metabolic G effect G Energy release Insulin release and/or macronutrient Insulin synthesis

G G A Normal response G The rise in blood glucose G after eating stimulates insulin release from the beta cells of the pancreas. G Insulin mediates facilitated G diffusion into the cell where glucose combines with a carrier on G the plasma membrane of muscle G G and adipose tissue cells. Any G glucose not immediately G catabolized for energy stores as Muscle glycogen or synthesizes to fat for Capillary fiber later use.

B Insulin-resistant response

The pancrease overproduces insulin (abnormal output) in response to a rise in blood glucose G as occurs from the rapid digestion G and absorption of some dietary G starches and simple sugars. Excess insulin production maintains blood glucose at the G upper level of the normal range. Thus, the person does not classify as a type 2 diabetic. However, a G chronic high insulin output in G G response to elevations in blood glucose after eating strongly relates to the metabolic syndrome of dyslipidemia, hypertension, upper-body obesity, and increased risk for heart attack and stroke.

C Type 2 diabetes G G G The pancreas continues to secrete G G insulin. However, the severity of G insulin resistance exceeds the G pancreas' maximum insulin output G to regulate blood glucose within the normal range. This results in the diagnosis of type 2 diabetes. G G G G

Figure 20.20 • A. Normal insulin–glucose interaction, B. with insulin resistance, and C. type 2 diabetes. 97818_ch20.qxd 8/4/09 11:56 PM Page 428

428 Section 3 Aerobic Systems of Energy Delivery and Utilization

IN A PRACTICAL SENSE Diabetes, Hypoglycemia, and Physical Activity

Persons with type 1 or type 2 diabetes should exercise regularly as ¥ If exercise lasts beyond 45 minutes, monitor blood glu- part of a comprehensive treatment regimen. Hypoglycemia repre- cose at 2-hour intervals for 12 hours into recovery or until sents the major risk of physical activity for individuals who take in- sleep. Consider reducing insulin or oral hypoglycemic sulin or oral hypoglycemic agents. A physically active diabetic agents until bedtime. Before retiring, eat some low- person needs to pay particular attention to the following: glycemic food to increase blood glucose levels. ¥ Use caution when initiating a physical activity program. 1. Warning signs of hypoglycemia Start slowly and gradually increase exercise intensity and 2. Immediate response to a hypoglycemia attack duration over a 3- to 6-week period. 3. Treatment of late-onset hypoglycemia ¥ If planning to exercise longer than 45 to 60 minutes, HYPOGLYCEMIA WARNING SIGNS exercise with a friend who can assist in an emergency. Always carry snacks and important phone numbers Symptoms of moderate and severe hypoglycemia (see Table) result (doctor, hospital, home), and wear a medical ID from inadequate glucose supply to the brain. In general, hypo- bracelet. glycemic symptoms appear only after blood glucose concentration drops below 60 mg dL 1. Symptoms of low blood glucose vary considerably. Some dia- ADJUSTING INSULIN LEVELS betic persons with autonomic neuropathy who lose the ability to For intense physical activity, consider the following: secrete adrenaline-like hormones in response to hypoglycemia experience hypoglycemic unawareness. They require regular blood glu- ¥ Intermediate-acting insulin: Decrease dose by 30 to 35% cose monitoring during and after physical activity. Individuals who on the day of exercise. take -blocker medication also have increased risk for hypo- ¥ Intermediate- and short-acting insulin: Omit dose if it glycemic unawareness. normally precedes physical activity. ¥ Multiple doses of short-acting insulin: Reduce dose before HYPOGLYCEMIA ATTACK: WHAT TO DO exercise by 30% and supplement with carbohydrate-rich 1. Respond quickly: Hypoglycemic reactions appear suddenly food. and progress rapidly. ¥ Continuous subcutaneous insulin infusion: Eliminate meal- 2. Stop exercising: Test blood glucose to confirm time bolus or insulin increment that precedes or follows hypoglycemia. physical activity. 3. Eat or drink carbohydrate: Immediately consume 10 to 15 g ¥ Avoid exercising for 1 hour the muscles that receive the of simple sugar. A diabetic person should always carry high- short-acting insulin injection. glycemic carbohydrate while exercising (e.g., hard candy, ¥ Avoid exercising in late evening. sugar cubes, raisins, juice). Consuming ice cream or choco- lates is a poor choice; their high fat content depresses the glycemic index and impedes glucose absorption. 4. Rest 10 to 15 minutes: This allows for intestinal absorption of glucose. Test blood glucose levels before resuming physical activity. If blood glucose registers below 100 mg dL 1, do not exercise but eat more sugar. Warning Signs of Hypoglycemia 5. Remonitor during physical activity: After resuming physical ac- Mild hypoglycemic reaction tivity, pay close attention to further signs of hypoglycemia. If possible, measure blood glucose within 30 to 45 minutes. ¥ Trembling or shakiness 6. Replenish carbohydrate immediately after physical activity: ¥ Nervousness Consume complex carbohydrates. If carbohydrate intake ¥ Rapid heart rate does not increase blood glucose concentration, be pre- ¥ Palpitations pared to administer glucagon subcutaneously to boost ¥ Increased sweating glucose levels. ¥ Excessive hunger Moderate hypoglycemic reactions LATE-ONSET HYPOGLYCEMIA Late-onset hypoglycemia describes the condition of excessively low ¥ Headache blood glucose more than 4 hours (and up to 48 h) after physical ac- ¥ Irritability and abrupt mood changes tivity. It occurs more frequently in new exercisers or after a strenu- ¥ Impaired concentration and attentiveness ous workout. Insulin sensitivity remains high for 24 to 48 hours ¥ Mental confusion after physical activity, so late-onset hypoglycemia poses a particular ¥ Drowsiness problem for many medicated diabetics. The following precautions Severe hypoglycemic reactions can guard against late-onset hypoglycemia: ¥ Unresponsiveness ¥ Adjust insulin dosage or other medication before exercis- ¥ Unconsciousness and coma ing. If needed, increase food intake before and during ¥ Convulsions physical activity. 97818_ch20.qxd 8/4/09 11:56 PM Page 429

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 429 refined carbohydrates (with a relatively high glycemic index) INTEGRATIVE QUESTION facilitates body fat accumulation. Fat cell enlargement further Explain the sweet-smelling breath of individuals exacerbates the situation because these cells exhibit insulin who suffer from poorly regulated diabetes resistance from their reduced insulin receptor density. mellitus or malnutrition from starvation. Interestingly, women with excess body fat and high cardiorespiratory fitness are more insulin sensitive than equally obese but sedentary counterparts.44 Glucagon Characteristics of Type 1 and Type 2 Diabetes The -cells of the islets of Langerhans secrete glucagon, the “insulin antagonist” hormone. In contrast to insulin’s ef- Type 1 Type 2 fect in lowering blood sugar levels, glucagon primarily stimu- Characteristics Diabetes Diabetes lates both glycogenolysis and gluconeogenesis by the liver Age of onset Usually 20 y Usually and increases lipid catabolism. (FIG. 20.21). The glucose 40 y (but generated by glucagon action then moves into the blood. increasing Glucagon exerts its effect by activating adenylate cyclase. in children) This enzyme stimulates cyclic AMP in liver cells and causes Proportion of 10% 90% all diabetics hepatic glycogen breakdown to glucose (glycogenolysis). Appearance Acute or Slow Glucagon also stimulates gluconeogenesis by promoting the of symptoms subacute liver’s uptake of amino acid uptake. Metabolic Frequent Rare As with insulin, plasma glucose concentration controls ketoacidosis glucagon output by the pancreas. A decrease in blood glucose Obesity at onset Uncommon Common -cells Decreased Variable concentration from prolonged intense physical activity or food Insulin Decreased Variable (or carbohydrate) restriction stimulates glucagon release. Inflammatory Present initially Absent Autonomic nervous stimulation does not mediate cells in islets glucagon release, unlike its effects on insulin secretion. Also, Family history Uncommon Common no gender differences exist in the glucagon response to exercise when individuals exercise at the same percentage of aerobic capacity.29,154 Because glucagon release occurs later in exercise, this hormone exerts little influence in the early regu- As with type 1 diabetes, adequate glucose fails to enter lation of hepatic glycogenolysis. More than likely, it primarily the cells of a person with type 2 diabetes. This triggers abnormally high levels of blood glucose that the kidney tubules fil- ter and void in the urine (glycosuria). Excessive glucose Increased Glucagon Secretion particles in renal filtrate create an osmotic effect that diminishes water reabsorption, which results in loss of large amounts of fluid (polyuria). With decreased cellular glucose uptake, a diabetic person relies largely on fat catabolism for energy. This produces an excess of ketoacids and a tendency toward acidosis. In extreme situations, diabetic coma occurs as plasma pH falls as low as 7.0. Arteriosclerosis, small blood vessel and nerve disease, and susceptibility to infection occur at increased rates in type 2 diabetes. Obese diabetic women also face an almost threefold greater risk of endometrial can- Liver Adipose tissue cer than diabetic women of normal weight, perhaps from their persistently high insulin levels (insulin insensitivity).140

Diabetes and Physical Activity. Hypoglycemia remains the most common disturbance in glucose homeostasis during Glycogenolysis Lipolysis physical activity in diabetic persons who take exogenous insulin. Hypoglycemia most frequently occurs during pro- Glycogen synthesis Triacylglycerol synthesis longed, intense physical activity when hepatic glucose release Gluconeogenesis does not match increased glucose use by active muscle. In ad- Ketone synthesis dition, persons with type 2 diabetes often have reduced exer- Protein breakdown cise tolerance independent of glycemic control. Contributing factors include genetics, undesirable lifestyle characteristics, Figure 20.21 • Glucogen secretion and its action on target excessive body fat, and poor physical fitness. tissues. 97818_ch20.qxd 8/4/09 11:56 PM Page 430

430 Section 3 Aerobic Systems of Energy Delivery and Utilization contributes to blood glucose regulation as exercise progresses Improved target tissue sensitivity and/or responsiveness to a and glycogen reserves deplete. given amount of hormone accounts for much of this “efficiency” in response.26,65 A similar level of hormonal response Other Glands and Hormones occurs regardless of training state when subjects exercise at the same relative exercise intensity (i.e., same percentage of Other hormones also influence bodily functions. The liver se- maximum [lower absolute load for the untrained]). With max- cretes somatomedins, which affect growth of muscle, carti- imal exercise, trained subjects have an identical or somewhat lage, and other tissues. The mucosal lining of the small greater hormonal response than untrained subjects. intestine secretes secretin, gastrin, and cholecystokinin to promote and coordinate digestive processes. The hypothalamus itself constitutes an important endocrine gland that Anterior Pituitary Hormones secretes stimulating or releasing hormones that activate or release anterior pituitary hormones. The hypothalamus also Growth Hormone releases somatoliberin, which stimulates somatotropin secre- GH stimulates lipolysis and inhibits carbohydrate break- tion from the anterior pituitary gland. down, so some have argued that exercise training enhances GH secretion and conserves glycogen reserves. However, this EXERCISE TRAINING AND does not occur. Compared with untrained counterparts, endurance-trained individuals show less rise in blood GH levels ENDOCRINE FUNCTION at a given physical activity intensity—a response attributed to TABLE 20.5 lists select hormones and their general response to reduced exercise stress as training progresses and fitness im- exercise training. Only limited research has evaluated multiple proves. Regardless of training status, women typically main- hormone secretions and changes consequent to exercise train- tain higher GH levels at rest than men; this difference 17 ing because of the complex interactions between endocrine se- disappears during prolonged exercise. FIGURE 20.22A illus- cretions and the nervous system. The magnitude of hormonal trates the training-induced depression of GH response of a response to a standard exercise load generally declines with representative subject from a group of six men during 20 min- endurance training. For example, when highly trained athletes utes of constant-load, intense exercise before and after 3 and perform at the same absolute exercise level as sedentary 6 weeks of endurance training. Integrated GH concentrations subjects, hormonal responses remain lower in the athletes. (exercise plus recovery) for the group averaged 45% lower

TABLE 20.5 • Hormones and Their Responses to Endurance Training

Hormone Training Response

Hypothalamus-pituitary hormones Growth hormone No effect on resting values; less dramatic rise during exercise Thyrotropin No known training effect ACTH Increased exercise values Prolactin Some evidence that training lowers resting values FSH, LH, and testosterone Trained females have depressed values; reduced testosterone in males (testosterone levels may increase in males with long-term resistance training) Posterior pituitary hormones Vasopressin (ADH) Slightly reduced ADH at a given workload Oxytocin No research results available Thyroid hormones

Thyroxine (T4) Reduced concentration of total T3 and increased free thyroxine at rest Triiodothyronine (T3) Increased turnover of T3 and T4 during exercise Adrenal hormones Aldosterone No training adaptation Cortisol Slight elevation during exercise Epinephrine and norepinephrine Decreased secretion at rest and at the same absolute exercise intensity after training Pancreatic hormones Insulin Increased sensitivity to insulin; normal decrease in insulin during exercise greatly reduced with training Glucagon Smaller increase in glucose levels during exercise at absolute and relative workloads Kidney enzyme and hormone Renin and angiotensin No apparent training effect 97818_ch20.qxd 8/4/09 11:56 PM Page 431

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 431 than pretraining values at both training measures. Responses Pre-training Week 3 Post-training for plasma catecholamines (FIG. 20.22B AND C) and blood lactate (FIG. 20.22D) paralleled the decrease in GH. Because the 5 constant-load exercise test represented less physiologic demand after training (reflected by lower catecholamine and 4 lactate levels), a similar release of GH after training probably ) requires higher absolute exercise intensity. The effect of exer- –1 3 L

. cise training on GH release also may occur under nonexercise 2 conditions. For example, aerobic training above the lactate (μg w th hormone threshold level amplifies the 24-hour pulsatile GH release ro 1 G during rest (see “Focus on Research,” p. 433). 0 5152535 45 55 65

Exercise Recovery ACTH (Adrenocorticotropic Hormone) (0-20 min) (20-65 min) ACTH secreted by the posterior pituitary gland provides potent stimulation to the adrenal cortex and thus increases 400 free fatty acid mobilization for energy. Training increases ACTH release during physical activity—a response that stim- H 300 ulates adrenal gland activity to promote fat catabolism and 13, 95

x min) spare glycogen. This effect would certainly benefit pro-

–1 200 longed, high-intensity exercise performance. L . **

Integrated G Integrated 100 (μg PRL (Prolactin) 0 A Pre Week 3 Post Little information exists concerning exercise training changes in PRL. It does appear that resting PRL levels of male ) 4 runners average below values for sedentary nonrunners.54,167 –1 L . 3 FSH (Follicle-Stimulating Hormone), LH 2 (Leuteinizing Hormone), and Testosterone Regular physical activity depresses reproductive hor- 1 ** 33,168 (in thousands) mone responses in women and men. Male endurance athletes generally maintain resting testosterone levels between

Epinephrine (pmol 0 60 and 85% of values for sedentary men. B Pre Week 3 Post 30 Women. Women with a long history of exercise participation have altered FSH and LH levels at different times in )

–1 20 their menstrual cycles, which may contribute to menstrual L

. dysfunction. For example, FSH levels remain depressed in ** trained females throughout an abbreviated anovulatory men- 10 strual cycle, whereas LH and progesterone concentrations rise (nmol

Norepinephrine in the cycle’s follicular phase. Variations in the menstrual 0 C Pre Week 3 Post 15 Figure 20.22 • Top. Serum growth hormone (GH) concentrations in a representative subject during 20 minutes of constant-load exercise and 45 minutes of recovery at 10 pretraining, after 3 weeks of training, and after 6 weeks of * training. Bottom. Effects of 6 weeks of training on integrated (mM) 5 ** GH concentration (A), and end-exercise concentrations of epinephrine (B), norepinephrine (C), and blood lactate (D) in Blood lactate response to constant-load cycle ergometry exercise (n 6, 0 D Pre Week 3 Post mean). Pre-week 3, after 3 weeks of training; Post, after 6 weeks of training. * P .05 versus pretraining; ** P .05 versus week 3. (From Weltman A, et al. Exercise training decreases the growth hormone (GH) response to acute constant-load exercise. Med Sci Sports Exerc 1997;29:669.) 97818_ch20.qxd 8/4/09 11:56 PM Page 432

432 Section 3 Aerobic Systems of Energy Delivery and Utilization cycle do not affect metabolic and hormonal responses to acute action that ultimately leads to hyperthyroidism (i.e., over- 43,76 bouts of physical activity. production of T3 and T4 hormones). However, no evidence indicates a higher incidence of hyperthyroidism in highly Men. Endurance training affects a man’s pituitaryÐ trained individuals. For example, inordinately high BMR lev- gonadal function, including levels of testosterone and PRL. els and basal body temperatures rarely occur in the trained FIGURE 20.23 compares 46 male runners (average weekly run- state. Consequently, the greater T4 turnover that accompanies ning distance: 64 km) and 18 nonrunners matched for age, physical training occurs through a mechanism that differs stature, and body mass. The runners showed lower testosterone from “normal” thyroid hormone dynamics. than nonrunners, with no differences in LH and FSH levels. Research on women who endurance train yields interest- Reduced testosterone concentration (both increased clearance ing results regarding thyroid turnover. Changing from a base- and lower production) in endurance-trained men parallels the line of relatively sedentary living to running 48 km per week sex-steroid reductions observed in women who undergo en- produced a mild thyroid impairment reflected by decreased T3 149 14 durance training and associated reductions in body fat. No and T4 levels. In contrast, nearly doubling the weekly dis- difference exists in LH and FSH levels between trained and un- tance increased plasma hormone levels. To explain these ap- trained men; thus, impaired gonadotropin release from the ante- parent conflicting effects of regular physical activity, the rior pituitary does not cause the lower testosterone levels researchers suggested that greater body fat loss with more in- during standard physical activity in the trained state. tense training produced an exercise-induced increase in thyroid output. Six months of resistance training in men slightly Posterior Pituitary Hormones reduced the concentrations of T4 and plasma-free T4, without change in TSH. However, the magnitude of the change was of ADH (Antidiuretic Hormone) no clinical or physiologic significance.124 Intense physical activity to exhaustion or prolonged submaximal activity at the same relative intensity produces no Adrenal Hormones difference in ADH levels between trained and untrained individuals. ADH concentration decreases with training when ex- Aldosterone ercising at the same absolute submaximal intensity. The reninÐangiotensinÐaldosterone system contributes to homeostatic control of body fluid volumes, electrolytes, PTH (Parathyroid Hormone) and blood pressure, but exercise training does not affect resting levels of these compounds or their normal response to Endurance training enhances exercise-related increases in physical activity. PTH in young and elderly adults.137,176 The significance of a training-induced augmented rise in PTH for preserving bone Cortisol mass with aging awaits further study. Plasma cortisol levels increase less in trained subjects Thyroid Hormones than in sedentary subjects who perform the same absolute level of submaximal exercise. Adrenal gland enlargement re- Exercise training produces a coordinated pituitaryÐthyroid results from both cellular hypertrophy and hyperplasia with sponse that reflects increased turnover of thyroid hormones. repeated bouts of intense exercise training and correspond- Increased thyroid turnover often reflects excessive hormonal ingly high cortisol output.

Testosterone Luteinizing hormone Follicle-stimulating (LH) hormone (FSH) 1000 12 8 –1 –1

–1 750 9 6 mL mL dL . . . 500 6 4 ng Imμ Imμ 250 3 2

0 0 0

Controls Runners

Figure 20.23 • Comparison of testosterone, LH, and FSH levels in trained male runners and untrained controls. Runners show lower testosterone levels than controls and no significant difference in LH and FSH. (From Wheeler GD, et al. Reduced serum testosterone and prolactin levels in male distance runners. JAMA 1984;252:514.) 97818_ch20.qxd 8/4/09 11:56 PM Page 433

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 433

FOCUS ON RESEARCH Training Intensity Affects Growth Hormone Release

Weltman A, et al. Endurance training amplifies the investigators speculated that the release of endogenous pulsatile release of growth hormone: effects of train- opiates and catecholamines and inhibition of somatostatin ing intensity. J Appl Physiol 1992;72:2188. release in more intense exercise performed by the LT group facilitated GH release. ➤ Research has focused on growth hormone (GH) re- This research showed that exercise training augments sponses to a single session of physical activity and long- resting pulsatile GH release by amplitude enhancement, term training. The dynamics of GH secretions during but only with training intensity above LT. Training at in- exercise training takes on clinical importance because of tensities above the LT may provide a natural and healthful the causal relationship between GH availability and main- means to increase pulsatile GH secretion under conditions tenance of lean body tissue during aging and weight loss. that depress GH release, as in aging. Increased GH release Weltman and colleagues studied GH dynamics with 52 through regular physical activity can conserve the lean tis- weeks of aerobic run training in two groups of 21 healthy, sue mass during weight loss. eumenorrheic women. One group ran at a speed corresponding to lactate threshold (@LT) and the other at a faster speed above the lactate threshold level (LT). Nontraining women served as controls (C). Both training groups com- 10,000 pleted similar weekly mileage. The distance covered during the first week was 5 miles. Weekly mileage then 9000 gradually increased to 24 miles by week 20 and continued at 24 miles per week until week 40. Thereafter, weekly 8000 )

mileage increased by 1.25 miles for three of the weeks. –1 7000 Subjects ran between 35 and 40 miles per week by the end H concentrations min . of the study. 6000 Yearlong training increased VO2max by 9.9% for the –1 L . 5000 @LT group and 11.8% for the LT group. In addition,

the @LT group increased exercise VO2 at LT (VO2-LT) by (μg 4000 21.5%, while the LT group’s VO2-LT increased by 28%. The C group remained unchanged on all measures. No 3000 differences in body mass, fat mass, or percentage body Integrated (24-h) G Integrated 2000 fat emerged within or among groups, although the LT Baseline 1 year group showed a trend toward body fat reduction. Both Time exercise groups increased fat-free body mass with training. > LT @ LT C The figure illustrates the effects of the run training program on resting 24-hour integrated serum GH concen- Integrated 24-hour resting GH concentrations for the control group trations. Training induced a 50% increase in resting GH (C) and groups that exercised either at an intensity equivalent to the lactate threshold (@LT) or greater than the lactate threshold (LT). Note the large concentration for the LT group. GH concentrations (50%) increase in GH concentration for the LT group compared with the remained unchanged for the C and @LT groups. The @LT and C groups.

Epinephrine and Norepinephrine reflect favorable adaptations because they lower myocardial oxygen demands during physical activity and possibly other Sympathoadrenal activity (principally norepinephrine forms of stress. For equivalent relative exercise intensities, a release) in response to an absolute submaximum workload re- 36 higher sympathoadrenal response occurs following aerobic mains lower in trained than untrained individuals. 51 training. FIGURE 20.24 illustrates norepinephrine and epi- Epinephrine and norepinephrine output in standard exercise nephrine during physical activity at intensities that ranged be- falls dramatically during the first several weeks of training. tween 60 to 85% of aerobic capacity by three adult men and The appearance of bradycardia and a smaller rise in blood six women prior to and following 10 weeks of aerobic train- pressure during submaximal exercise represent the most fa- ing that increased VO2max by 20%. Plasma norepinephrine miliar consequences of the sympathoadrenal training adapta- levels (Fig. 20.24, top) increased progressively with exercise tion. Reductions in exercise heart rate and blood pressure 97818_ch20.qxd 8/4/09 11:56 PM Page 434

434 Section 3 Aerobic Systems of Energy Delivery and Utilization )

3500 ) 250 –1 –1 3000

mL 200 . min 2500 . 2000 150 1500 100 1000

500 50 Plasma norepinephrine

concentration (pg concentration 0 0 ) 300 –1 )100 Plasma glucagon (pg 250 –1 mL . mL 200 . 80 150

100

50 60 Plasma epinephrine 0 concentration (pg concentration rest 60 65 70 75 80 85

Percentage VO Plasma insulin (μunits 0 2max 0102030 Exercise duration (min) Untrained Trained Pre-training Figure 20.24 • Plasma norepinephrine (top) and epinephrine Post-training concentrations (bottom) at rest and after 15 minutes of Figure 20.25 • Pre–post differences in plasma glucagon and exercise at the same relative exercise intensity (%VO ) 2max insulin responses to exercise before and after 20 weeks of an before and after 10 weeks of endurance exercise training. aerobic training program. (From Applied Physiology (From Greiwe JS, et al. Norepinephrine response to exercise at Laboratory, University of Michigan.) the same relative intensity before and after endurance training. J Appl Physiol 1999;86:531.)

intensity before and after training. Training produced higher from rest through light to moderately intense physical activity. plasma norepinephrine levels, particularly at higher intensi- FIGURE 20.25 shows insulin and glucagon responses in 10 young ties. Consistently higher epinephrine values also emerged fol- adults before and after 20 weeks of training at 60 to 80% lowing training (Fig. 20.24, bottom), but the differences did VO2max. Aerobic training depressed the exercise response of not reach statistical significance. More than likely, greater both hormones, with glucagon showing the most pronounced catecholamine output at the same relative exercise intensity reduction. These findings agree with previous reports for adults following training reflects three factors requiring greater sym- who trained for 10 weeks by running and cycling.53 pathetic nervous system activation: 1. Greater absolute demand for substrate use via Regular Physical Activity glycogenolysis and lipolysis and Type 2 Diabetes Risk 2. Increased overall cardiovascular response Cross-sectional, retrospective, prospective, and inter- (e.g., cardiac output) ventional epidemiologic research provide strong evidence 3. Larger muscle mass activation that regular physical activity reduces type 2 diabetes preva- Whether exercise training alters resting catecholamine lence in adolescents and adults with or without concomitant levels remains unclear. body composition changes.2,16,61,86,162 (Refer to http://www. acsm-msse.org/pt/pt-core/template-journal/msse/ Pancreatic Hormones media/0700.pdf for the ACSM position stand on physical activity and type 2 diabetes.) Those individuals at greatest Endurance training maintains blood levels of insulin and risk for type 2 diabetes (obese, hypertensive, family history, glucagon during physical activity closer to resting levels. In sedentary lifestyle) gain the greatest benefit from regular essence, the trained state requires less insulin at any stage physical activity.1,100,125 For adult men and women, low 97818_ch20.qxd 8/4/09 11:56 PM Page 435

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 435 fitness levels coincide with increased clustering of the metabolic abnormalities associated with the Metabolic Syndrome BMI≤25 (see p. 425), the “deadly quartet” of insulin resistance, BMI>25 1.2 glucose intolerance, upper-body obesity, and dyslipidemia. BMI strata For sedentary, middle-aged men, aerobic exercise plus weight 1.0 0.8 loss lowers blood pressure and improves glucose and fat me- Reference 0.6 tabolism.31,87 It may even reduce the amount of antidiabetic 0.4 medication a patient currently takes to control the disease.172

Relative risk 0.2 A 6-year clinical trial evaluated the effects of diet and physi- 0.0 cal activity lifestyle interventions on the occurrence of type 2 A 12345 diabetes in individuals with impaired glucose tolerance. Men and women were randomly assigned to either control, diet- Hypertension absent only, exercise-only, or diet-plus-exercise groups. Diet modifi- Hypertension present cation consisted of 25 to 30 kCal per kg of body mass (55 to 1.2 History of hypertension 60% carbohydrate, 25 to 30% lipid, and 10 to 15% protein) 1.0 for individuals with a BMI below 25. Those with a BMI 0.8 Reference above 25 maintained the same macronutrient mixture as the 0.6 leaner group while gradually losing weight at a rate of 0.5 to 0.4

1.0 kg per month until their BMI decreased to 23. Physical Relative risk 0.2 activity intervention required a progressive increase in the 0.0 B 12345 quantity of mild-to-moderate regular physical activity. The dietÐexercise intervention combined the major components of Diabetes absent both diet and exercise treatments. FIGURE 20.26 shows that diet, physical activity, and combined dietÐexercise interventions Diabetes present 1.2 decreased incidence of diabetes after the 6-year intervention. Parental history of diabetes A large prospective study evaluated diabetes risk for a 1.0 0.8 cohort of 70,102 female nurses aged 40 to 65 years without Reference diabetes, cardiovascular disease, or cancer at baseline meas- 0.6 urements in 1986.67 In agreement with previous prospective 0.4

research on men, an 8-year follow-up found increased physi- Relative risk 0.2 0.0 cal activity correlated with a substantially reduced relative C 1 2345 risk for type 2 diabetes. FIGURE 20.27 indicates that after ad- Quintiles of MET-hours for total physical activity justment for smoking, alcohol use, history of hypertension, and elevated cholesterol levels, relative risk across physical Figure 20.27 • Multivariate relative risks of type 2 diabetes according to MET-hours for total physical activity quintile (ascending 20-percentile units) within strata of (A) body mass index (BMI), (B) history of hypertension, and (C) parental 90 history of diabetes. MET-hours for total physical activity represents average time per week spent in each of eight physical activities multiplied by the MET value of each 70 activity. The MET value equals energy need per kilogram of Mean body mass per hour of activity divided by the energy need per kilogram of body mass per hour at rest. (From Hu GB, 50 et al. Walking compared with vigorous physical activity and the risk of type 2 diabetes in women: a prospective study. JAMA 1999;282:1433.) 30 at 6- y ear f ollow-up

Percent diabetes incidence Percent activity quintiles (20-percentile units) related inversely to dia- 10 Control Diet Exercise Diet + Exercise betes risk in lean and overweight women. The doseÐresponse relationship remained consistent in those at low or high risk for diabetes and stayed significant after BMI adjustment. Figure 20.26 • Effects of dietary and exercise lifestyle Women who walked regularly achieved greater benefits with interventions on the occurrence of type 2 diabetes in individuals with impaired glucose tolerance. (From Xiao-ren a brisker walking pace; the most vigorous exercise lowered P, et al. Effects of diet and exercise in preventing NIDDM in diabetes risk by 46%. Equivalent energy expenditures from people with impaired glucose tolerance. Diabetes Care walking or other forms of physical activity produced compa- 1997;20:537.) rable risk reduction. 97818_ch20.qxd 8/4/09 11:56 PM Page 436

436 Section 3 Aerobic Systems of Energy Delivery and Utilization Exercise Training

Skeletal Muscle Pancreas Adipose Tissue Liver

Insulin Quality of muscle Abdominal sensitivity Muscle Muscle mass Hyperinsulinemia adiposity blood flow ?

Capillary Fiber type Biochemical Glucose density IIb IIa changes storage area TNF-alpha Insulin receptor density GLUT-4

Glucose Muscle glucose Insulin receptors FFA release uptake delivery Insulin cascade GLUT4 Hexokinase Glucose disposal enzymes Glycogen synthase activity FFA Plasma FFA clearance

Gluconeogenesis

Muscle glucose extraction

Glucose uptake Hepatic glucose output

Control of Blood Glucose Figure 20.28 • Possible mechanisms of how regular physical activity improves insulin action and blood glucose homeostasis in type 2 diabetes. TNF-alpha, tumor necrosis factor-alpha, a hormonelike substance released from active adipocytes in the abdominal region, which may depress insulin-regulated glucose transport. (Modified from Ivy JL, et al. Prevention and treatment of noninsulin- dependent diabetes mellitus. Exerc Sport Sci Rev 1999;27:1.)

FIGURE 20.28 outlines the possible mechanisms of how Glycemic Control. Skeletal muscle consumes the major exercise training—via its effects on skeletal muscle, adipose amount of glucose transported in blood. Muscle, for example, tissue, liver, and pancreatic hormone output—improves in- generally clears between 70 and 90% of the glucose in an oral sulin action and blood glucose control in type 2 diabetes. or intravenous glucose challenge. A single bout of moderate or intense physical activity abruptly decreases plasma glucose Physical Activity Benefits for Type 2 Diabetes. levels, an effect that persists for up to several days. Extending Exercise training provides considerable benefits for persons the duration of weekly physical activity from 115 minutes with type 2 diabetes.59,129 to 170 minutes produces the greatest increase in insulin 97818_ch20.qxd 8/4/09 11:56 PM Page 437

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 437 sensitivity.66 Most likely, the immediate effects of each exer- Psychologic Profile. Improved exercise capacity in dia- cise session on increasing the active muscles’ insulin sensitiv- betic persons relates to decreased anxiety, improved mood ity causes long-term improvement in glycemic control, not and self-esteem, increased sense of well-being and psycho- any exercise-induced chronic adaptations in tissue function. logic control, enhanced socialization, and improved quality of 106 When resuming a sedentary lifestyle, the muscles’ sensitivity life. to insulin decreases, thus requiring more insulin to clear a given quantity of blood glucose.117 Improved insulin sensitiv- Occurrence of Type 2 Diabetes. Regular physical activity with regular physical activity provides type 2 diabetics ity contributes to delaying and even preventing the onset of with important “therapy” that ultimately lowers their insulin insulin resistance and type 2 diabetes in persons at high risk requirement. Three factors account for the improved insulin for developing this disease. Exercise benefits are particularly sensitivity for glucose transport in skeletal muscle and adi- pronounced for obese individuals and perhaps all persons pose tissue after a bout of physical activity: with increased abdominal fat deposition. 1. Translocation of the glucose transporter protein Exercise Risks for Type 2 Diabetes. FIGURE 20.29 lists GLUT-4 from the endoplasmic reticulum to the cell potential adverse effects of exercise in type 2 diabetics. One surface can minimize these risks by properly screening patients be- 2. Increase in total quantity of GLUT-4 fore they start an exercise program and carefully monitoring 3. Increase in glycogen synthase activity and subse- them during exercise when the program begins. quent glycogen storage (independent of any effect on 23,58,64,69,131 insulin signaling) Exercise Guidelines for Type 1 Diabetes. The clinical The hyperinsulinemic patient who requires the largest in- usefulness of regular exercise to improve glucose control in sulin release for glucose regulation derives the greatest benefits type 1 diabetes remains uncertain. To complicate matters for from regular physical activity.159 This observation supports the type 1 diabetics, physical activity can trigger a potentially theory that regular physical activity acts by reversing insulin re- dangerous dual response: (1) enhanced glucose uptake by sistance (i.e., physical activity increases insulin sensitivity). active muscles and (2) greater than anticipated exogenous in- Combining resistance exercise and endurance training im- sulin distributed by more rapid circulation that accompanies proves markers of insulin resistance and body composition for physical activity. These two factors could worsen the imbal- insulin-resistant individuals more than endurance training ance between glucose supply and use, increasing the risk of alone.87,158 Benefits of resistance plus endurance training for serious complications from hypoglycemia. “In a Practical hyperinsulinemia most likely come from the specific effects of Sense” on page 428 offers physical activity guidelines for the activating a relatively larger muscle mass (than with endur- diabetic patient, including those with well-controlled type 1 ance training alone) and additional caloric expenditure. diabetes who wish to perform prolonged and strenuous exer- Improvements in blood glucose homeostasis with regular physi- cise while minimizing the principal risk of hypoglycemia. cal activity rapidly decrease once training ceases and completely dissipate within several weeks of inactivity. Interestingly, recent research indicates that reliance on intensive pharmaco- RESISTANCE TRAINING AND logic therapy to lower blood glucose levels in high-risk type 2 ENDOCRINE FUNCTION diabetics increased mortality and did not significantly reduce 156 Muscle remodeling in resistance training reflects a complex cardiovascular events compared with standard therapy. process of cell receptor interaction with different hormones and DNA-mediated production of new contractile proteins. Cardiovascular Disease. Excess morbidity and mortal- The specific exercise response to muscular overload initially ity in type 2 diabetes results from coronary heart disease, links to configuration of the exercise stimulus—intensity, fre- stroke, and peripheral vascular disease from accelerated ath- quency, volume, sequence, mode, and recovery interval. erosclerosis. Disease risk factors that improve with regular FIGURE 20.30 proposes how resistance exercise training im- physical activity include hyperinsulinemia, hyperglycemia, proves overall muscular size, strength, and power. Hormonal abnormal plasma lipoproteins, some blood coagulation param- factors responsible for exercise-induced changes in muscle eters, and hypertension. size and function include the following:

Weight Loss. Weight loss and accompanying reduction 1. Changes in hepatic and extrahepatic hormone clear- in body fat and its distribution enhance glucose tolerance and ance rates insulin sensitivity.5,86 The beneficial effects of physical activ- 2. Differential rates of hormone secretion (and accom- ity on fat loss often are underestimated because body weight panying fluid shifts around the receptor sites) changes per se with exercise do not necessarily reflect the 3. Altered receptor-site activation via neurohumoral even more favorable, exercise-induced body composition control. In general, early-phase adaptations to resist- changes (fat loss and muscle gain). Combining diet and regu- ance training reflect a hormonal response that medi- lar physical activity reduces body fat in diabetic persons more ates neuromuscular system adaptations that improve effectively than either treatment alone. muscle strength 97818_ch20.qxd 8/4/09 11:56 PM Page 438

438 Section 3 Aerobic Systems of Energy Delivery and Utilization

System Potential Problem

•Retinal hemorrhage Systemic •Increased proteinuria •Acceleration of microvascular lesions •Cardiac arrhythmias Cardio- •Ischemic heart disease (often silent) vascular •Excessive blood pressure during exercise •Postexercise orthostatic hypertension

Metabolic •Increased hyperglycemia •Increased ketosis

•Foot ulcers (in presence of neuropathy) Musculo- •Orthopedic injury related to neuropathy skeletal •Accelerated degenerative joint disease

Figure 20.29 • Potential physical and physiologic problems and problem areas faced by type 2 diabetics who begin a physical activity program.

Testosterone and GH are two primary hormones that affect hormonal environment for muscular growth (hypertrophy). In adaptations to resistance training. Testosterone augments GH contrast, most studies fail to demonstrate changes in testos- release and interacts with nervous system function to increase terone and GH concentrations with training in females. Thus, muscle force production. These roles may be more important gender differences in hormone output with resistance training than any direct anabolic effect of testosterone per se. A single may ultimately explain variations in responsiveness of muscle session of resistance training generally elicits a short-term rise strength and size to prolonged muscular overload. in serum testosterone and decrease in cortisol, with a greater re- Testosterone response to resistance exercise reveals sev- sponse in men than women.29,49,83 Concurrently, catecholamine eral factors that increase its release. Most effective include in- release from the adrenal medulla increases with the acute stress tense activation of large-muscle groups with dead lifts, power of high-force and high-power exercise protocols.18 cleans, and squats, and other forms of heavy resistance exer- Resistance training in men increases frequency and ampli- cise (i.e., 85 to 95% 1-RM) or high-volume (total quantity) tude of testosterone and GH secretion, thereby creating a favorable training with multiple sets and/or physical activity with less

Heavy Hormonal Receptor resistance release Transport interactions exercise mechanisms

Cellular effects

Increased strength Increased force Cellular production and power adaptations capacity

Figure 20.30 • Schematic model of how heavy resistance training produces favorable adaptations in muscle structure and maximal strength performance. (Modified from Kraemer WJ. Endocrine responses and adaptations to strength training. In: Komi PV, ed. Strength and power in sport. London: Blackwell Scientific, 1992.) 97818_ch20.qxd 8/4/09 11:56 PM Page 439

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 439 than 1-minute rest intervals.84 Long-term resistance training 8 weeks of endurance training. Contrasting research showed in men increases resting testosterone levels, which correlates that general physical conditioning augmented -endorphin 20 with the pattern of strength improvement over time.56 and -lipotropin release in exercise. Greater endorphin release also occurs with sprint-type training, suggesting that 81 OPIOID PEPTIDES AND anaerobic factors also affect endorphin dynamics. Exercise training can increase an individual’s sensitivity PHYSICAL ACTIVITY to opioid effects, thus reducing the amount of hormone re- Scientists who studied the pain-relieving effects of opioid quired to induce a specific effect. Regular physical activity peptides (e.g., morphine) on brain function in the 1970s re- causes the opioids produced during physical activity to de- ported these substances exhibited neurotransmitter effects grade more slowly than in the pretraining condition.70 A and targeted specific opioid brain receptor sites. With this slower rate of hormone disposal facilitates and prolongs an finding came the realization that perhaps the brain itself pro- opioid response and possibly augments one’s tolerance for ex- duced endogenous opioid, mood-altering substances. Evidence tended physical activity. Taken in total, one could view the for existence of endogenous substances with opiate-like be- endogenous opioid response to regular physical activity as a havior first emerged with the isolation and purification of form of “positive addiction.” two opioid pentapeptides, methionine and leucine enkephalin (Greek, meaning “in the brain”). These opioids form part of a INTEGRATIVE QUESTION larger propiocortin precursor molecule produced in the anterior pituitary. Other opioid substances include -lipotropin, List four supplements at your local health food -endorphin, and dynorphin, (the most potent of the opioid store that claim to enhance exercise performance. peptides). Which supplements purport to stimulate hormone The various endogenous opioids exert widespread effects release? Based on hormonal regulation and with a range in function from neurohormones to neurotrans- function, explain whether these products can mitters. Endogenous opiates strongly inhibit hormonal release deliver on their claims. from the anterior pituitary, principally LH and FSH release. This inhibition may play a key role in menstrual cycle disturbances observed among many physically active women— PHYSICAL ACTIVITY, INFECTIOUS delay in menarche, dysfunctional uterine bleeding, secondary ILLNESS, CANCER, AND amenorrhea, and inadequacy of the luteal phase. In contrast to their inhibitory role, the opioid peptides stimulate GH and IMMUNE RESPONSE PRL release. “Don’t exercise when fatigued or you’ll get sick” reflects the Endorphins also regulate other hormones including common perception of parents, athletes, and coaches that ex- ACTH, the catecholamines, and cortisol. Serum concentra- cessive intense exercise increases susceptibility to certain ill- tions of -endorphin and/or -lipotropin generally increase nesses. In contrast, some also believe that regular, more with physical activity similarly in men and women, although moderate physical activity improves health and reduces sus- the response varies among individuals and varies inversely ceptibility to the common cold. with exercise intensity.35,48,81 Physical activity increases - Studies as early as 1918 reported that most cases of endorphin up to five times the resting level and probably even pneumonia in boys in boarding school occurred among ath- more in the brain itself,74 particularly region-specific effects letes, and respiratory infections seemed to progress toward in frontolimbic brain areas that are involved in the processing pneumonia after intense sports training. Anecdotal reports of affective states and mood.11 With resistance exercise, - also related the severity of poliomyelitis to participation in in- endorphin release varies with the exercise protocol; longer tense physical activity at the critical time of infection. Current duration (lighter resistance) and longer interset rest intervals epidemiologic and clinical findings from the field of exercise elicit the greatest response.82 immunology—the study of the interactions of physical, The precise physiologic significance of the response of environmental, and psychologic factors on immune func- the various endogenous opioid peptides to physical activity re- tion—support the contention that short-term, unusually stren- mains unclear, but several noteworthy effects emerge. These uous physical activity affects immune function to increase include the postulated opioid effect in triggering the exercise susceptibility to illness, particularly upper respiratory tract in- high, a state described as euphoria and exhilaration as the du- fection (URTI). Repeated URTI may signal a state of over- ration of moderate-to-intense aerobic exercise increases. training (see Chapter 21). Endorphin secretion also may increase pain tolerance, improve The immune system comprises a highly complex and appetite control, and reduce anxiety, tension, anger, and confu- self-regulating grouping of cells, hormones, and interactive sion. Interestingly, these effects generally reflect the docu- modulators that defend the body from invasion from outside mented psychologic benefits of regular physical activity. microbes (bacterial, viral, and fungal), foreign macromole- The effect of exercise training on endorphin response re- cules, and abnormal cancerous cell growth. This system has two mains controversial. One study reported no significant change functional divisions: (1) innate immunity and (2) acquired in -endorphin response to prolonged exercise following immunity. The innate immune system includes anatomic and 97818_ch20.qxd 8/4/09 11:56 PM Page 440

440 Section 3 Aerobic Systems of Energy Delivery and Utilization

Stress Exercise

Above average

Immune system

Average Illness Risk of URTI

Figure 20.31 • Theoretical model of the interrelationships between stress, physical activity, illness, and the immune system. (From MacKinnon LT. Current challenges and future Below expectations in exercise immunology: back to the future. average Med Sci Sports Exerc 1994;26:191.) Sedentary Moderate Very high Exercise volume and intensity physiologic components (skin, mucous membranes, body temperature, and specialized defenses such as natural killer cells, Figure 20.32 • General model showing the relationship diverse phagocytes, and inflammatory barriers). The acquired between intensity of physical activity and susceptibility to immune system consists of specialized B- and T-lymphocyte upper respiratory tract infection (URTI). Moderate exercise cells. When activated these cells regulate a highly effective reduces risk of URTI, whereas exhaustive competition or immune response to a specific infectious agent. If infection training places the participant at increased risk. (From does occur, an optimal immune system diminishes the severity Nieman DC. Exercise, upper respiratory tract infection, and of illness and speeds recovery. the immune system. Med Sci Sports Exerc 1994;26:128.) FIGURE 20.31 shows a proposed model for the interactions of physical activity, stress, illness, and the immune system. and increases risk of URTI that manifests itself within 1 to Within this framework, physical activity, stress, and illness 2 weeks,28,114 particularly for athletes prone to illness.25 interact, each exerting its separate effect on immunity. For ex- Approximately 13% of the participants in a Los Angeles ample, physical activity affects susceptibility to illness, while marathon reported an episode of infectious URTI during the certain illnesses clearly affect exercise capacity. Likewise, week following the race. For runners of comparable ability psychologic factors (via links between the hypothalamus and who did not compete for reasons other than illness, the infec- immune function) and other forms of stress, including nutrition rate approximated just 2%.115 tional deficiencies and acute alterations in normal sleep schedule, influence resistance to illness. Concurrently, physi- Short-Term Exercise Effects cal activity can either positively or negatively modulate the response to stress. Each factor—stress, illness, and short- and ¥ Moderate exercise: Moderate exercise boosts natu- long-term exercise—exerts an independent effect on immune ral immune functions and host defenses for up to sev- status, immune function, and resistance to disease. eral hours.45 Noteworthy effects include increases in natural killer (NK) cell activity. These phagocytic Upper Respiratory Tract Infections lymphocyte subpopulations enhance the blood’s cytotoxic capacity and provide the first line of defense FIGURE 20.32 describes the general J-shaped curve relating ex- against pathogens. The NK cell does not require prior ercise volume and/or intensity and susceptibility to URTI. or specific sensitization to foreign bodies or neoplas- Different immune function markers generally follow an in- tic cells. Rather, these cells demonstrate spontaneous verted J-shaped curve.123,174 Implications drawn from this re- cytolytic activity that ultimately ruptures and/or inac- lationship may be simplistic, but light to moderate physical tivates viruses and depresses the metastatic potential activity offers more protection against URTI and possibly di- of tumor cells. verse cancers than a sedentary life-style.96,99,141 Moderate ¥ Exhaustive exercise: Prolonged exhaustive exercise physical activity does not exacerbate the severity and duration (and other forms of extreme stress or increased train- of illness when an infection occurs.163 In contrast, a marathon ing) severely depresses the body’s first line of de- run or intense training session provides an “open window” fense against infection.80,93,112,126,165 Repeated cycles (3 to 72 h) that decreases antiviral and antibacterial resistance of unusually intense exercise and sports participation 97818_ch20.qxd 8/4/09 11:56 PM Page 441

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 441 further compound the risk. Impaired immune func- weight loss.38,40,146 Areas of improvement include enhanced tion from strenuous exercise “carries over” to a sec- functional capacity of natural cytotoxic immune mechanisms ond bout of exercise on the same day to augment (e.g., antitumor actions of NK cell activity) and diminished negative changes in neutrophils, lymphocytes, and age-related decrease in T-cell function and associated cy- 136 select CD cells. Elevated temperature, cytokines, tokine production.74 The cytotoxic T cells defend directly and various stress-related hormones (epinephrine, against viral and fungal infections and help regulate other im- GH, cortisol, -endorphins) in exhaustive exercise mune mechanisms. may mediate the transient depression of innate (NK If exercise training enhances immune function, one cell and neutrophil cytotoxicity) and depress adaptive might ask why trained individuals show increased susceptibil- 148,153 immune defenses (T- and B-cell function). ity to URTI after intense competition. The open window hy- Reduced immunity following strenuous exercise re- pothesis maintains that an inordinate increase in training or mains in the mucosal immune system of the upper competition exposes highly conditioned athletes to abnormal 47,109,160 respiratory tract. and associates with in- stress that transiently but severely depresses NK cell function. 113 creased URTI risk. This negative effect on immune This period of immunodepression (open window) decreases response clearly supports advising individuals with natural resistance to infection. The inhibitory effect of strenu- URTI symptoms to refrain from physical activity (or ous physical activity on ACTH and cortisol’s maintenance of at least “go easy”) to optimize normal immune mech- optimal blood glucose concentrations may negatively affect anisms that combat infection. TABLE 20.6 summarizes the immune process. For individuals who exercise regularly components of the immune system that exhibit tran- but only at moderate levels, the window of opportunity for sient changes after prolonged intense exertion. infection remains “closed,” thus maintaining the protective benefits of regular physical activity on immune function. Long-Term Exercise Effects Resistance Training. Nine years of prior resistance ex- Aerobic training positively affects natural immune func- ercise training did not affect resting NK cell activity or num- tions in young and old individuals and obese persons during ber compared to sedentary controls.116 Comparisons also indicated that resistance training activated monocytes more than typically observed for aerobic training. Monocyte activa- TABLE 20.6 • Immune System Components tion releases prostaglandins that downregulate NK cells fol- that Exhibit Negative Change lowing physical activity, thus blunting the long-term positive after Prolonged, Intense effect of physical activity on NK cells. These researchers had Exercise previously reported a 225% increase in NK cells following a short-term bout of resistance exercise,117 a response similar to ¥ High neutrophil and low lymphocyte blood counts, induced the short-term effect of moderate aerobic exercise.42 by high concentrations of plasma cortisol ¥ Increase in blood granulocyte and monocyte phagocytosis (engulfing of infectious agents and of breakdown products of Perhaps a Role for Nutritional Supplements. Nutrition muscle fiber); decrease in nasal neutrophil phagocytosis may optimize immune system function with strenuous exercise ¥ Decrease in granulocyte oxidative-burst activity (killing and training.46,62,101,138 activity) ¥ Decrease in nasal mucociliary clearance (sweeping movement Macronutrients. Consuming a high-fat diet (62% energy of cilia) ¥ Decrease in NK-cell cytotoxic activity (the ability to kill from lipids) negatively affected the immune system compared infected cells or cancer cells) to a carbohydrate-rich diet (65% energy from carbohydrates). ¥ Decrease in mitogen-induced lymphocyte proliferation (a In general, endurance athletes who ingest carbohydrate during measure of T-cell function) a race or prolonged trial experience lower disruption in hor- ¥ Decrease in the delayed-type hypersensitivity skin response monal and immune measures (indicating a diminished level of (the ability of the immune system to produce hard red lumps physiologic stress) than athletes not consuming carbohy- after the skin is pricked with antigens) 139 ¥ Increase in plasma concentrations of pro- and drate. Supplementing with a 6% carbohydrate beverage antiinflammatory cytokines (e.g., interleukin-6 and (0.7l L before; 0.25 L every 15 min during; 500 mL every h interleukin-1 receptor antagonist) throughout a 4.5-h recovery) depressed cytokine levels in the ¥ Decrease in ex vivo production of cytokines (interferon-8, inflammatory cascade after 2.5 hours of running at 77% interleukin-1, and interleukin-6) to mitogens and endotoxin 111 ¥ Decrease in nasal and salivary IgA concentration (an VO2max . Consuming carbohydrates (4 mL per kg of body important antibody) mass) every 15 minutes during 2.5 hours of high-intensity ¥ Blunted expression of major histocompatibility complex running or cycling maintained higher plasma glucose levels in (MHC) II in macrophages (an important step in recognition of 10 triathletes during exercise than a placebo.119 A blunted foreign agents by the immune system) cortisol response and diminished pro- and antiinflammatory cytokine responses accompanied the higher plasma glucose From Nieman DC. Immunity in athletes: current issues. Sports Sci Exchange, Gatorade Sports Science Institute 1998;11(2). levels with supplementation in both forms of exercise. Similar benefits from carbohydrate ingestion for cortisol and select 97818_ch20.qxd 8/4/09 11:56 PM Page 442

442 Section 3 Aerobic Systems of Energy Delivery and Utilization antiinflammatory cytokines occur following marathon compe- Marathoners who ingested a glutamine drink (5 g L-glut- tition, regardless of age or gender.120 This suggests a carbohy- amine in 330 mL mineral water) at the end of a race and then drate-induced reduction in overall physiologic stress in 2 hours later reported fewer URTI symptoms than unsupple- prolonged high-intensity exercise. In contrast, carbohydrate in- mented athletes.21 In subsequent studies by the same re- gestion during two hours of intense resistance training pro- searchers to determine a possible protective mechanism, duced no effect on immune changes compared to similar glutamine’s effect on postexercise infection risk did not relate training with placebo ingestion.121 to any change in blood lymphocyte distribution.22 Appearance of URTI in athletes during intense training does not fluctuate Micronutrients. Combined supplementation with with changes in plasma glutamine concentration. Preexercise antioxidant vitamins C and E produces more prominent glutamine supplementation does not affect the immune re- immunopotentiating effects (enhanced cytokine production) sponse following repeated bouts of intense exercise.89 in young, healthy adults than supplementation with either Glutamine supplements taken 0, 30, 60, and 90 minutes after a vitamin alone.71 Also, a 200-mg daily vitamin E supplement marathon race prevented the drop in glutamine concentrations enhanced several clinically relevant indices of T-cellÐmediated following the race but did not influence lymphokine-activated function in healthy elderly subjects.102 Long-term daily killer cell activity, proliferative responses, or exercise-induced supplementation with a physiologic dose of vitamins and changes in leukocyte subpopulations.134 Based on current evi- minerals or with 200 mg of vitamin E did not lower the incidence, we cannot recommend glutamine supplements to reli- dence and severity of acute respiratory tract infections in non- ably blunt immunosuppression from exhaustive exercise. institutionalized persons aged 60 and older. For individuals with infections, those receiving vitamin E had longer total A General Recommendation illness duration and restriction of activity.50 to Optimize Immunity Daily supplementation with vitamin C benefits individuals engaged in intense exercise, particularly those predis- A lifestyle that emphasizes regular physical activity, posed to frequent URTI.60,127 Runners who received a maintenance of a well-balanced diet, reducing stress to a 600-mg daily vitamin C supplement before and for 3 weeks minimum, and obtaining adequate sleep generally opti- following a 90-km ultramarathon competition experienced mizes immune function. For weight loss, we recommend a fewer symptoms of URTI—running nose, sneezing, sore gradual approach because more rapid weight loss with throat, coughing, fever—than runners given a placebo. accompanying severe caloric restriction suppresses im- Interestingly, infection risk inversely related to race perform- mune function.115 With prolonged intense exercise, ingest- ance; those with the fastest times suffered more symptoms. ing about 1 L hÐ1 of a typical carbohydrate-rich sports URTI also appeared most frequently in runners with strenu- drink lessens negative changes in immune function from ous training regimens. For these individuals, additional vita- the stress of physical activity and accompanying carbohy- min C and E and perhaps carbohydrate ingestion before, drate depletion. In general, endurance athletes who con- during, and after prolonged stressful exercise may boost im- sume carbohydrate during a race experience a lower mune mechanisms for combating this type of infection.118 disruption in hormonal and immune measures than athletes More than likely, other stressors—sleep deficit, mental who do not consume carbohydrate. stress, poor nutrition, or weight loss—magnify stress on the immune system from a single or repeated bout of exhaustive The Physical Activity–Cancer Connection physical activity. Epidemiologic studies generally demonstrate a protective as- Glutamine and the Immune Response. The nonessen- sociation between regular physical activity and risk of breast, tial amino acid glutamine plays an important role in normal colon, lung, and prostate cancers (see Chapter 31).94,103 Long- immune function. One protective aspect concerns glutamine’s term enhancement of other natural immune functions may role as an energy fuel for nucleotide synthesis by disease contribute to the cancer-protective effect of regular physical fighting cells, particularly lymphocytes and macrophages that activity in addition to its beneficial effect on NK cell activity. defend against infection.19,142 In humans, sepsis, injury, Upgraded defenses include augmented phagocytic capacity of burns, surgery, and endurance exercise lower plasma and the monocyteÐmacrophage lineage combined with more skeletal muscle glutamine levels. Lowered plasma glutamine robust cytotoxic and intracellular killing capacities (T-cell levels most likely occur because glutamine demand by the activity) that inhibit tumor growth and destroy cancer liver, kidneys, gut, and immune system exceeds its supply cells.173 Other potential effects of regular physical activity on from the diet and skeletal muscle. The lowered plasma gluta- aspects of cancer development include beneficial changes in mine concentration may contribute to the immunosuppression the body’s antioxidant functions; endocrine profiles; that accompanies extreme physical stress.10,63,145 Thus, gluta- prostaglandin metabolism; body composition; and, in the case mine supplementation might reduce susceptibility to URTI of colon cancer, a beneficial increase in intestinal transit time. following prolonged competition or a bout of exhaustive In Chapter 31, we review the role of physical activity in the training. prevention and treatment of different cancers. 97818_ch20.qxd 8/4/09 11:56 PM Page 443

CHAPTER 20 The Endocrine System: Organization and Acute and Chronic Responses to Exercise 443 Summary 12. Testes in the male produce testosterone and ovaries in the female produce the estrogens estradiol and 1. The endocrine system consists of a host organ, a progesterone. transmitted substance (hormone), and a target or re- 13. Moderate aerobic and resistance exercise increases ceptor organ. Hormones consist of steroids or amino testosterone in untrained males. For females, plasma acid (polypeptide) derivatives. testosterone and estrogen levels increase during 2. Hormones alter rates of cellular reactions by acting moderate physical activity. at specific receptor sites to enhance or inhibit en- 14. Insulin increases glucose transport into cells to control zyme function. blood glucose levels and carbohydrate metabolism. 3. The amount of hormone synthesized, the amount re- 15. Total lack of insulin or decreased sensitivity or in- leased or taken up by the target organ, and the re- creased resistance to this hormone produces dia- moval rate from the blood influence blood hormone betes mellitus. concentration. 16. The -cells of the pancreas secrete glucagon, an in- 4. Most hormones respond to peripheral stimulus on sulin antagonist that raises blood sugar levels. an as-needed basis; others release at regular inter- 17. Exercise training exerts differential effects on rest- vals. Some secretory cycles span several weeks; ing and exercise-induced hormone production and others pattern on a 24-hour cycle. release. Trained persons have elevated hormone re- 5. The anterior pituitary secretes at least six hormones: sponse during physical activity for ACTH and corti- PRL, the gonadotropic hormones FSH and LH, cor- sol, and depressed values for GH, PRL, FSH, LH, ticotropin, TSH, and GH. testosterone, ADH, thyroxine, catecholamines, and 6. GH promotes cell division and cellular prolifera- insulin. No training response occurs for aldosterone, tion. IGFs (or somatomedins) mediate many of renin, and angiotensin. GH’s effects. 18. Exercise-induced elevation of -endorphins and 7. TSH controls the amount of hormone secreted by other opioid-like hormones contributes to euphoria, the thyroid gland; ACTH regulates output of hor- increased pain tolerance, “exercise high,” and al- mones from the adrenal cortex; PRL affects repro- tered menstrual function. duction and development of secondary sex 19. Unusually intense physical activity increases sus- characteristics of females; FSH and LH stimulate ceptibility to URTI. Moderate physical activity up- the ovaries to secrete estrogen in females and the grades immune responses to protect against URTI. testes to secrete testosterone in males. 20. Regular exercise training positively affects natural 8. The posterior pituitary secretes ADH, which con- immune functions. An enhanced immune profile trols water excretion by the kidneys. It also secretes protects against URTI and various cancers. oxytocin, an important hormone in birthing and lactation. 9. PTH controls blood calcium balance. It increases References are available online at ionic (free) calcium levels by stimulating three tar- http://thepoint.lww.com/mkk7e. get organs: bone, kidneys, and the small intestine. 10. TSH stimulates metabolism of all cells and increases carbohydrate and fat breakdown in energy metabolism. On the Internet 11. The medulla of the adrenal gland secretes epineph- World Health Organization: Diabetes Programme rine and norepinephrine. The adrenal cortex se- www.who.int/diabetes cretes mineralocorticoids (regulate extracellular American Diabetes Association: Diabetes Risk Calculator sodium and potassium levels), glucocorticoids www.diabetes.org/risk-test.jsp (stimulate gluconeogenesis and serve as insulin an- National Diabetes Information Clearinghouse (NDIC) tagonists), and androgens (control male secondary http://www.diabetes.niddk.nih.gov/ sex characteristics). 97818_ch20.qxd 8/4/09 11:56 PM Page 444 97818_ch21.qxd 8/4/09 6:00 PM Page 445

PART TWO

Applied Exercise Physiology 97818_ch21.qxd 8/4/09 6:00 PM Page 446

SECTION 4 97818_ch21.qxd 8/4/09 6:00 PM Page 447

Enhancement of Energy Transfer Capacity

OVERVIEW Throughout this book, we emphasize that different physical activities, depending on duration and intensity, activate highly specific energy transfer systems. We acknowledge the difficulty in placing certain activities into one category. For example, as a person increases aerobic fitness, an activity previously classified as anaerobic may become aerobic. In many cases, all three energy- transfer systems—adenosine triphosphate–phosphocreatine (ATPÐPCr) system, lactic acid system, and aerobic system—operate predominantly at different times during exercise, but each remains functional throughout the activity. Their relative contributions to the energy continuum directly relate to the duration and intensity (power output) of a specific activity. Brief power activities for up to 6 seconds duration rely almost exclusively on “immediate” energy generated from the breakdown of stored intramuscular high-energy phosphates, ATP and PCr. Consequently, power athletes (e.g., sprinters, football players, shot putters, pole vaulters) must gear training toward improving this energy-transfer capacity, including the force-generating capacity of targeted muscles that power their sport. As all-out movement progresses to 60 seconds in duration and power output decreases, most of the energy for movement still arises through fast and slow anaerobic pathways. These metabolic reactions also involve the glycolytic short-term energy system with subsequent lactate accumulation. As exercise intensity diminishes and duration extends to 2 to 4 minutes, reliance on energy from the intramuscular phosphagens and anaerobic glycolysis decreases, and aerobic ATP production becomes increasingly more important. As prolonged exercise duration increases, aerobic metabolism generates more than 99% of the total energy requirement. Clearly, an efficient training program allocates a proportionate commitment to targeted training of specific energy and physiologic systems activated in the activity. The chapters in this section discuss anaerobic and aerobic conditioning (Chapter 21), including procedures for training muscles to become stronger (Chapter 22), with emphasis on principles, methods, and short-term responses and longer-term training adaptations. In the final chapter (Chapter 23), we explore the safety and efficacy of diverse chemical, nutritional, and physiologic aids to enhance exercise training and physical performance.

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Interview with Dr. Bengt Saltin

Education: Södertälje Gymnasium (1955); Medical School, Karolinska Institute, Stockholm (1956Ð62); thesis in physiology, Karolinksa Institute, Stockholm (1964) Current Affiliation: Director, Copenhagen Muscle Research Centre at Rigshospitalet and the University of Copenhagen; Adjunct Professor, August Krogh Institute, University of Copenhagen Honors and Awards: See Appendix E, available online at http://thepoint.lww.com/mkk7e. Research Focus: Exploration of integrative cardiovascular and metabolic response to physical exercise, including studies on skeletal muscle in humans by direct needle biopsy Memorable Publication: Saltin B, et al. Response to exercise after bed rest and after training: a longitudinal study of adaptive changes in oxygen transport and body composition. Circulation 1968;38(Suppl 7):79.

STATEMENT OF CONTRIBUTIONS: biopsy. This pioneering work has had a profound influ- ACSM Honor Award ence on our understanding of the anatomical, physiological, and biochemical behavior of skeletal muscle and its In recognition of his studies, which provide a better un- interactions with the cardiovascular system. His recent derstanding of maximal oxygen uptake in human subjects work has determined the maximal flow capacity in active under different physiological and pathophysiological con- skeletal muscle and shows that the limiting factor in ditions, particularly thermal stress and dehydration. maximal oxygen uptake is the pumping capacity of the Dr. Saltin’s classic study on exercise after bed rest and heart. after training was the scientific foundation for the current Dr. Saltin has provided training for many of the current early ambulation and exercise treatment of patients with leaders in exercise and sports science, and they have coronary heart disease and the understanding of decondi- greatly benefited from his unique ability to acquire new tioning that occurs in space travel. knowledge by studying at all levels of integration. In the late 1960s, Dr. Saltin began his seminal studies on skeletal muscle in humans, obtained by direct needle

What first inspired you to enter the exercise Christensen, who was the professor of physiology at the science field? What made you decide to Royal School of Gymnastics. The week after I met with pursue your advanced degree and/or line Professor Hohwü-Christensen in the summer of 1958, I of research? started to work with him on a project that evaluated energy demands in intermittent exercise. During the se- ➤ In January of 1958, I had my oral examination in mesters, I helped with teaching while at the same time physiology as part of my medical studies. The exam- continuing my medical studies. In the fall of 1961, I de- iner was Professor Ulf von Euler (later the 1970 Nobel cided to go for a doctoral thesis in physiology, which I Prize winner in physiology or medicine for discoveries defended in May 1964. concerning humoral transmitters in the nerve terminal and the mechanisms for their storage, release, and inactivation). At the end of the examination, I was asked Who were the most influential people in your whether I would be interested in staying on career, and why? as a student instructor. My answer was yes. As I had an interest in orienteering (a common sport in ➤ Two people played a very important role in my sci- Scandinavia), I wanted to be associated with exercise- entific career. I would like to acknowledge Professor related research. Professor Euler called Erik Hohwü- Erik Hohwü-Christensen and Professor Per-Olof 448 97818_ch21.qxd 8/4/09 6:00 PM Page 449

Åstrand. Professor Hohwü-Christensen had been a student of Johannes Lindhard, the first Docent of the equivalent of an endowed Chair in Anatomy, Physiology, and Theory of Gymnastics at the University of Copenhagen, and had also done cooperative research with 1920 Nobel Prize winner August Krogh. Professor Per-Olof Åstrand at the Karolinska Institute was the equivalent of my PhD dissertation research advisor. My projects were concerned with trying to better understand maximal oxygen uptake in human subjects and its determinants under different physiological and pathophysiological conditions, particularly thermal stress and dehydration. The knowledge and passion of these two pioneer scientists encouraged a younger generation of researchers-to- be to focus on human integrative physiology.

What has been the most interesting/enjoyable aspect of your involvement in science? What was the least interesting/enjoyable aspect? ➤ This is a difficult question to answer. I have been very fortunate to work with many scientists from all over the world. For example, in 1965, I spent 1 year in the Department of Medicine at the University of Texas in Dallas. Later, I worked for 5 months at the John B. Pierce Institute and Department of Physiology at Yale University in New Haven, Connecticut. In 1972, I spent 2 months in the Department of Medicine at the University of California, San Francisco, and then in 1976, I spent 3 months working with David Costill in The Human Performance Laboratory at Ball State University in Muncie, Indiana. I also spent 4 months at Cumberland College and the Department of Physiology at New South Wales University in scientists describe a phenomenon, but they do not try hard Sydney, Australia. For my interest in high-altitude physiology enough to penetrate the mechanisms and thereby contribute to and temperature regulation, I was fortunate to spend from 1 to the fundamental understanding of the phenomenon. 5 months between the years of 1960 and 1989 in laboratories in Northern Norway studying the physical profile and health What advice would you give to students who of Nomadic Lapps, and at the following locations studying express an interest in pursuing a career in exercise high-altitude physiology: Mt. Evans (Colorado), Mexico City, science research? the Andes and Himalayan mountains, and Kenya. I also had a wonderful experience studying the physiological responses to ➤ Become very focused and learn basic techniques. Today, exercise in racing camels in the Arabian desert. exercise science is to a large extent the study of acute and chronic adaptations. Thus, one route I would highlight is to identify the exercise stimulus and the intracellular signalling What is your most meaningful contribution to the of genes of importance for muscle adaptation. In an article in field of exercise science, and why is it so important? Scientific American (September 2000), we pointed out that ➤ To try to better understand, not only to describe, basic phe- Olympic athletes depend on how well their muscles adapt to nomena concerned with physiological responses to exercise the stress of high-intensity aerobic, anaerobic, and resistance under various environmental conditions. Exercise science training. However, recent research suggests that the ratio of was a key area in science in the latter part of the nineteenth fast- to slow-twitch muscle fibers depends on inherited char- century and in the first three decades of the twentieth century. acteristics. Unfortunately, future genetic technologies could There are many reasons for the lack of major contributions change even that as athletes experiment with methods to en- since then. One reason could be that the majority of exercise hance muscle performance. 449 97818_ch21.qxd 8/4/09 6:00 PM Page 450

450 Section 4 What interests have you pursued outside your professional career? ➤ I have been heavily involved in the sport of orienteering, both as a runner and administrator. From 1982 to 1988, I served as a Board Member and President of the International Orienteering Federation. I am a theater freak and have an interest in literature. Ibsen and Strindberg are my favorites, but most classical plays from antique Greece onwards will bring me to the theater. Throughout life my “reading compan- ions” have been Katherine Mansfield, Albert Camus, Joseph Brodsky, and, to name a Dane, J. P. Jacobsen.

You have the opportunity to give a last lecture. Describe its primary focus. ➤ I have given my “last” lecture. It focused on how young exercise physiologists could best serve an area in research and also make a major contribution to science. A major point was to identify an important phenomenon. If there are ample methods to study it, then stay with it until it has been solved. In other words, be mechanistic, carefully explain the phenom- ena, and then do whatever you can to understand it. 97818_ch21.qxd 8/4/09 6:00 PM Page 451

CHAPTER 21 Training for Anaerobic and Aerobic Power

CHAPTER OBJECTIVES

➤ Discuss and provide examples of the exercise ➤ Discuss the rationale for using heart rate to estab- training principles of (1) overload, (2) specificity, lish exercise intensity for aerobic training (3) individual differences, and (4) reversibility ➤ Discuss the term training-sensitive zone, including ➤ Outline the metabolic adaptations to anaerobic its rationale, advantages, limitations, and applica- exercise training tion for men and women of different ages ➤ Outline the metabolic, cardiovascular, and pul- ➤ Give the reason for adjusting the training-sensitive monary adaptations to aerobic exercise training zone for swimming and other forms of upper- ➤ body exercise Discuss factors that expand the a-v¯O2 difference during graded exercise, and how endurance ➤ Justify the “rating of perceived exertion” to estab- training affects each component lish exercise intensity for aerobic training ➤ Explain the effects of endurance training on ➤ Outline advantages of training at the lactate regional blood flow threshold ➤ Explain the term athlete’s heart; contrast structural ➤ Contrast continuous and intermittent aerobic and functional characteristics of the heart of an exercise training and advantages and endurance athlete versus a resistance-trained disadvantages of each athlete ➤ Summarize current recommendations by the ➤ Describe the influence of (1) initial fitness level, American College of Sports Medicine concerning (2) genetics, (3) training frequency, (4) training the quantity and quality of exercise to develop duration, and (5) training intensity on the aerobic and maintain cardiorespiratory and muscular training response fitness and joint flexibility in healthy adults

451 97818_ch21.qxd 8/4/09 6:00 PM Page 452

452 Section 4 Enhancement of Energy Transfer Capacity

➤ Outline the application of the overload principle ➤ Describe the most common form of overtraining to train the (1) intramuscular high-energy phos- syndrome and summarize interacting factors that phates and (2) glycolytic energy system contribute to overtraining in endurance athletes ➤ Summarize important factors about the exercise ➤ Summarize current recommendations for regular prescription for interval training physical activity during pregnancy

EXERCISE TRAINING PRINCIPLES competition. Application of these factors varies depending on performance and fitness goals. Several principles of physio- Stimulating structural and functional adaptations to improve logic conditioning are common to improving performance performance in specific physical tasks remains a major objec- in the diverse physical activity classifications illustrated in tive of exercise training. These adaptations require adherence FIGURE 21.1. The basic approach to physiologic conditioning to carefully planned programs, with focus on frequency and applies similarly to men and women within a broad age length of workouts, type of training, speed, intensity, duration, range; both respond and adapt to training in essentially the and repetition of the activity, rest intervals, and appropriate same way.

Exercise duration 0 s 4 s 10 s 1.5 min 3 min +

ATP Strength-power (power lift, high jump, javelin throw, golf swing, tennis serve)

ATP+PCr Sustained power (sprints, fast breaks, football line play, gymnastics routine)

ATP+PCr+Lactic Acid Anaerobic power-endurance

Types of performance Types (200-400m dash, 100m swim)

Electron Transport- Oxidative Phosphorylation Aerobic endurance (beyond 800m run)

Immediate/short-term Aerobic-oxidative system non-oxidative systems Predominant energy pathways

Figure 21.1 • Classification of physical activity based on duration of all-out exercise and the corresponding predominant intracellular energy pathways. 97818_ch21.qxd 8/4/09 6:00 PM Page 453

CHAPTER 21 Training for Anaerobic and Aerobic Power 453 Overload Principle effective evaluation of sport-specific performance occurs when the laboratory measurement most closely simulates the Regular application of a specific exercise overload enhances actual sport activity and/or uses the muscle mass and move- physiologic function to induce a training response. Exercising ment patterns required by the sport.12,57,111 Simply stated, spe- at intensities greater than normal stimulates highly specific cific exercise elicits specific adaptations to promote specific adaptations so the body functions more efficiently. Achieving training effects. Put another easy-to-remember way: speci- the appropriate overload requires manipulating training fre- ficity refers to Specific Adaptations to Imposed Demands quency, intensity, and duration, with focus on exercise mode. (SAID). The concept of individualized and progressive overload applies to athletes, sedentary persons, disabled persons, and even cardiac patients. An increasing number in this latter и Specificity of VO group have applied appropriate exercise rehabilitation to 2max walk, jog, and eventually run and compete in marathons and TABLE 21.1 presents evidence for the specificity of triathlons. As we discuss in Chapter 31, achieving health- endurance swim training on aerobic capacity improvements. related benefits of regular physical activity requires lower Fifteen men trainedи 1 hour daily, 3 days a week for 10 weeks. exercise intensity (but greater volume) than required to im- For all subjects, VO2max before and after training was meas- prove maximum aerobic fitness.107,126,203 ured during treadmill running and tethered swimming. Vigorous swimming elicits a general circulatory overload, so Specificity Principle the researchers expected at least minimal improvement (or “transfer”) in aerobic power from swimming to running. This Exercise training specificity refers to adaptations in meta- didи not occur. Almost total specificity accompanied the bolic and physiologic functions that depend upon the type and VO2max improvement with swim training. Use of treadmill mode of overload imposed. A specific anaerobic exercise running alone to assess swim training effects would have mis- stress (e.g., strengthÐpower training) induces specific strengthÐ takenly concluded no swim training effect! power adaptations; specific endurance exercise stress elicits When training for specific aerobic activities such as specific aerobic system adaptations—with only a limited cycling, swimming, rowing, or running, the overload must (1) interchange of benefits between strengthÐpower training engage the appropriate muscles required by the activity and and aerobic training. Nonetheless, the specificity principle (2) provide exercise at a level sufficient to stress the cardio- extends beyond this broad demarcation. Aerobic training, for vascular system. Little improvement occurs when measuring example, does not represent a singular entity that requires aerobic capacity with dissimilar exercise; the greatest im- only cardiovascular overload. Aerobic training that relies on provement occurs when the test exercise duplicates the specific muscles in the desired performance most effectively training exercise. These results also apply in exercise rehabil- improves aerobic fitness for swimming,57 bicycling,150 run- itation of patients with coronary artery disease.145 The data in 129 112 и ning, or upper-body exercise. Some evidence even sug- Table 21.1 also indicate that while swimming VO2max im- gests a temporal specificity in training response such that proved 11% with swim training, maximum exerciseи time indicators of training improvement peak when measured at increased 34% during the swim test. Improvements in VO2max the time of day when training regularly occurred.81 The most probably reach a peak during training. Thereafter, other

· TABLE 21.1 • Effects of 10 Weeks of Interval Swim Training on Changes in VO2max and Endurance Performance During Running and Swimming Subjects Measure Running Test Swimming Test

Swim Training Pretraining Posttraining % Change Pretraining Posttraining % Change ú VO2max L и minϪ1 4.05 4.11 1.5 3.44 3.82 11.0 mL и kgϪ1 и minϪ1 54.9 55.7 1.5 46.6 51.8 11.0 Max work time min 19.6 20.5 4.6 11.9 15.9 34.0 Nontraining Controls ú VO2max L и minϪ1 4.12 4.18 1.5 3.51 3.40 Ϫ3.1 mL и kgϪ1 и minϪ1 55.1 55.5 0.7 46.8 45.0 Ϫ3.8 Max work time min 20.7 19.7 Ϫ4.8 11.5 11.5 0

From Magel JR, et al. Specificity of swim training on maximum oxygen uptake. J Appl Physiol 1975;38:151. 97818_ch21.qxd 8/4/09 6:00 PM Page 454

454 Section 4 Enhancement of Energy Transfer Capacity

FOCUS ON RESEARCH Highly Specific Nature of the Training Response

Saltin B, et al. The nature of the training response: ¥ Training induced no change in muscle fiber com- peripheral and central adaptations to one-legged position but produced pronounced metabolic adap- exercise. Acta Physiol Scand 1976;96:289. tations reflected by enhanced SDH activity of the S- and E-trained legs, with no change in the NT ➤ In 1976, Saltin and colleagues performed one of the first leg.и These changes generally paralleled increases studies to document that regular exercise induces marked in VO2max. local adaptations in trained muscle. Importantly, these ad- ¥ Glycogen use during two-legged exercise justments enhance local blood flow and metabolism in re- remained lowest in the trained leg. Moreover, only sponse to physical activity and also contribute to general the untrained leg continuously released lactate cardiovascular function during exercise. during submaximal exercise. An elegant series of experiments separated local and 1. One-legged exercise general training effects. They applied different combina- и Figure 1 shows that VO increased nearly 20% tions of one-legged bicycle exercise to study simultaneously 2max with training in the E-trained leg, 11% in the adaptations of skeletal muscles and central circulatory func- S-trained leg, and 8% when exercising both legs tions with training. Healthy but otherwise sedentary males и Ϫ Ϫ (group A). S training of one leg only (group B) with pretraining VO of 46 mL и kg 1 и min 1 (range: и и 2max increased VO by 15%, whereas VO of the 37Ð54) were placed into three training groups: group A— 2max 2max nontrained leg increased less than 2%. One- one-legged endurance training (E) and the other leg sprint legged endurance training for group C increased training (S); group B—one-legged S and the other leg no и и VO by 24% in the trained leg while VO training (NT); group C—one-legged E and the other leg NT. 2max 2max with the NT leg increased just 6%. These results Exercise training performed on a bicycle ergometer with confirmed that training only one leg exerts little intensity adjusted to heart rate lasted 4 weeks, with an aver- effect on the nontrained leg, thus indicating con- age of 5 workouts per leg each week. The exercise intensity siderable training specificity. throughout training represented 75% for E and 150% for S и 2. Two-legged exercise of the one-legged VO assessed pretraining and at week 3 2max Analysis of pre- and posttraining two-legged to ensure proper training progression. Intensity and duration и VO revealed mean increases for groups A (9%), of each type of training produced similar total work output 2max B (10%), and C (8%). Figure 2 shows similar leg for each training bout. Total weekly energy output averaged blood flow (left panel) in trained and untrained 12,558 kCal per trained leg, with all groups achieving within legs and in E-trained legs compared with S-trained 5 to 10% of this value; group A, however, performed 90 _ legs. In addition, similarity existed for a-vO differ- to 95% more work than group B because their training 2 ence (middle panel) for S- and E-trained legs dur- required both legs. ing exercise. In the four subjects with one trained Pre- and posttraining measurements included needle _ and one untrained leg, the slightly higher a-vO dif- biopsy samples from the quadriceps femoris for histo- 2 ferences in the trained leg resulted from a lower chemical identification of muscle fiber type and area, oxygen content in the femoral blood draining the glycogen concentration, and succinate dehydrogenase trained leg (greater O extraction). Endurance- and (SDH) and ATPase activity. Subjects performed submaxi- 2 sprint-trained legs showed similar calculated oxy- mal and maximal exercise for each leg and during two- gen consumptions during exercise (right panel); legged maximal cycling (8 of 13 subjects provided data to some subjects, however, showed higher values in evaluate local metabolic adaptations to training). Measures the trained leg than in the untrained leg. included oxygen consumption, heart rate, arteriovenous _ oxygen difference (a-vO2 diff) in muscle blood flow The study’s major impact was demonstrating that an (catheters inserted in the two femoral arteries and veins to exercise training regimen elicits a distinct pattern of local measure each leg’s blood flow), and glucose and lactate. adaptations only in the trained muscles. These specific The three major findings were: local changes provide essential stimulation for the central и cardiovascular response to exercise. Saltin and coworkers ¥ Exercise training improved VO (particularly 2max concluded that peripheral adaptations to training probably for the E-trained leg) and lowered heart rate and contribute as much to the training response as the well- blood lactate in submaximal exercise only when documented improvement in central circulatory function. exercising with a trained leg.

Continued on page 455 97818_ch21.qxd 8/4/09 6:00 PM Page 455

CHAPTER 21 Training for Anaerobic and Aerobic Power 455

FOCUS ON RESEARCH Continued

Figure 1 • Mean percentage changes in

V˙ O2max in groups A, B, and C during one- legged exercise. Pretraining V˙ O2max values Ϫ (L и min 1) are indicated below each bar. The four bars on the far right indicate average values for all untrained, sprint- or endurance-trained limbs and values for two-legged exercise regardless of training group.

Leg blood flow Leg a-vO2 difference Oxygen consumption 7.0 20 7.0 18

) 6.0 ) 6.0

–1 17 –1 5.0 5.0 min min . 16 . 4.0 4.0 15 ) (Vol %) (T) ( S ) (Vol ) (L (T) ( S ) (L (T) ( S ) (L 0.5 14 0.5

0 0 0 0.50 4.0 5.0 6.0 7.0 0 14 15 16 17 18 20 0.50 4.0 5.0 6.0 7.0 (NT) (E) (L . min–1) (NT) (E) (Vol %) (NT) (E) (L . min–1)

Rest Untrained (NT)-Trained (T) Endurance trained (E)-Sprint trained (S)

Figure 2 • Leg blood flow (left panel), leg a-vO2 difference (middle panel), and oxygen consumption (right panel) in each leg for subjects performing two-legged exercise for 1 hour at 70% V˙ O2max. Comparisons are between the legs of four untrained subjects (NT) and four trained subjects (endurance-trained [T] or sprint- trained [S]). The panels also show trained and untrained leg comparisons for the four subjects who trained one leg with the endurance regimen and the other leg with sprint training.

mechanisms (only partly related to oxygen transport system Whereasи aerobic exercise training induces a highly capacity) support performance improvements. These adapta- specific VO2max improvement, more general improvements tions most likely take place within the active musculature take place in cardiac function. Ventricular contractility, for rather than the central circulatory system (see “Focus on example, that improves with one mode of exercise training Research,” p. 454). also improves when exercising the untrained limbs.205 97818_ch21.qxd 8/4/09 6:00 PM Page 456

456 Section 4 Enhancement of Energy Transfer Capacity Individuals apparently can train the myocardium per se with aerobic improvement also may result from greater regional diverse “big-muscle” exercise modes. blood flow in active tissues from (1) increased microcircula- tion, (2) more effective redistribution of cardiac output, or (3) the combined effect of both factors. Regardless of the mecha- Specificity of Local Changes nism, these adaptations occur only in specifically trained Overloading specific muscle groups with endurance muscles and only become apparent in exercise that activates training enhances exercise performance and aerobic power by this musculature. facilitating oxygen transport and oxygen use at the local level 82,122 of the trained muscles. For example, the vastus lateralis Individual Differences Principle muscle of well-trained cyclists has greater oxidative capacity than that of endurance runners; oxidative capacity in this All individuals do not respond similarly to a given training muscle improves considerably following training on a bicycle stimulus. For example, a person’s relative fitness level at the ergometer. Such local metabolic adaptations increase the start of training exerts an influence. This subprinciple of capacity of trained muscles to generate ATP aerobically initial values reveals that individuals with lower fitness before the onset of lactate accumulation. The specificity of deliver the greatest training improvement. This principle operates

TABLE 21.2 • Changes in Measures of Physiologic and Metabolic Function with Various Durations of Detraininga Change, % Change, % Short-Term Longer-Term Variable Trained Detrained Detrainingb Detrainingc ú и Ϫ1и Ϫ1 Ϫ VO2max, mL kg min 62.2 57.3 8 62.1 50.8 Ϫ18 ú и Ϫ1 Ϫ VO2max, L min 4.45 4.16 7 Cardiac output, L и minϪ1 27.8 25.5 Ϫ8 27.8 25.2 Ϫ10 Stroke volume, mL 155 139 Ϫ10 148 129 Ϫ13 Heart rate, b и minϪ1 186 193 4 187 197 5 Oxygen pulse, mL и bϪ1 12.7 10.9 Ϫ14 Sum 3-min recovery HR 190 237 25 Plasma volume, L 2.91 2.56 Ϫ12 _ и Ϫ1 Ϫ a-vO2 diff, mL 100 mL 15.1 15.4 2 (NS) 15.1 14.1 Ϫ7 PCr, mM и (g wet wt)Ϫ1 17.9 13.0 Ϫ27 ATP, mM и (g wet wt)Ϫ1 5.97 5.08 Ϫ15 Glycogen, mM и (g wet wt)Ϫ1 113.9 57.4 Ϫ50 Capillary density, cap и mmϪ2 511 476 Ϫ7 464 476 Ϫ2 (NS) Oxidative enzyme capacity Ϫ29 Ϫ32 Myoglobin, mg (g protein)Ϫ1 43.3 41.0 Ϫ5 (NS) 43.3 40.7 Ϫ6 Insulin (rest) 17Ð120 Norepinephrine/epinephrine (rest) No change Norepinephrine/epinephrine (exercise) 65Ð100 Blood lactate 88 Lactate threshold Ϫ7 Ϫ18 Exercise lipolysis Ϫ52 Muscle glycogen synthesis Ϫ29 Ϫ40 Time to fatigue, min Ϫ10 Swim power, W Ϫ14 Elbow extension strength, ft-lb 39.0 25.5 Ϫ35

aData represent an average computed from individual studies as cited in the following sources: McArdle WD, et al. Essentials of exercise physiology. 3rd ed. Lippincott Williams & Wilkins, 2006, and Wilber RL, Moffatt RJ. Physiological and biochemical consequences of detraining in aerobically trained individuals. J Strength Cond Res 1994;8:110. Note that a change for heart rate represents a decline in functional capacity. Omitted values for trained and detrained excluded in original sources. bShort term, 3 weeks or less in primarily aerobically trained individuals. cLonger term, 3 to 12 weeks in primarily aerobically trained individuals. NS, not statistically significant. 97818_ch21.qxd 8/4/09 6:00 PM Page 457

CHAPTER 21 Training for Anaerobic and Aerobic Power 457 for healthy individuals as well as those with cardiovascular research group confined five subjects to bed for 20 consecu- 18,166,224 180 и disease or at high risk for the disease. When a relative days. VO2max decreased by 25%. This decrease accom- tively homogenous group begins a regimen of exercise train- panied a similar decrement in maximal stroke volume and ing, one cannot expect each person to achieve the same state cardiac output, which decreased maximal aerobic power an of fitness (or exercise performance) after 10 or 12 weeks. A average of 1% per day. Additionally, the number of capillaries coach should not insist that all athletes on the same team (or within trained muscle decreased between 14 and 25% within even in the same event) train the same way or at the same rel- 3 weeks immediately following training.179 For elderly sub- ative or absolute exercise intensity. Optimal training benefits jects, 4 months of detraining completely negated endurance occur when exercise programs focus on individual needs and training adaptations on cardiovascular functions and body capacities of participants. Chapter 11 and page 476 of this water distribution.155 chapter emphasize that genetic factors interact to impact the Even among highly trained athletes, the beneficial training response. effects of many years of prior exercise training remain transient and reversible. For this reason, most athletes begin a recondi- tioning program several months prior to the start of the com- Reversibility Principle petitive season or, at a minimum, maintain some moderate Loss of physiologic and performance adaptations (detrain- level of off-season, sport-specific training to slow the decline ing) occurs rapidly when a person terminates participation in in physiologic functions from detraining. regular physical activity. Only 1 or 2 weeks of detraining reduces both metabolic and exercise capacity, with many 140 PHYSIOLOGIC CONSEQUENCES training improvements fully lost within several months. OF EXERCISE TRAINING TABLE 21.2 shows the biologic consequences of various durations of short-term (Ͻ3 weeks) and longer-term (3Ð12 The following sections present a more detailed listing of the weeks) detraining in endurance-trained individuals. The data diverse adaptations to the anaerobic and aerobic exercise represent average responses reported in the literature. One training responses outlined in TABLE 21.3.

TABLE 21.3 • Typical Metabolic and Physiologic Values for Healthy, Endurance-Trained and Untrained Mena Percentage Variable Untrained Trained Differenceb

Glycogen, mM и (g wet muscle)Ϫ1 85.0 120 41 Number of mitochondria, mmol3 0.59 1.20 103 Mitochondrial volume, % muscle cell 2.15 8.00 272 Resting ATP, mM и (g wet muscle)Ϫ1 3.0 6.0 100 Resting PCr, mM и (g wet muscle)Ϫ1 11.0 18.0 64 Resting creatine, mM и (g wet muscle)Ϫ1 10.7 14.5 35 Glycolytic enzymes Phosphofructokinase, mM и (g wet muscle)Ϫ1 50.0 50.0 0 Phosphorylase, mM и (g wet muscle)Ϫ1 4Ð6 6Ð9 60 Aerobic enzymes Succinate dehydrogenase, mM и (kg wet muscle)Ϫ1 5Ð10 15Ð20 133 Max lactate, mM и (kg wet muscle)Ϫ1 110 150 36 Muscle fibers Fast twitch, % 50 20Ð30 Ϫ50 Slow twitch, % 50 60 20 Max stroke volume, mL 120 180 50 Max cardiac output, L и minϪ1 20 30Ð40 75 Resting heart rate, b и minϪ1 70 40 Ϫ43 Max heart rate, bminϪ1 190 180 Ϫ5 _ и Ϫ1 Max a-vO2 diff, mL dL 14.5 16.0 10 ú и Ϫ1 и Ϫ1 VO2max, mL kg min 30Ð40 65Ð80 107 Heart volume, L 7.5 9.5 27 Blood volume, L 4.7 6.0 28 ú и Ϫ1 VEmax, L min 110 190 73 Percentage body fat 15 11 Ϫ27

aIn some cases, approximate values are used. In all cases, the trained values represent data from endurance athletes. Caution is advised in assuming that the percentage differences between trained and untrained necessarily results from training because genetic factors exert a strong influence on many of these factors. bPercentage by which the value for the trained differs from the corresponding value for the untrained. 97818_ch21.qxd 8/4/09 6:00 PM Page 458

458 Section 4 Enhancement of Energy Transfer Capacity

TABLE 21.4 • Changes in Resting Concentrations of PCr, Creatine, ATP, and Glycogen Following 5 months of Heavy- Resistance Training in 9 Male Subjects Percentage Variablea Control Posttraining differenceb

PCr 17.07 17.94 ϩ5.1 Creatine 10.74 14.52 ϩ35.2 ATP 5.07 5.97 ϩ17.8 Glycogen 86.28 113.90 ϩ32.0

From MacDougall JD, et al. Biochemical adaptation of human skeletal muscle to heavy resistance training and immobilization. J Appl Physiol 1977;43:700. aAll values are averages expressed in mM per gram of wet muscle. bAll percentage differences are statistically significant.

ANAEROBIC SYSTEM CHANGES training (TABLE 21.4) show increases in the trained WITH TRAINING muscle’s resting levels of ATP, PCr, free creatine, and glycogen, accompanied by a 28% improvement FIGURE 21.2 summarizes generalized responses for metabolic in muscular strength. Other studies have shown adaptations in anaerobic function that accompany anaerobic higher levels of ATP and total creatine content in training. Consistent with the concept of training specificity, ac- trained muscles of sprint runners and track speed tivities that demand a high level of anaerobic metabolism in- cyclists compared to distance runners and road rac- duce specific changes in the immediate and short-term energy ers.144 SpeedÐpower training also increases PCr systems without concomitant increases in aerobic functions. content of the trained skeletal muscle. Three important changes occur with anaerobic power training: 2. Increased quantity and activity of key enzymes that 1. Increased levels of anaerobic substrates. Muscle control the anaerobic (glycolytic) phase of glucose biopsy specimens taken before and after resistance catabolism. These changes do not achieve the magnitude observed for oxidative enzymes with aerobic training. The most dramatic increases in anaerobic enzyme function and fiber size occur in fast-twitch 100 muscle fibers. 90 3. Increased capacity to generate high levels of blood lactate during all-out exercise. This adaptation prob- 80 ably results from (1) increased levels of glycogen and glycolytic enzymes and (2) improved motivation 70 and tolerance to “pain” in fatiguing physical activity. 60 Research has not yet demonstrated that exercise training augments buffering capacity mechanisms. 50 g e increase Motivational factors probably improve training- 40 induced tolerance to elevated plasma acidity.

30 Percenta AEROBIC SYSTEM CHANGES 20 WITH TRAINING 10 FIGURE 21.3 shows the diverse physiologic and metabolic fac- 0 tors related to oxygen transport and use. With adequate training stimulus, the positive adaptations in many of these factors remain independent of race, gender, age and, in some instances, health status.25,31,186,223 Anaerobic enzymes PCr ATP Glycolytic capacity Glycogen content Metabolic Adaptations Figure 21.2 • Generalized potential for increases in anaerobic energy metabolism of skeletal muscle with short- Aerobic training improves the capacity for respiratory control term sprint–power training. in skeletal muscle. 97818_ch21.qxd 8/4/09 6:00 PM Page 459

CHAPTER 21 Training for Anaerobic and Aerobic Power 459

Ventilation-Aeration Central Blood Flow

• Minute ventilation • Cardiac output • Ventilation:perfusion ratio (heart rate, stroke volume) • Oxygen diffusion capacity • Arterial blood pressure • Hb—O2 affinity • Oxygen transport • Arterial oxygen saturation capacity [Hb]

Active Muscle Metabolism Peripheral Blood Flow

• Enzymes and oxidative • Flow to nonactive regions potential • Arterial vascular reactivity • Energy stores and substrate • Muscle blood flow availability • Muscle capillary density • Myoglobin concentration • O2 diffusion • Mitochondria size and • Muscle vascular conductance number • O extraction • Active muscle mass 2 • Hb—O affinity • Muscle fiber type 2 • Venous compliance and reactivity

Figure 21.3 • Physiologic factors that limit V˙ O2max and aerobic exercise performance. Hb, hemoglobin.

Metabolic Machinery of aerobic capacity during prolonged exercise without blood lactate accumulation. To some extent, mitochondrial potential and not oxygen supply limits the oxidative capacity of untrained muscle.72 Fat Metabolism. Endurance training increases the oxi- Endurance-trained skeletal muscle fibers contain larger and dation of fatty acids for energy during rest148 and submaximal more numerous mitochondria than less active fibers. The en- 49,85,214 exercise (FIG. 21.4). Enhanced fat catabolism becomes larged mitochondrial structural machinery and enzyme activity particularly apparent at the same absolute submaximal exer- adaptations with aerobic training (up to 50% increase in just a cise workload without regard to fuel input (fed or fasted),9,11,30 few weeks) greatly increase the capacity of subsarcolemmal and the effect occurs within two weeks of training.201 and intermyofibrillar muscle mitochondria to generate ATPaer- Impressive increases also occur in trained muscle’s capacity obically.65,84,198 A nearly twofold increase in aerobic system en- to use intramuscular triacylglycerols as the primary source for zymes within 5 to 10 days of training coincides with increased fatty acid oxidation.127 Four factors contribute to a heightened mitochondrial capacity to generate ATP aerobically. training-induced increased lipolysis: Increases in total mitochondrial material, not increased enzymatic activity per unit of mitochondrial protein, account 1. Greater blood flow within trained muscle for the enzyme changes. The increase in mitochondrial pro- 2. More fat-mobilizing and fat-metabolizing enzymes 3. Enhanced muscle mitochondrial respiratory capacity teinи by a factor of two exceeds the typical 10 to 20% increases in VO2max with endurance training. More than likely, enzy- 4. Decreased catecholamine release for the same matic changes allow a person to sustain a higher percentage absolute power output 97818_ch21.qxd 8/4/09 6:00 PM Page 460

460 Section 4 Enhancement of Energy Transfer Capacity combustion in submaximal exercise with endurance training results from the combined effects of the following: 1000 al) 1. Decreased muscle glycogen use 800 2. Reduced glucose production (decreased hepatic 600 glycogenolysis and gluconeogenesis) 400 3. Reduced use of plasma-borne glucose30

Ener gy f rom 200 Training-enhanced hepatic gluconeogenic capacity pro-

drate (k C carbo hy drate 0 vides further resistance to hypoglycemia during prolonged exercise.32,41 1000 800

al) Muscle Fiber Type and Size 600 400 Aerobic training elicits metabolic adaptations in each

f at (k C muscle fiber type. The basic fiber type probably does not

Ener gy f rom 200 “change” to any great extent; rather, all fibers maximize their 0 already existing aerobic potential. Selective hypertrophy occurs in the different muscle 1200 fiber types with specific overload training. Highly trained en- 1000 durance athletes have larger slow-twitch fibers than fast- gy 800 twitch fibers in the same muscle. Conversely, the fast-twitch 600 fibers of athletes trained in anaerobic power activities occupy

(k C al) a greater portion of the muscle’s cross-sectional area. 400 Total ener Total 200 Myoglobin. As might be expected, slow-twitch muscle 0 fibers with high capacity to generate ATP aerobically contain 0 30 60 90 120 relatively large quantities of myoglobin. Among animals, a Exercise duration (min) muscle’s myoglobin content relates to their level of physical activity. The leg muscles of hunting dogs, for example, con- Before training After training tain more myoglobin than the muscles of sedentary house pets; similar findings exist for grazing cattle compared with Figure 21.4 • Aerobic exercise training enhances fat penned animals.222 The effect of regular physical activity on catabolism in submaximal exercise. During constant-load, myoglobin levels in humans remains undetermined, but any prolonged exercise, total energy derived from fat oxidation effect is likely negligible. increases considerably following training. The carbohydrate- sparing adaptation results from facilitated release of fatty acids from adipose tissue depots (augmented by a reduced Cardiovascular Adaptations blood lactate level) and an increased amount of triacylglycerol within the endurance-trained muscle fibers. FIGURE 21.5 summarizes important adaptations in cardiovascu- (From Hurley BF, et al. Muscle triglyceride utilization during lar function with aerobic exercise training that increase oxy- exercise: effect of training. J Appl Physiol 1986;60:562.) gen delivery to active muscle.

Cardiac Hypertrophy: The “Athlete’s Heart” Enhanced fat catabolism in submaximal exercise benefits endurance athletes because it conserves the glycogen stores so Long-term aerobic training generally increases the important during prolonged, intense exercise. Improved fatty heart’s mass and volume with greater left-ventricular end- acid ␤-oxidation and respiratory ATP production contribute to diastolic volumes during rest and exercise. Moderate cardiac a cell’s integrity and high level of function. This enhances hypertrophy secondary to longitudinal myocardial cell en- endurance capacity independent of increases in glycogen largement reflects a fundamental and normal training adapta- reserves or aerobic power. tion of muscle to an increased workload independent of age.137 This enlargement is characterized by an increased size Carbohydrate Metabolism. Trained muscle exhibits of the left ventricular cavity (eccentric hypertrophy) and enhanced capacity to oxidize carbohydrate during maximal modest thickening of its walls (concentric hypertrophy). exercise. Consequently, large quantities of pyruvate flow Exercise training alters the contractile properties of car- through aerobic energy pathways in this type of exercise, an diac muscle fibers that include increased sensitivity to activa- ϩ effect consistent with increased mitochondrial oxidative tion by Ca2 , changes in forceÐlength relationship, and capacity and enhanced glycogen storage within muscles. increased power output.38 Myocardial overload stimulates Reduced carbohydrate as fuel and increased fatty acid greater cellular protein synthesis with concomitant reductions 97818_ch21.qxd 8/4/09 6:00 PM Page 461

CHAPTER 21 Training for Anaerobic and Aerobic Power 461

Ventricular compliance Internal ventricular Plasma dimensions volume Tot al Venous End diastolic blood return volume Red volume Maximum Maximum blood Myocardial Ejection stroke cardiac cell mass contractility fraction volume output

Effectiveness of cardiac output distribution

Optimization of peripheral flow

Blood flow to active muscle

O2 O2

O2 O O2 2

O2 O2 O2

Figure 21.5 • Adaptations in cardiovascular function with aerobic exercise training that increase oxygen delivery to active muscles.

in protein breakdown. Increasing trained muscle’s RNA waves to “map” myocardial dimensions and heart chamber content accelerates protein synthesis. Individual myofibrils volume (see Chapter 32). This technique has evaluated the thicken, while the number of contractile filaments increases. structural characteristics of hearts of male and female athletes The heart volume of sedentary men averages about (and other species of mammals) to determine how various 800 mL. In athletes, increases in heart volume relate to the modes of exercise training differentially affect cardiac aerobic nature of the sport—endurance athletes average a enlargement.151,199 25% larger heart volume than their sedentary counterparts. Cardiac dimensions of male swimmers, water polo The degree to which the large heart volumes of endurance players, distance runners, wrestlers, and shot putters were athletes reflect genetic endowment, training adaptations, or a compared during their competitive seasons with those of un- combined effect remains unanswered. trained college men. The swimmers and runners represented Training duration affects cardiac size and structure. athletes in “isotonic” or endurance events; the wrestlers and Several studies report no changes in cardiac dimensionsи with shot putters represented “isometric” or resistance-trained short-term training despite improvements in VO2max and sub- power athletes. TABLE 21.5 shows clear distinctions in struc- maximal exercise heart rate response.167,205 When endurance tural characteristics of the hearts of healthy athletes and un- training increases left ventricular size, the enlargement does trained individuals. Heart structure differences among not reflect a permanent adaptation. Instead, heart size athletes relate to the nature of exercise training. In swimmers, decreases to pretraining levels—with no deleterious effects— left-ventricular volume averaged 181 mL and mass equaled 37,80 as training intensity decreases. FIGURE 21.6 depicts the 308 g. In wrestlers, left-ventricular volume averaged 110 mL general trend for cardiac enlargement (reflected by left- and mass averaged 330 g; the nonathletic controls averaged ventricular mass) in untrained and strengthÐpower- and 101 mL for ventricular volume and 211 g for ventricular endurance-trained athletic groups. mass. The resistance-trained athletes had thicker ventricular walls, whereas the walls of the hearts of endurance athletes Specific Nature of Cardiac Enlargement. The ultra- remained within a normal range. Cardiac morphologic and sonic technique of echocardiography incorporates sound functional adaptations, including resting bradycardia, increased 97818_ch21.qxd 8/4/09 6:00 PM Page 462

462 Section 4 Enhancement of Energy Transfer Capacity

400

350 350g 300 330g 290g 280g 250 260g

200 210g 180g 180g 150 170g

100 130g Figure 21.6 • General trend Left ventricular mass (g) 50 toward cardiac enlargement (left-ventricular mass) among 0 Untrained Endurance College Shot Cyclists Cross-country the untrained and various runners wrestlers putters skiers groups of strength–power- and endurance-trained male and Male Female (where applicable) female athletes.

stroke volume, and enlarged ventricular internal dimensions with normal wall thickness,133,170 with the effect less pro- also occur in prepubertal children who undergo intense en- nounced among females.151 durance training.146 FIGURE 21.7 shows the distribution of left-ventricular end- Training-Induced Plasma Volume Provides a Possible diastolic dimensions in 1309 elite Italian athletes ages 13 to 59 Explanation. Myocardial structural and dimensional adapta- years. These dimensions ranged from 38 to 66 mm (average: tions to regular exercise generally reflect specific training 48.4 mm) in women and 43 to 70 mm (average: 55.5 mm) demands.149,158 As discussed in the section titled “Plasma in men. Ventricular cavity size of the majority of athletes Volume” on page 463, a plasma volume increase within a day remained within normal range, but 14% showed substantially or two of the onset of endurance training contributes to intra- enlarged dimensions. A large body surface area and participa- ventricular enlargement, or eccentric hypertrophy.189 Increased tion in endurance cycling, cross-country skiing, and canoeing plasma volume, coupled with a decreased heart rate and increased represented the major determinants of enlarged cavity dimen- myocardial compliance, dilates or “stretches” the left-ventricular sion. The subjects remained free of heart problems over the cavity analogous to filling a balloon with water. 12-year study period. Other athletic groups also show an en- In contrast to endurance athletes, male and female larged ventricular cavity (increased end-diastolic volume) resistance-trained athletes possess the largest intraventricular

TABLE 21.5 • Comparative Average Cardiac Dimensions in College Athletes, World-Class Athletes, and Normal Subjects College College World-Class College World-Class Runners Swimmers Runners Wrestlers Shot Putters Normals (16 ؍ n) (4 ؍ n) (12 ؍ n) (10 ؍ n) (15 ؍ n) (15 ؍ Dimensiona (n

LVID 54 51 48Ð59b 48 43Ð52b 46 LVV, mL 160 181 154 110 122 101 SV, mL 116 NR 113 75 68 NR LV wall, mm 11.3 10.6 10.8 13.7 13.8 10.3 Septum, mm 10.9 10.7 10.9 13.0 13.5 10.3 LV mass, g 302 308 283 330 348 211

From Morganroth J, et al. Comparative left-ventricular dimensions in trained athletes. Ann Intern Med 1975;82:521. aLVID, left-ventricular internal dimension at end diastole; LVV, left-ventricular volume; SV, stroke volume; LV wall, posterobasal left-ventricular wall thickness; Septum, ventricular septal thickness; LV mass, left-ventricular mass. bRange. NR, Values not reported. 97818_ch21.qxd 8/5/09 12:01 AM Page 463

CHAPTER 21 Training for Anaerobic and Aerobic Power 463

120

100 14% of total 80 Figure 21.7 • Distribution of 60 left-ventricular end-diastolic cavity dimensions in 1309 40 highly trained athletes without evidence of structural

Number of athletes cardiovascular disease. 20 Fourteen percent of the athletes had markedly enlarged 0 left ventricular cavities that 50484644424038 52 54 56 58 60 62 64 66 68 70 ranged in size from 60 to Left-ventricular end-diastolic cavity dimension (mm) 70 mm. (From Pelliccia A, et al. Physiologic left ventricular Male Female cavity dilation in elite athletes. Ann Intern Med 1999;130:23.)

septum, ventricular wall thickness, and ventricular mass, with Exercise training, on the other hand, imposes only a tem- little enlargement in the left ventricle’s internal cavity.56,110 porary myocardial stress, so rest periods provide time for These athletes do not experience volume overload with train- “recuperation.” Also, dilation and weakening of the left ven- ing. Instead, their training produces short-term episodes of tricle, a frequent response to chronic hypertension, does not elevated arterial blood pressure (see Chapter 15) from high accompany compensatory myocardial adaptations with exer- forces generated by a limited mass of skeletal muscle. An in- cise training. The enlarged heart size of elite athletes gener- crease in ventricular wall thickness (that generally falls within ally falls within the upper range of normal for either body size the normal range when expressed as ventricular mass per unit or increased end-diastolic volume. The “athlete’s heart” does body size, particularly fat-free body mass)151,152 compensates not represent a dysfunctional organ. Rather, it demonstrates for additional afterload on the left ventricle without affecting normal systolic and diastolic functions and superior func- ventricular cavity size. More than likely, considerable intra- tional capacity for stroke volume and cardiac output. One individual variability exists for the heart’s structural response possible exception concerns resistance-trained athletes who to different forms of training. When changes do occur, the im- abuse anabolic steroids. An increase in both systolic and dias- plications for myocardial blood supply and long-term cardio- tolic blood pressure, including exacerbation of the normal vascular health remain unknown. No compelling scientific cardiac hypertrophy, occurs with steroid use.64,70,93 evidence indicates that specific modes of arduous physical ac- 95 tivity and training damage a healthy heart. The same also INTEGRATIVE QUESTION pertains to cardiac patients who undergo a proper exercise- based cardiac rehabilitation program.21 Explain how cardiac hypertrophy with pressure overload training (e.g., resistance training) could Functional Versus Pathologic Cardiac Hypertrophy. affect oxygenation of myocardial tissues? Disease can induce considerable cardiac enlargement. In hypertension, for example, the heart chronically works against excessive resistance to blood flow (afterload). This stretches Plasma Volume the heart muscle, which, in accord with the Frank-Starling mechanism, generates compensatory force to overcome the A 12 to 20% increase in plasma volume, in the absence added resistance to systolic ejection. In addition to ventricular of changes in red blood cell mass, occurs after three to six aer- dilation, individual muscle cells enlarge (hypertrophy) to ad- obic training sessions. In fact, a measurable change occurs just to the increased myocardial work imposed by a hyperten- within 24 hours of the first exercise bout, with expansion of sive state. In untreated hypertension, myocardial fibers stretch extracellular fluid volume requiring several weeks.181 beyond their optimal length, so the enlarged, dilated heart Intravascular volume expansion directly relates to increased weakens and eventually fails. To the pathologist, this “hyper- synthesis and retention of plasma albumin.135,142 A plasma trophied” heart represents an enlarged, distended, and func- volume increase enhances circulatory reserve and increases tionally inadequate organ unable to deliver sufficient blood to end-diastolic volume, stroke volume, oxygen transport, и 61,66 satisfy minimal resting requirements. VO2max, and temperature-regulating ability during exercise. 97818_ch21.qxd 8/4/09 6:00 PM Page 464

464 Section 4 Enhancement of Energy Transfer Capacity An expanded plasma volume returns to pretraining levels relationship between heart rate and oxygen consumption during within 1 week following training.189,218 For endurance ath- graded exercise for athletes and sedentary students.178 The letes in different sports, hemoglobin mass and blood volume group of six endurance athletes trained for several years; averaged 35% higher than that of untrained subjects, with lit- the other group consisted of three sedentary college students. tle difference in hemoglobin concentration among groups.75 The researchers evaluated the students’ exercise responses before and after a 55-day training program designed to improve aerobic fitness. The lines relating heart rate and oxygen con- Heart Rate sumption remain essentially linear for both groups throughout Endurance training creates an imbalance between tonic the major portion of the exercise range. Whereas the un- activity of sympathetic accelerator and parasympathetic detrained students’ heart rates accelerate rapidly as exercise pressor neurons in favor of greater vagal dominance—a intensity and oxygen consumption increase, the athletes’ heart response mediated primarily by increased parasympathetic rates rise much less; that is, the slope, or rate of change, of the 60,106 и activity and a small decrease in sympathetic discharge. HRÐVO2 lines differs considerably between trained and un- Training also decreases the intrinsic firing rate of sinoatrial trained. Consequently, an athlete (or trained student) performs (SA) nodal pacemaker tissue.182 These adaptations contribute more intense exercise and achieves a higher oxygen con- to the resting and submaximal exercise bradycardia in highly sumption before reaching a specific submaximal heart rate conditioned endurance athletes or previously sedentary indi- than does a sedentary student. At an oxygen consumption of viduals who train aerobically. 2.0 L и minϪ1, the athletes’ heart rate averaged 70 b и minϪ1 less than for sedentary students. After 55 days of training, the Exercise Heart Rate: Training Effects. Submaximal difference in submaximal heart rate decreased to about heart rate for a standard exercise task frequently decreases by 40 b и minϪ1. In each instance, cardiac output remained essen- 12 to 15 b и minϪ1 with endurance training, while a much tially unchanged—an increase in stroke volume compensated smaller decrease occurs for resting heart rate. Such heart rate for the lower heart rate. reductions reflect the magnitude of training improvement because they generally coincide with increased maximum Stroke Volume stroke volume and cardiac output. FIGURE 21.8 illustrates the Endurance training causes the heart’s stroke volume to increase during rest and exercise regardless of age or gender. Four factors produce this change44,98,131: 200 1. Increased internal left ventricular volume (consequent to the training-induced plasma volume 180 expansion) and mass 2. Reduced cardiac and arterial stiffness 160 3. Increased diastolic filling time (from training- )

–1 induced bradycardia) 140 4. Possibly, improved intrinsic cardiac contractile min

. function 120 Exercise Stroke Volume: Trained Versus Untrained. FIGURE 21.9 shows the stroke volume response during exercise 100 for the men depicted in Figure 21.8. Five important training- related observations emerge: Heart rate (b Heart rate 80 1. The endurance athlete’s heart exhibits a considerably larger stroke volume during rest and exercise than an 60 untrained person of similar age. 2. The greatest stroke volume increase during upright 0 0 1.0 2.0 3.0 4.0 5.0 exercise for trained and untrained persons occurs in Oxygen consumption (L . min–1) transition from rest to moderate exercise. Only small increases in stroke volume accompany further increases in exercise intensity. Endurance athletes 3. Maximum stroke volume generally occurs between Sedentary college students и 40 and 50% of VO (untrained persons); this takes Sedentary college students after training 2max place at a heart rate of 110 to 120 b и minϪ1 in young Figure 21.8 • Heart rate and oxygen consumption during adults. Debate currently focuses on whether the upright exercise in endurance athletes (᭿) and sedentary stroke volume decreases, plateaus, or gradually college students before (᭿) and after (᭿) 55 days of aerobic increases during graded exercise to maximum, par- ϭ training ( ➡ maximal values). ticularly among endurance athletes where the stroke 97818_ch21.qxd 8/4/09 6:00 PM Page 465

CHAPTER 21 Training for Anaerobic and Aerobic Power 465 5. Eight weeks of aerobic training by previously sedentary individuals substantially increases stroke vol- 160 ume, but these values remain below values for elite )

–1 athletes. b

. 140 и Stroke Volume and VO2max. The data in TABLE 21.6 am- 120 plify the importance of strokeи volume in differentiating persons with high and low VO2max values. These data represent 100 three groups: (1) athletes, (2) healthy but sedentary men, and (3) patients with mitral stenosis, a valvular heart disease that 80 causes inadequateи emptying of the left ventricle. The differences in VO2max among groups relate closely to differences troke volume (mL S troke volume (mL in maximal stroke volume. Patients with mitral stenosis 0 0 1.0 2.0 3.0 4.0 5.0 achieved an aerobic capacity and maximum stroke volume Oxygen consumption (L . min–1) one-half that of sedentary subjects. The importance of stroke volume also emerges in comparisons amongи healthy groups. Athletes achieved an average 62% larger VO than seden- Endurance athletes 2max tary subjects, almost entirely from the athletes’ 60% larger Sedentary college students stroke volume and cardiac output (Figs. 21.9 and 21.10). Sedentary college students after training Cardiac Output Figure 21.9 • Stroke volume and oxygen consumption during upright exercise in endurance athletes (᭿) and An increase in maximum cardiac output represents the sedentary college students before (᭿) and after (᭿) 55 days most significant adaptation in cardiovascular function with ϭ of aerobic training ( ➡ maximal values). aerobic training. Maximal heart rate generally decreases slightly with training; thus, increased cardiac output capacity volume may benefit from an enlarged plasma results directly from improved stroke volume. A large maxi- volume.62,219 More than likely, endurance training mum cardiac output (stroke volume) distinguishes champion minimizes the small decrease in stroke volume often endurance athletes from other well-trained athletes and from observed during maximal exercise. Even at near- untrained counterparts. maximal heart rates, sufficient time exists for the FIGURE 21.10 illustrates the important role of cardiac out- trained heart’s ventricles to fill during diastole with- put in achieving a high level of aerobic metabolism. In trained out reduction in stroke volume.59,197,228 athletes and students, cardiac output increases linearly with 4. For untrained persons, only a small increase in stroke oxygen consumption throughout the major portion of the volume occurs during transition from rest to exer- exercise intensity range with the athletes achieving the high- cise. Consequently, a cardiac output increase occurs est values for both variables. A linear relationship between from acceleration in heart rate. For endurance ath- cardiac output and oxygen consumption in graded exercise letes, heart rate and stroke volume both increase to also occurs in children and adolescents. For these young per- increase cardiac output; the athlete’s stroke volume sons, increased stroke volume (and proportionate increase in generally expands 60% above resting values. cardiac output) closely matches the added oxygen require- Relatively large stroke volume increases in transition ment of exercise during growth.34 from rest to exercise also occur in endurance-trained children and older men compared with healthy but Exercise Training and Submaximal Cardiac Output. untrained counterparts.66,176 Early reports showed that endurance training, while improving

TABLE 21.6 • Maximal Values for Oxygen Consumption, Heart Rate, Stroke Volume, and Cardiac Output in Three Groups with Low, Normal, and High Aerobic Capacities V˙ O Max Heart Rate Max Stroke Volume Max Cardiac Output 2max؊ ؊ ؊ ؊ Group (L и min 1) (B и min 1) (mL и B 1) (L и min 1)

Mitral stenosis 1.6 190 50 9.5 Sedentary 3.2 200 100 20.0 Athlete 5.2 190 160 30.4

Modified from Rowell LB. Circulation. Med Sci Sports 1969;1:15. 97818_ch21.qxd 8/4/09 6:00 PM Page 466

466 Section 4 Enhancement of Energy Transfer Capacity

30 20 ) –1 erence min ff . 20 10 di

per dL blood) per dL

2 2 a-vO

(mL O (mL 0 10 0 1.0 2.0 3.0 4.0 5.0 Oxygen consumption (L . min–1) ardiac output (L ardiac output (L C Endurance athletes 0 Sedentary college students 0 1.0 2.0 3.0 4.0 5.0 Sedentary college students after training Oxygen consumption (L . min–1) _ Figure 21.11 • The a-vO2 difference and oxygen Endurance athletes consumption during upright exercise in endurance athletes Sedentary college students (᭿) and sedentary college students before (᭿) and after (᭿) ϭ Sedentary college students after training 55 days of aerobic training ( ➡ maximal values).

Figure 21.10 • Cardiac output and oxygen consumption _ during upright exercise in endurance athletes (᭿) and The a-vO2 difference for the students increases steadily dur- sedentary college students before (᭿) and after (᭿) 55 days ing graded exercise to a maximum of 15 mL per deciliter of ϭ of aerobic training ( ➡ maximal values). blood. Following 55 days of training, the students’ maximum oxygen extraction increased 13% to 17 mL of oxygen. This maximal cardiac output, reduced the heart’s minute volume means that during intense exercise, arterial blood released ap- during moderate exercise. In one study, average cardiac out- proximately 85% of its oxygen content. Actually, the active _ put of young men after 16 weeks of aerobic training de- muscles extract even more oxygen because the a-vO2 differ- Ϫ creased by 1.1 and 1.5 L и min 1 at a specific submaximal ence reflects an average based on sampling of mixed-venous oxygen consumption.42 As expected, maximal cardiac output blood, which contains blood returning from tissues that use Ϫ increased 8%, from 22.4 to 24.2 L и min 1. With reduced sub- much less oxygen during exercise than active muscle. The _ maximal cardiac output, a corresponding increase in oxygen posttraining value for maximal a-vO2 difference for the stu- extraction in the active muscles achieves the exercise oxygen dents equals the value of the endurance athletes. Obviously, requirement. A training-induced reduction in submaximal car- the students’ lower cardiacи output capacity explains the rather diac output presumably reflects two factors: large difference in VO2max that clearly differentiates athletes from students. 1. More effective redistribution of blood flow 2. Trained muscles’ enhanced capacity to generate ATP aerobically at a lower tissue PO2 Blood Flow and Distribution _ Submaximal Exercise. Trained persons perform sub- Oxygen Extraction (a-vO2 Difference) maximal exercise with a lower cardiac output (and unchanged or slightly lower muscle blood flow) than untrained persons. Aerobic training increases the quantity of oxygen ex- A relatively larger portion of submaximal cardiac output tracted (measured as arterio-venous oxygen differences, or _ flows to high oxidative skeletal muscles (composed primarily a-vO difference) from circulating blood.183 An increase in the 2 _ of type I fibers) at the expense of blood flow to muscles with maximum a-vO difference results from more effective cardiac 2 a large percentage of type IIb fibers with low oxidative output distribution to active muscles combined with enhanced capacity.35 Two factors contribute to reduced muscle blood capacity of trained muscle fibers to extract and process available _ flow in submaximal exercise:103,204,217,225 oxygen, The a-vO2 difference takes on even greater importance in contributing to improved aerobic capacity with training in 1. Relatively rapid training-induced changes in vasoac- older men and women because the elderly often show dimin- tive properties of large arteries and local resistance ves- ished capacity to improve cardiac output with training.100,185 sels within skeletal and cardiac muscle, mediated by FIGURE 21.11 compares the relationship between oxygen the dilation effects of endothelium-derived nitric oxide _ extraction (a-vO2 difference) and exercise intensity for the 2. Changes within muscle cells that enhance oxidative trained athletes and untrained students depicted in Figure 21.8. capacity 97818_ch21.qxd 8/4/09 6:00 PM Page 467

CHAPTER 21 Training for Anaerobic and Aerobic Power 467 Both of these adaptations support the principle of train- The significance of vascular and cellular adaptations to ing specificity. As the muscle’s ability to deliver, extract, and the heart’s functional capacity during exercise remains use oxygen increases, the active tissue’s oxygen needs require unclear—mainly because the healthy, untrained heart does proportionally less blood flow. not suffer from reduced oxygen during maximal exercise. Training adaptations may provide some cardioprotection by Maximal Exercise. Three factors affect how aerobic enabling myocardial tissue to better tolerate and recover from training increases total skeletal muscle blood flow during transient episodes of ischemia (i.e., become more resistant to maximal exercise: ischemic injury). The trained tissue also functions at a lower 1. Larger maximal cardiac output percentage of its total oxidative capacity during exercise. 2. Distribution of blood to muscle from nonactive areas Vascular adaptations do not accompany the myocardial 137 that temporarily compromise blood flow during all- hypertrophy that occurs with chronic resistance training. out effort 3. Enlargement of cross-sectional areas of large and Blood Pressure small arteries (arteriogenesis) and veins, and 10 to 20% increase in capillarization per gram of muscle Regular aerobic training reduces systolic and diastolic (angiogenesis).77,164,168 This effect begins rapidly blood pressure during rest and submaximal exercise. The from increased vascular endothelial growth factors— largest reduction occurs in systolic pressure, particularly in produced by skeletal muscle cells (partly in response hypertensive subjects (see Chapters 15 and 32 for a more to vascular sheer stress and wall stress in response to complete discussion). the hemodynamic forces imposed by exercise) to induce angiogenesis—after a single bout of exercise in Pulmonary Adaptations with Training trained and untrained persons.54,97,104 Aerobic training stimulates adaptations in pulmonary venti- Training-induced decreases in splanchnic and renal lation dynamics during submaximal and maximal exer- blood flow in exercise occur from reduced sympathetic nerv- cise. The adaptations generally reflect a breathing strategy 128 ous system outflow to these tissues. This frees a relatively that minimizes respiratory work at a given exercise intensity. large quantity of blood for distribution to active muscles. This frees oxygen for use by the nonrespiratory active Concurrently, exercise training and accompanying exposure musculature. to elevated core temperatures produces heat loss adaptations via enhanced endothelium-dependent increases in skin blood flow for a given internal temperature.89,99 Augmented cuta- Maximal Exercise neous blood flow facilitates the endurance-trained person’s Maximal exercise ventilation increases from increased capacity to dissipate the metabolic heat generated in exercise. tidal volume and breathing rate as maximal oxygen consump- The observation that oxygen extraction in skeletal mus- tion increases. This makes sense physiologically because any cle remains near maximal in intense exercise supports the и increase in VO2max raises the body’s oxygen requirement and hypothesis that oxygen supply (blood flow), not oxygen use corresponding need to eliminate additional carbon dioxide via (extraction), limits the maximal respiratory rate of muscle alveolar ventilation. tissue.10,139,168

Myocardial Blood Flow. For both normal persons and Submaximal Exercise cardiac patients, structural and functional changes in the Several weeks of aerobic training reduce the ventilatory heart’s vasculature, including modifications in mechanisms и и equivalent for oxygen (V /VO ) during submaximal exercise that regulate myocardial perfusion, parallel a modest training- E 2 and lower the percentage of the total exercise oxygen cost at- induced myocardial hypertrophy.69,102 Structural vascular tributable to breathing. Reduced oxygen consumption by the modifications include an increase in cross-sectional area of the ventilatory musculature enhances exercise endurance for two proximal coronary arteries, possible arteriolar proliferation reasons: and longitudinal growth, recruitment of collateral vessels, and increased capillary density. These adaptations provide ade- 1. It reduces fatiguing effects of exercise on the ventila- quate perfusion to support the increased blood flow and energy tory musculature. demands of the functionally improved myocardium. 2. Any oxygen freed from use by the respiratory Two mechanisms help explain how aerobic training in- musculature becomes available to active locomotor creases coronary blood flow and capillary exchange capacity: muscles. 1. Ordered progression of structural remodeling that In general, exercise training increases tidal volume and improves myocardial vascularization when new cap- decreases breathing frequency. Consequently, air remains in illaries form and develop into small arterioles101 the lungs for a longer time between breaths; this increases 2. More effective control of vascular resistance and oxygen extraction from inspired air. For example, the exhaled blood distribution within the myocardium211,217 air of trained individuals during submaximal exercise contains 97818_ch21.qxd 8/4/09 6:00 PM Page 468

468 Section 4 Enhancement of Energy Transfer Capacity Training May Benefit Ventilatory Endurance Arm-training group Arm work Leg work Prolonged, intense exercise causes the inspiratory mus- 40 cles to fatigue.8,86 Such exercise also reduces the abdominal muscles’ capacity to generate maximal expiratory pressure.51 30 Exercise training allows for sustained, exceptionally high levels of submaximum ventilation.19,88,193 Endurance ) 2 20 training stabilizes the body’s internal milieu during submaximal exercise. Consequently, exercise causes less disruption in / VO

E 10 whole-body hormonal and acidÐbase balance that could nega- (V

tively impact inspiratory muscle function. The ventilatory muscles also benefit directly from exercise training. For 0 LI LI example, 20 weeks of run training by healthy men and women Leg-training group improved ventilatory muscle endurance by approximately 16% (less lactate accumulation during standard breathing Arm work Leg work 40 exercise). The training-induced increase in aerobic enzyme levels and oxidative capacity of the respiratory musculature 163,196 30 contribute to enhanced ventilatory muscle function. Exercise training also increases inspiratory muscle capacity to Ventilation equivalent Ventilation 20 generate force and sustain a given level of inspiratory pressure.26 These adaptations benefit exercise performance in three ways: 10 1. Reduce overall exercise energy demands because of 0 less respiratory work LI LI 2. Reduce lactate production by the ventilatory muscles during intense, prolonged exercise 3. Enhance how ventilatory muscles metabolize circu- Before training After training lating lactate as metabolic fuel Figure 21.12 • Ventilation equivalents during light (L) and intense (I) submaximal arm and leg exercise before and after Blood Lactate Concentration arm training (top) and leg training (bottom). (From Rasmussen B, et al. Pulmonary ventilation, blood gases, and FIGURE 21.13 illustrates the generalized effect of endurance blood pH after training of the arms and the legs. J Appl training in lowering blood lactate levels and extending exer- Physiol 1975;38:250.) cise before onset of blood lactate accumulation (OBLA)

only 14 to 15% oxygen, whereas the expired air of untrained persons averages 18% at the same exercise intensity. This translates to the common observation that untrained persons ventilate proportionately more air to achieve the same sub- 7 maximal oxygen consumption. Substantial specificity exists for ventilatory responses 6 relative to the type of exercise and training adaptations. When 5 subjects performed arm-only and leg-only exercise, consis- Pre-training lactate tently higher ventilatory equivalents occurred with the arms 4 (FIG. 21.12). As expected, the ventilatory equivalent decreased in each mode with exercise training. However, the reduction 3 occurred only with exercise that used specifically trained 2 muscles. For the group trained by arm-crank ergometry, the Blood lactate (mM) ventilation equivalent decreased only during arm exercise and 1 vice versa for the leg-trained group. The ventilatory training Post-training lactate 0 adaptation linked closely to a less pronounced rise in blood 0 1.0 2.0 3.0 lactate and heart rate during the specific training exercise. Oxygen consumption (L . min–1) This suggests that local adaptations in specifically trained muscles affect the ventilatory adjustment to training. In this Figure 21.13 • Generalized response for pre- and regard, lower lactate levels with training remove the drive to posttraining lactate accumulation during graded exercise. breathe from any additional carbon dioxide produced from (Plots based on data from the Applied Physiology Laboratory, lactate buffering. University of Michigan, Ann Arbor, MI.) 97818_ch21.qxd 8/4/09 6:00 PM Page 469

CHAPTER 21 Training for Anaerobic and Aerobic Power 469 during exercise of increasing intensity. The underlying expla- и VO . In the performance test, subjects attempted nation centers on three possibilities related to central and 2max to maintain a constant power output of 265 watts peripheral adaptations to aerobic training discussed in this for 8 minutes. Training produced less drop-off in chapter: power output during the prescribed 8-minute 1. Decreased rate of lactate formation during exercise exercise test. 2. Increased rate of lactate clearance (removal) during ¥ Psychologic benefits: Regular exercise, regardless of exercise age, creates important potential benefits on psycho- 3. Combined effects of decreased lactate formation and logic state. Adaptations often occur to a degree equal increased lactate removal to that achieved with other therapeutic interventions, including pharmacologic therapy.45,206

Other Aerobic Training Adaptations ¥ Body composition changes: Regular aerobic exercise Six Potential Psychologic Benefits from for the obese or overweight person reduces body Regular Exercise mass and body fat and augments a more favorable 1. Reduction in state of anxiety (i.e., the level of body fat distribution (see Chapter 30). Exercise only anxiety at the time of measurement) or combined with calorie restriction reduces body fat 2. Decrease in mild-to-moderate depression more than weight loss with dieting by promoting con- 3. Reduction in neuroticism (long-term exercise) servation of lean tissue. 4. Adjunct to professional treatment of severe ¥ Body heat transfer: Well-hydrated, trained individu- depression als exercise more comfortably in hot environments 5. Improvement in mood, self-esteem, and self- because of a larger plasma volume and more respon- concept sive thermoregulatory mechanisms; in other words, 6. Reduction in the various indices of stress they dissipate heat faster and more economically than sedentary individuals. ¥ Performance changes: Enhanced endurance performance accompanies physiologic adaptations with train- Summary View ing. FIGURE 21.14 depicts cycling performance prior to and following 10 weeks of cycling training for 40 to FIGURE 21.15 summarizesи adaptive changes in active muscle that 60 minutes, 4 days per week for 10 weeks at 85% accompany VO2max improvements with endurance training and detraining. Aerobic capacity generally increases 15 to 25% over the first 3 months of intensive training and may improveи by 50% over a 2-year interval. When training ceases, VO2max rapidly decreases toward the pretraining level. Even more im- 0 pressive training effects occur for aerobic enzymes of the citric acid cycle and electron-transport chain within the mitochondria 5 of trained muscles. These enzymes increase rapidly and sub- After training stantially throughout training in both fiber types and subdivi- 10 sions. Conversely, a few weeks of detraining substantially reduce a large portion of enzymatic adaptations. The number of ork rate 15 muscle capillaries increases during training. When training

g e drop-o ff 20 ceases, this adaptation in blood supply probably decreases relatively slowly. The ultimate detraining occurs with aging. 25 Although it is possible to produce substantial improvements in Before training physiologic function in the elderly, regular exercise slows but rom initial w Percenta f 30 cannot halt the muscle atrophy, weakness, and fatigability that accompanies an increase in chronological age.43 35 Local metabolic improvement greatly exceeds improvements in capacityи to circulate, deliver, and use oxygen 02341 5678 (reflected by VO2max and cardiac output) during intense exercise. With local training adaptations, a muscle’s lactate flux Exercise duration (min) remains at lower levels (lower production and/or greater removal rate) than similar submaximal exercise before train- Figure 21.14 • Percentage drop-off from initial exercise intensity before and after 10 weeks of endurance cycling ing. These cellular adjustments account for how a trained training. (From the Applied Physiology Laboratory, University personи performs steady-rate exercise at a greater percentage of Michigan, Ann Arbor, MI.) of VO2max. 97818_ch21.qxd 8/4/09 6:00 PM Page 470

470 Section 4 Enhancement of Energy Transfer Capacity

2.2 Aerobic enzymes

2.0

1.8

Oxidative potential of FT fibers 1.6 Glycogen

1.4 Capillaries Figure 21.15 • Generalized Adaptive/Control Ratio VO2max summary of increase in aerobic 1.2 capacity and muscle adaptations with endurance Cross-section size of ST fibers training. (Modified from Saltin 1.0 B, et al. Fiber types and metabolic potentials of skeletal 0 1 2 6 12 18 24 6 muscles in sedentary man and Control Training duration (months) No training endurance runners. Ann NY Acad Sci 1977;301:3.) FACTORS THAT AFFECT AEROBIC Training Intensity TRAINING RESPONSES Training-induced physiologic adaptations depend primarily Four factors influence the aerobic training response: on intensity of overload. At least seven different ways express exercise intensity: 1. Initial level of aerobic fitness и Ϫ1 2. Training intensity 1. Energy expended per unit time (e.g., 9 kCal min , и Ϫ1 3. Training frequency or 37.8 kJ min ) 4. Training duration 2. Absolute exercise level or power output (e.g., cycle at 900 kg-m и minϪ1, or 147 W) 3. Relativeи metabolic иlevel expressed as percentage of Initial Level of Aerobic Fitness VO2max (e.g., 85% VO2max) 4. Exercise below, at, or above the lactate threshold, or The magnitude of the training response depends on initial fit- OBLA (e.g., 4 mM lactate) ness level. Someone who rates low at the start has consider- 5. Exercise heart rate, or percentage of maximum heart able room for improvement. If capacity already rates high, the и Ϫ1 rate (e.g., 180 b min , or 80% HRmax) magnitude of improvement remains relatively small. Studies 6. Multiples of resting metabolic rate (e.g., 6 METs) ofи sedentary, middle-aged men with heart disease showed that 7. Rating of perceived exertion (e.g., RPE ϭ 14) VO2max improved by 50%, while similar training in normally active, healthy adults improved 10 to 15%.168 Of course, a rel- An example of absolute training intensity involves hav- atively small improvement in aerobic capacity represents as ing all individuals exercise at the same power output, or en- Ϫ crucial a change for an elite athlete (where even a 1 to 2% per- ergy expenditure (e.g., 9.0 kCal и min 1) for 30 minutes. formance change could be the difference between winning When everyone performs at the same intensity, the task can and losing) as a much larger increase in physiologic and per- elicit considerable stress for one person yet fall short of train- formance capacity for a sedentary person. As a general guide- ing threshold for another more fit person. For this reason, the line, aerobic fitness improvements with endurance training relative stress on a person’s physiologic systems establishes range between 5 and 25%. Some of this improvement occurs exercise intensity. The assigned exercise intensity usually re- within the first week of training. lates to some breakpoint for steady-rate exercise (e.g., lactate threshold, OBLA) or someи percentage of maximum physiologic capacity (e.g., %VO , %HR ), or maximum exer- INTEGRATIVE QUESTION 2max max cise capacity. General practice establishes aerobicи training Respond to the question, “How long must I intensity via direct measurement (or estimation) of VO2max (or exercise to ‘get in shape’?” HRmax) and then assigns an exercise level to correspond to some percentage of maximum. 97818_ch21.qxd 8/4/09 6:00 PM Page 471

CHAPTER 21 Training for Anaerobic and Aerobic Power 471 This approach to determining heart rate training thresh- TABLE 21.7 • Relationship Between old creates a somewhat higher value than computing the Percentage Maximal Heart threshold heart rate as 70% of HRmax. Rate and Percentage V˙ O2max Clearly, achieving positive training adaptations does not Percentage HR Percentage V˙ O require strenuous exercise. For most healthy persons, an exer- max 2max cise heart rate of 70% maximum represents moderate exercise 50 28 with no discomfort. This training level, frequently referred to 60 40 as moderate “conversational exercise,” achieves sufficient 70 58 intensity to stimulate a training effect yet does not produce a 80 70 level of discomfort (e.g., lactate accumulation and associated 90 83 hyperpnea) that prevents talking during the workout. A previ- 100 100 ously sedentary person need not exercise above this threshold heart rate to improve physiologic capacity. FIGURE 21.16 shows that as aerobic fitness improves, submaximal exercise heart rate decreases 10 to 20 b и minϪ1 for a Establishing training intensity from measures of oxygen given level oxygen consumption. To keep pace with physio- consumption provides a high degree of accuracy, but its use logic improvement, the exercise level must increase periodi- requires sophisticated monitoring that renders this method cally to achieve the desired exercise heart rate. A person begins impractical for general use. An effective alternative relies on training by walking, then walks more briskly; jogging then re- heart rate to classify exercise for relative intensity when indi- places walking for periods of the workout; and eventually con- vidualizing training programs. Exercise heart rate is conven- и tinuous running elicits the desired exercise heart rate. In each ient because %VO and %HR relate in a predictable 2max max progression, exercise remains at the same relative intensity. If way regardless of gender, race, fitness level, exercise mode, exercise intensity progression does not adjust to training im- or age. Exercise training does not affect a particular individ- и provements, the exercise program essentially becomes a lower- ual’s heart rate at a given %VO , so there is little or no 2max intensity maintenance program for aerobic fitness. need to frequently test or adjust the exercise prescription relative to training-induced changes in aerobic capacity as long as 192 Is Strenuous Training More Effective? exercise at the %HRmax is maintained. и TABLE 21.7 presents selected values for %VO2max and Generally, the higher the training intensity above thresh- 4,127 и corresponding %HRmax obtained from several sources. old, the greater the training improvement for VO2max, particu- и 63 The error in estimating %VO2max from %HRmax, or vice versa, larly when the volume of exercise is controlled. Although equals about 8%. Thus, one need only monitorи heart rate to minimal threshold intensity exists below which no meaningful estimate the relative exercise stress, or %VO2max, within the training effect occurs, a “ceiling” may also exist above which givenи error range. The relationship between %HRmax and no further gains accrue. More fit men and women generally re- %VO2max remains essentially the same for arm or leg quire higher threshold levels to stimulate a training response exercises among healthy subjects, normal-weight and obese than less fit persons. The ceilingи for training intensity remains persons, cardiac patients, and persons with spinal cord unknown, although about 85% VO2max (corresponding to 90% 48,83,132 injuries. Importantly, arm (upper-body) exercise pro- HRmax) probably represents an upper limit. Importantly, regard- duces lower HRmax than leg exercises. One must consider this less of the exercise level selected, more does not necessarily difference when formulating an individualized exercise pre- produce greater (or faster) results. Excessive training intensity scription for different exercise modes (see p. 473). and abrupt increases in training volume increase risk for injury to bones, joints, and muscles.3,90 For men and women, the number of miles run per week represents the only variable consis- Train at a Percentage of HR max tently associated with running injuries. In preadolescent Aerobic capacity improves if exercise intensity regularly children, running excessive distances strains the articular carti- maintains heart rate between 55 and 70% of maximum. lage, which could injure the bone’s growth plate (epiphysis) During lower-body exercise such as cycling, walking, or run- and adversely affect normal growth and development. ning,и this heart rate increase equals about 40 to 55% of the VO2max; for college-aged men and women, the training heart Determining the “Training-Sensitive Zone” rate ranges from 120 to 140 b и minϪ1. One can determine maximum exercise heart rate imme- An alternative and equally effective method to establish diately after several minutes of all-out exercise. This exercise the training threshold, termed the Karvonen method, intensity requires considerable motivation and stress—a re- requires that subjects exercise at a heart rate equal to 60% quirement inadvisable for adults without medical clearance, of the difference between resting and maximum.94 With particularly those predisposed to coronary heart disease. Most the Karvonen method, one computes training heart rate as individuals should use age-predicted maximum heart rates follows: presented in FIGURE 21.17 because these tables are based on ϭ ϩ Ϫ HRthreshold HRrest 0.60 (HRmax HRrest) averages in population studies. 97818_ch21.qxd 8/4/09 6:00 PM Page 472

472 Section 4 Enhancement of Energy Transfer Capacity

200

180

160 Before training ) –1 140 min .

120 After training

100 Heart rate (b Heart rate

80 Figure 21.16 • Improvement in exercise heart rate response 60 with aerobic training in relation to oxygen 0 consumption. A reduction in 0 22 24 26 28 30 32 34 36 38 40 exercise heart rate with Oxygen consumption (mL . kg–1 . min–1) training usually reflects enhanced stroke volume.

200 200 195 Age-predicted maximum heart rate 190 190 90% level 185 180 180 180 175 175 171 170 ) 170 166 –1 162 165 160 158 min

. 160 153 155 150 Training-sensitive zone148 150 144 140 140 140 135 136

Heart rate (b Heart rate 130 133 129 120 126 120 122 119 117 116 110 114 111 112 70% level 108 109 105 100 102 105 60% level 93 99 90 Figure 21.17 • Maximal heart 96 rates and training-sensitive 20 25 30 35 40 45 50 55 60 65 70 zone for aerobic training of Age (years) men and women of different ages. 97818_ch21.qxd 8/4/09 6:00 PM Page 473

CHAPTER 21 Training for Anaerobic and Aerobic Power 473

While individuals of a given age have varying HRmax a convenient rule of thumb, but it does not determine a spe- values, the inaccuracy from individual variation (Ϯ10 b и cific person’s maximum heart rate. For example, within Ϫ1 min standard deviation for any age-predicted HRmax) has normal variation limits and using the 220-minus-age formula, little influence in establishing effective training for healthy the actual maximum heart rate of 95% (Ϯ2 standard devia- persons. Maximum heart rate has commonly been estimated tions) of 40-year-old men and women ranges between as 220 minus age in years, with values independent of race or 160 and 200 b и minϪ1. Figure 21.17 also depicts the gender in children and adults.87,114,115 “training-sensitive zone” related to age. A 40-year-old woman or man who wants to train at HR ϭ 220 Ϫ age (y) max moderate intensity but still achieve the threshold level would select a training heart rate equal to 70% of age-predicted Perhaps a Modification Is Required. Recent evidence HRmax. Using the 220-minus-age formula results in a target from a longitudinal study of 132 persons measured an average Ϫ exercise heart rate of 126 b и min 1 (0.70 ϫ 180). To increase of 7 times over 9 years indicates a bias in the above prediction training to 85% of maximum, exercise intensity must increase of HR . The bias overestimates this measure in men and Ϫ max to produce a heart rate of 153 b и min 1 (0.85 ϫ 180). women under the age of 40 years and it underestimates in 55 those older than 40 years (FIG. 21.18). This prediction Running Versus Swimming and Other Forms of equation (with a standard deviation of 5 to 8 beats per Upper-Body Exercise. Estimation of HR requires an minute), independent of sex, BMI, and resting heart rate is as max adjustment when swimming or performing other upper-body follows: exercises. Maximum heart rate during these exercise modes ϭ Ϫ ϫ и Ϫ1 HRmax 206.9 0.67 age (y) averages about 13 b min lower for trained and untrained men and women than while running.48,57,129 This difference For example, the above equation can estimate maximum probably results from less feed-forward stimulation from the heart rate for a 30-year-old man or woman: motor cortex to the medulla during swimming, in addition to ϭ Ϫ ϫ HRmax 206.9 (0.67 30) less feedback stimulation from the smaller, active upper-body ϭ 206.9 Ϫ 20.1 muscle mass. In swimming, the horizontal body position and Ϫ cooling effect of the water may also contribute to a lower ϭ 187 b и min 1 HRmax. This prediction agrees closely with other research in the Establishing the appropriate exercise intensity for swim- area.114,202 Chapter 32 continues the discussion of the affects ming and upper-body exercise requires subtracting 13 b и Ϫ1 of age on maximum heart rate. min from the age-predicted HRmax in Figure 21.17. A These prediction formulas associate with a plus/minus 30-year-old person who chooses to swim at 70% HRmax error and should be used with caution. Each formula represents should select a swimming speed that produces a heart rate of )

–1 195

min 185

175

165

Figure 21.18 • 155 Modified maximum heart rate versus age 145 prediction compared Maximum heart rate (b Maximum heart rate with the commonly 135 used equation of 220 – Age (y) 30 35 40 45 50 55 60 65 70 75 age. (From Gellish RL, 220 — Age 190 185 180 175 170 165 160 155 150 145 et al. Longitudinal 206.9 — 0.67 x Age 187 183 180 177 173 170 167 163 160 157 modeling of the Age-predicted maximum heart rates relationship between age and maximal heart 220 — Age 206.9 — 0.67 x Age rate. Med Sci Sports Exerc 2007;39:822.) 97818_ch21.qxd 8/4/09 11:15 PM Page 474

474 Section 4 Enhancement of Energy Transfer Capacity

124 b и minϪ1 (0.70 ϫ [190 Ϫ 13]). This would more accurately represent the proper threshold heart rate for swimming RPE Scale Equivalent Equivalent to induce a training effect. Without this heart rate adjustment, % HRmax % VO2max a prescription of upper-body exercise based on %HRmax in leg exercise overestimates the appropriate threshold training heart rate. 6 7 Very, very light 8 Is Less Intense Training Effective? 9 Very light 10 The often-cited recommendation of 70% HRmax as a training threshold for aerobic improvement represents a gen- 11 Fairly light 52-66 31-50 eral guideline for effective yet comfortable exercise. The 12 lower limit may depend on the participant’s initial exercise 13 Somewhat hard 61-85 51-75 capacity and current state of training. In addition, older and 14 less fit, as well as sedentary, overweight men and women 15 Hard 86-91 76-85 haveи training thresholds closer to 60% HRmax (about 16 45% VO2max). Twenty to 30 minutes of continuous exercise at 17 Very hard 92 85 70% HRmax stimulates a training effect; exercise at the lower 18 intensity of 60% HRmax for 45 minutes also proves beneficial. 19 Very, very hard Generally, longer exercise duration offsets lower exercise intensity in terms of benefits. Figure 21.19 • The Borg scale (and accompanying estimates of relative exercise intensity) for obtaining the RPE during Train at a Perception of Effort exercise. (Modified from Borg GA. Psychological basis of physical exertion. Med Sci Sports Exerc 1982;14:377.) The rating of perceived exertion (RPE) can be used in addition to oxygen consumption, heart rate, and blood lactate to indicate exercise intensity.15,173 With this psychophysiologic approach, the exerciser rates on a numerical scale perceived determine the appropriate activity level by plotting intensity feelings relative to exertion level. Monitoring and adjusting (e.g., running speed) in relation to blood lactate level. In this RPE during exercise provides an effective way to prescribe example, the running speed to produce a blood lactate con- exercise from an individual’s perception of effort that coin- centration at the 4-mM level (OBLA) represented the recom- cides with objective measures of physiologic/metabolic strain и mended training intensity. Many coaches use the 4-mM blood (%HR , %VO , blood lactate concentration). max 2max lactate level as the optimal aerobic training intensity, yet no con- Exercise that corresponds to higher levels of energy vincing evidence exists to justify this particular blood lactate expenditure and physiologic strain produces higher RPE ratings. For example, an RPE of 13 or 14 (exercise that feels “somewhat hard;” FIG. 21.19) coincides with about 70% HRmax during cycle ergometer and treadmill exercise; an RPE between 11 and 12 corresponds to exercise at the lactate threshold for trained and untrained individuals. The RPE establishes an exercise prescription for exercise intensities that correspond to blood lactate concentrations of 2.5 mM (RPE ~ 15) and 4.0 mM (RPE ~ 18) during a 30-minute treadmill run where subjects self-regulated exercise intensity.200 Individuals learn quickly to exercise at a specific RPE. In similar fashion, a simple “talk test” that asks whether comfortable speech is possible produces exercise intensities within accepted guidelines for exercise prescription for treadmill and cycle ergometer exercise.153

Train at the Lactate Threshold Figure 21.20 • Blood lactate concentration in relation Exercising at or slightly above the lactate threshold pro- to running speed for one subject. At a lactate level of vides yet another effective aerobic training method. The 4.0 mM, the corresponding running speed was approximately Ϫ higher exercise levels produce the greatest benefits, particu- 13 km и h 1. This speed establishes the subject’s initial 113,220 larly for fit individuals. FIGURE 21.20 illustrates how to training intensity. 97818_ch21.qxd 8/4/09 6:00 PM Page 475

CHAPTER 21 Training for Anaerobic and Aerobic Power 475

159 level as “ideal.” Regardless of the specific blood lactate level or duration. Studies using intervalи training show that train- chosen for endurance training, the blood lactateÐexercise in- ing 2 days a week produced VO2max changes similar to train- tensity relationship should be evaluated periodically, with ex- ing 5 days weekly.47 In other studies that maintained a ercise intensity adjusted as fitness improves. If regular blood constantи total exercise volume, no differences emerged in lactate measurement proves impractical, the exercise heart VO2max improvement between training frequencies of 2 and rate at the initial lactate determination remains a convenient 4 or 3 and 5 days a week.191 As with training duration, more- and relatively stable marker to set an appropriate predeter- frequent training produces beneficial effects when training mined exercise intensity. During incremental exercise, no sys- occurs at a lower intensity. tematic training-induced change occurs in the heart While the extra time invested to increase training fre- 46 и rateÐblood lactate relationship. quency may not prove profitable for improving VO2max, the The RPE provides an effective tool to estimate blood lac- extra quantity of exercise (e.g., 3 vs. 6 days per week) often tate threshold when establishing training intensity for continu- represents a considerable caloric expenditure with concomi- ous exercise. However, a change in the blood lactate tant improvements in well-being and health. To produce concentrationÐRPE relationship does occur with repeated meaningful weight loss through exercise, each exercise ses- exercise bouts. The relationship remains altered from a single sion should last at least 60 minutes at sufficient intensity to exercise bout, even after 3.5 hours of recovery.221 This limits expend 300 kCal or more. Training only 1 day a week gener- RPE to gauge exercise intensity for a specific blood lactate con- ally does not meaningfully change anaerobic or aerobic ca- centration if repeated bouts of exercise occur during the same pacity, body composition, or body weight.5 training session (e.g., during interval training; see p. 480). Typical aerobic training programs take place 3 days a One important distinction between %HRmax and lactate week, usually with a single rest day separating workout days. threshold for setting training intensity lies in the physio- One could reasonably ask whether training on consecutive logic dynamics each method reflects. The %HRmax method days would produce equally effective results. In an experi- establishes a level of exercise stress to overload the central ment concernedи with this question, nearly identical improve- circulation (e.g., stroke volume, cardiac output), whereas the ments in VO2max occurred regardless of sequencing of the capability of the peripheral vasculature and active muscles to 3-days-per-week training schedule.136 Thus, the stimulus for sustain steady-rate aerobic metabolism dictates exercise in- aerobic training probably links closely to exercise intensity tensity adjustments based on lactate threshold. and total work accomplished, not to the sequencing of training days.

Training Duration Exercise Mode No threshold duration per workout exists for optimal aerobic Maintaining constancy for exercise intensity, duration, and improvement. If a threshold exists, it likely depends on the in- frequency produces a similar training response independent teraction of total work accomplished (duration or training vol- of training mode—provided exercise involves relatively large ume), exercise intensity, training frequency, and initial fitness muscle groups. Bicycling, walking, running, rowing, swim- level. For previously sedentary adults, a dose response rela- ming, in-line skating, rope skipping, bench-stepping, stair tionship may exist.25 A 3- to 5-minute daily exercise period climbing, and simulated armÐleg climbing all provide excel- produces some improvements in poorly conditioned people, lent overload for the aerobic system.20,121,216 Based on the but 20- to 30-minute sessions achieve more optimal results if specificity concept, the magnitude of training improvement intensity achieves at least the minimum threshold. varies considerably depending on training and testing mode. As for training volume, more time devoted to workouts Individuals trained on a bicycle show greater improvement does not necessarily translate to greater improvements, partic- when tested on a bicycle than on a treadmill.150 Likewise, in- ularly among active individuals. For collegiate swimmers, dividuals who train by swimming or arm cranking show the one group trained for 1.5 hours daily while another group per- greatest improvement when measured during upper-body formed two 1.5-hour exercise sessions each day.33 Even when exercise.57 one group exercised at twice the daily volume, no differences in swimming power, endurance, or performance time improvements emerged between groups. AMERICAN COLLEGE OF SPORTS MEDICINE AND AMERICAN HEART Training Frequency ASSOCIATION UPDATED FITNESS Do 2- and 5-day-a-week training produce different effects if GUIDELINES AND RECOMMENDATIONS exercise duration and intensity remain constant for each train- The American College of Sports Medicine (ACSM) and ing session? Unfortunately, the precise answer remains elu- American Heart Association (AHA) have jointly published sive. Some investigators report training frequency influences guidelines for a “well-rounded training program” for adults cardiovascular improvements, while others maintain this fac- aged 18 to 65 years to update and clarify previous recommen- tor contributes considerably less than either exercise intensity dations on the types and amounts of physical activity needed by 97818_ch21.qxd 8/4/09 6:00 PM Page 476

476 Section 4 Enhancement of Energy Transfer Capacity

TABLE 21.8 • Physical Activity Recommendations by the American College of Sports Medicine and the American Heart Association for Healthy Adults Aged 18 to 65 Years 1. To promote and maintain good health, adults aged 18 to 65 yr should maintain a physically active lifestyle. 2. They should perform moderate-intensity aerobic (endurance) physical activity for a minimum of 30 min on 5 days each week or vigorous-intensity aerobic activity for a minimum of 20 min on 3 days each week. 3. Combinations of moderate- and vigorous-intensity activity can be performed to meet this recommendation. For example, a person can meet the recommendation by walking briskly for 30 min twice during the week and then jogging for 20 min on 2 other days. 4. These moderate- or vigorous-intensity activities are in addition to the light-intensity activities frequently performed during daily life (e.g., self-care, washing dishes, using light tools at a desk) or activities of very short duration (e.g., taking out trash, walking to parking lot at store or office). 5. Moderate-intensity aerobic activity, which is generally equivalent to a brisk walk and noticeably accelerates the heart rate, can be accumulated toward the 30-min minimum by performing bouts each lasting 10 or more minutes. 6. Vigorous-intensity activity is exemplified by jogging and causes rapid breathing and a substantial increase in heart rate. 7. In addition, at least twice each week adults will benefit by performing activities using the major muscles of the body that maintain or increase muscular strength and endurance. 8. Because of the dose-response relation between physical activity and health, persons who wish to further improve their personal fitness, reduce their risk for chronic diseases and disabilities, or prevent unhealthy weight gain will likely benefit by exceeding the minimum recommended amount of physical activity.

From Haskell WL, et al. Physical activity and public health: Updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc 2007;39:1423.

6,73 health adults to improve and maintain health (TABLE 21.8). that each physiologic and metabolic system responds in a For example, a combined program of aerobic training and re- unique and different way. sistance training increases muscular strength and aerobic The data in TABLE 21.10 complement those in Figure 21.21; power, decreases body fat, and increases basal metabolic rate. they reveal the rapidity of maximum cardiovascular adapta- In contrast, singular-focus programs of either resistance only or tions to aerobic exercise training. Five young adult men and aerobic training only produce singularly larger but more limited five women trained daily for 10 consecutive days. Exerciseи 40,160 overall effects. For older adults (TABLE 21.9), emphasis is consisted of 1 hour of иcycling—10 minutes at 65% VO2peak, also placed on exercises to increase joint flexibility and improve 25 minutes at 75% VO2peak and theи last 25 minutes of 143 balance so as to reduce the risk of injury from slips and falls. repeat five 3-minute intervals at 95% VO2peak followed by a 2-minute recovery. This relativelyи brief 10-day training period induced a 10% increase in VO2peak and a 12% increase in INTEGRATIVE QUESTION cardiac output, 15% increase in stroke volume, and a slight Explain what factors account for differences in decrease in peak exercise heart rate. Resting plasma volume responsiveness of individuals to the same increased nearly 9% during the 10 days of training and corre- exercise-training program. lated with the increases in exercise cardiac output and stroke volume. This means that cardiovascular adaptations occur with short-term exercise training in young men and women. The stroke volume increases during exercise reflect the com- HOW LONG BEFORE bined effects of increased left ventricular end-diastolic dimension (preload in accordance with the Frank-Starling IMPROVEMENTS OCCUR? mechanism) and increased systolic ejection. Improvements in aerobic fitness occur within several weeks. FиIGURE 21.21 shows absolute and percentage improvements in Trainability and Genes VO2max for subjects who trained 6 days a week for 10 weeks. Training consisted of stationary cycling for 30 minutes 3 days A strenuous exercise program enhances a person’s level of fit- a week combined with running for up to 40 minutes on alter- ness regardless of genetic background. However, the limits nate days. The continuous week-to-week improvement in aer- for developing fitness capacity appear to link closely to natu- obic capacity indicates that training improvement in ral endowment. Of two individuals in the same exercise pro- previously sedentary persons occurs rapidly and steadily. gram, one might show 10 times more improvement than the Adaptive responses eventually level off as subjects approach other. A genotype dependency exists for much of one’s their “genetically predisposed” maximums. The exact time sensitivity in responding to maximal aerobic and anaerobic for this leveling off remains unknown, particularly for high- power training, including adaptations of most muscle intensity training. The data presented in Figure 21.15 indicate enzymes.17,39,67 Stated differently, identical twins in a pair 97818_ch21.qxd 8/4/09 6:00 PM Page 477

CHAPTER 21 Training for Anaerobic and Aerobic Power 477

TABLE 21.9 • Physical Activity Recommendations by the American College of Sports Medicine and the American Heart Association for Older Adults (Ͼ65 years) 1. To promote and maintain good health, older adults should maintain a physically active lifestyle. 2. They should perform moderate-intensity aerobic (endurance) physical activity for a minimum of 30 min on 5 days each week or vigorous-intensity aerobic activity for a minimum of 20 min on 3 days each week. Moderate-intensity aerobic activity involves a moderate level of effort relative to an individual’s aerobic fitness. On a 10-point scale, where sitting is 0 and all-out effort is 10, moderate-intensity activity is a 5 or 6 and produces noticeable increases in heart rate and breathing. On the same scale, vigorous- intensity activity is a 7 or 8 and produces large increases in heart rate and breathing. For example, given the heterogeneity of fitness levels in older adults, for some older adults a moderate-intensity walk is a slow walk, and for others it is a brisk walk. 3. Combinations of moderate- and vigorous-intensity activity can be performed to meet this recommendation. These moderate- or vigorous-intensity activities are in addition to the light-intensity activities frequently performed during daily life (e.g., self-care, washing dishes) or moderate-intensity activities lasting 10 min or less (e.g., taking out trash, walking to parking lot at store or office). 4. In addition, at least twice each week older adults should perform muscle strengthening activities using the major muscles of the body that maintain or increase muscular strength and endurance. It is recommended that 8 to 10 exercises be performed on at least two nonconsecutive days per week using the major muscle groups. To maximize strength development, a resistance (weight) should be used that allows 10 to 15 repetitions for each exercise. The level of effort for muscle-strengthening activities should be moderate to high. 5. Because of the doseÐresponse relationship between physical activities and health, older persons who wish to further improve their personal fitness, reduce their risk for chronic diseases and disabilities, or prevent unhealthy weight gain will likely benefit by exceeding the minimum recommended amount of physical activity. 6. To maintain the flexibility necessary for regular physical activity and daily life, older adults should perform activities that maintain or increase flexibility on at least 2 days each week for at least 10 min each day. 7. To reduce risk of injury from falls, community-dwelling older adults with substantial risk of falls should perform exercises that maintain or improve balance. 8. Older adults with one or more medical conditions for which physical activity is therapeutic should perform physical activity in a manner that effectives and safely treats the condition(s). 9. Older adults should have a plan for obtaining sufficient physical activity that addresses each recommended type of activity. Those with chronic conditions for which activity is therapeutic should have a single plan that integrates prevention and treatment. For older adults who are not active at recommended levels, plans should include a gradual (or stepwise) approach to increase physical activity over time. Many months of activity at less-than-recommended levels is appropriate for some older adults (e.g., those with low fitness) as they increase activity in a stepwise manner. Older adults should also be encouraged to self-monitor their physical activity on a regular basis and to reevaluate plans as their abilities improve or as their health status changes.

From Nelson ME et al. Physical activity and public health in older adults: Recommendation from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc 2006;39:1435.

TABLE 21.10 • Maximum Physiologic Responses During Peak Cycle Ergometer Exercises Before and After 10 Consecutive Days of Aerobic Training Variable Pretraining Posttraining и и Ϫ1 Ϯ Ϯ a VO2peak, L min 2.54 0.29 2.80 0.32 Cardiac output, L и minϪ1 18.3 Ϯ 1.3 20.5 Ϯ 1.7a Heart rate, b и minϪ1 189 Ϯ 2 184 Ϯ 2a Stroke volume, mL 97 Ϯ 7 112 Ϯ 9a _ и Ϫ1 Ϯ Ϯ a-vO2 diff, mL dL 13.6 0.8 13.4 0.6 Plasma volume (rest), mL 2896 Ϯ 175 3152 Ϯ 220a

From Mier CM, et al. Cardiovascular adaptations to 10 days of cycle exercise. J Appl Physiol 1997; 83:1900. aStatistically significant at the .05 level from pretraining value.

generally show a training response of similar magnitude. existed that the other twin would also be a responder; similarly, FIGURE 21.22и (A and B) indicates a clear similarity in the re- the brother of a nonresponder to exercise training generally и Ϫ1 и Ϫ1 sponse of VO2max (both mL kg min and % improvement) showed little improvement. Presence of the muscle-specific among 10 pairs of male identical twins who participated in the creatine kinase gene provides one example of the possible con- same 20-week aerobic exercise training program. If one twin tribution of genetic makeup to individual differences in respon- и 171,172 showed high responsiveness to training, a high likelihood siveness of VO2max to endurance training. 97818_ch21.qxd 8/4/09 11:16 PM Page 478

478 Section 4 Enhancement of Energy Transfer Capacity MAINTENANCE OF AEROBIC

8 FITNESS GAINS An important question concerns optimal exercise frequency, duration, and intensity to maintain aerobic improvements 6 withи training. In one study, healthy young adults increased VO2max 25% with 10 weeks of interval training by bicycling and running for 40 minutes, 6 days a week.78 They then joined 4 one of two groups that continued to exercise an additional 15 weeks at the same intensity and duration but at reduced frequency to either 4 or 2 days a week. Both groups main- 2 tained their gains in aerobic capacity despite up to two-thirds reduction in training frequency. Percentage improvement Percentage A similar study evaluated reduced training duration on 0 maintenance of improved aerobic fitness.79 Upon completion 4.5 of the same protocol outlined previously for the initial 10 weeks of training, subjects continued to maintain intensity

and frequency of training for an additional 15 weeks, but at )

–1 reduced training duration from the original 40-minute ses- 4.0 sions to eitherи 26 or 13 minutes per day. They maintained min

. almost all VO2max and performance increases despite a two- thirds reduction in training duration. Importantly, if training (L (L intensity decreased and frequency and duration remained con- 3.5

2max stant, even a one-third reduction in exercise intensity reduced и 80

VO the VO2max . Aerobic capacity improvement involves somewhat dif- 3.0 ferent training requirements than its maintenance. With intensity held constant, the frequency and duration of exercise 0 01 2345678910 required to maintain a certain level of aerobic fitness remain Training duration (weeks) considerably lower than that required to induce improvement. Inи contrast, a small decline in exercise intensity reduces VO . This indicates that exercise intensity plays a principal Figure 21.21 • Continuous improvements in V˙ O2max during 2max 10 weeks of high-intensity aerobic training. (From Hickson role in maintaining the increase in aerobic capacity achieved RC, et al. Linear increases in aerobic power induced by a through training. program of endurance exercise. J Appl Physiol 1977;42:373.)

16 40 14 35 ) Twin B r=0.74 Twin B r=0.82 –1 12 30 ) 10 25 min . 8 2max 20 -1 g

k 6 15 . (% VO Improvement Improvement 4 Twin A 10 Twin A (mL (mL 2 5 0 0 A 0246810 12 14 16 B 0 5 10 15 20 25 30 35 40 Improvement (mL · kg–1 · min–1) Improvement (% VO2max)

и _1 и _1 Figure 21.22 • Responsiveness of V˙ O2max (A, mL kg min ; B, % improvement) of 10 pairs of identical twins to a 20-week program of aerobic exercise training. r, Pearson product-moment correlation coefficient. Each of the 10 colored data points represents a twin pair. (From Bouchard C. Heredity, fitness, and health. In: Bouchard C, et al., eds. Physical activity, fitness, and health, Champaign, IL: Human Kinetics, 1990.) 97818_ch21.qxd 8/4/09 6:00 PM Page 479

CHAPTER 21 Training for Anaerobic and Aerobic Power 479 и Components Other Than VO2max Anaerobic Training и Fitness components other than VO2max more readily suffer ad- Figure 21.1 shows that the capacity to perform all-out exercise verse effects of reduced exercise training volume. Well- for up to 60 seconds largely depends on ATP generated by the trained endurance athletes who normally trained 6 to 10 hours immediate and short-term anaerobic systems for energy transfer. weekly reduced weekly training to one 35-minute session 125 и over a 4-week period. VO2max remained constant during INTEGRATIVE QUESTION this period of reduced training volume. However, endurance и In what specific ways would anaerobic exercise capacity at 75% VO decreased; this performance decre- 2max training improve performance in all-out physical ment related to reduced preexercise glycogen stores and a di- activity? minished level ofи fat oxidation during exercise. A single measure such as VO2max cannot adequately evaluate all of the factors that affect exercise training and detraining adaptations. The Intramuscular High-Energy Phosphates Tapering for Peak Performance American football, weightlifting, and other brief Little improvement occurs in the aerobic systems during the sprintÐpower sport activities rely almost exclusively on en- competitive season. At best, athletes strive to prevent physio- ergy derived from the intramuscular high-energy phosphates logic and performance deterioration as the season progresses. ATP and PCr. Engaging specific muscles in repeated 5- to Before major competition, athletes often taper training inten- 10-second maximum bursts of effort overloads energy trans- sity and/or volume, believing such adjustments reduce physi- fer from this phosphagen pool. Consequently, only small ologic and psychologic stress of daily training and optimize amounts of lactate accumulate and recovery progresses rap- exercise performance. The taper period and exact alterations idly. Exercise can begin again after a 30-second rest period. in training vary by sport. A 1- to 3-week taper exponentially The use of brief, all-out exercise bursts interspersed with re- reduces training volume by 40 to 60%, while maintaining covery represents a highly specific application of interval training intensity provides the most efficient strategy to max- training to anaerobic conditioning (see p. 480). imize performance gains.16,209 Physical activities to enhance ATPÐPCr energy transfer From a physiologic perspective, a 4- to 7-day taper capacity must engage the sport-specific muscles at the move- should provide sufficient time for maximum muscle and liver ment speed and power output similar to performance of the glycogen replenishment, optimal nutritional support and sport itself. This strategy enhances metabolic capacity of restoration, alleviation of residual muscle soreness, and heal- specifically trained muscle fibers; it also facilitates recruit- ing of minor injuries. In one study of competitive runners, a ment and modulation of the neural firing sequence of appropriate motor units activated in the particular movement. 1-week taper period applied either no trainingи (rest), low- intensity running (2 to 10 km daily at 60% VO2max), or high- intensity running while reducing training volume (five 500-m Lactate-Generating Capacity repeats on day 1, decreasing one repeat each day).188 Measurements during the taper included blood volume, red To improve energy transfer capacity by the short-term blood cell mass, muscle glycogen content, muscle mitochon- lactic acid energy system, training must overload this aspect drial activity, and 1500-m race performance. Compared with of energy metabolism. rest and low-intensity exercise taper conditions, high- Training of the glycolytic short-term energy system de- intensity exercise taper produced the most benefit. An optimal mands extreme physiologic and psychologic effort. Blood taper therefore should include progressive reductions in train- lactate rises to near-peak levels with a 1-minute maximum ing volume while maintaining training intensity at a moderate- bout of exercise. The individual repeats the exercise bout after to-high level. With proper tapering, expected performance 3 to 5 minutes of recovery. Repetition of exercise causes “lac- improvement usually ranges between 0.5 and 6.0%.141 tate stacking,” which produces a higher blood lactate level Tapering does not associate with substantial changes in exercise- than just one all-out exhaustive effort. As with all training, induced oxidative stress.215 one must exercise the specific muscle groups that require enhanced anaerobic function. A backstroke swimmer trains by swimming the backstroke (or use of an appropriate swim- TRAINING METHODS bench ergometer); a cyclist should bicycle; and basketball, Performance improvements occur yearly in almost all athletic hockey, or soccer players rapidly perform various movements competitions. These advances generally relate to increased and direction changes similar to the sport requirement. opportunities for participation: Individuals with “natural en- As discussed in Chapter 7, recovery requires consider- dowment” have opportunities to participate in different sports. able time when exercise involves a large anaerobic compo- Improved nutrition and health care, better equipment, and nent. For this reason, anaerobic power training of the more systematic and scientific approaches to athletic training short-term energy system should occur at the end of the con- also contribute. The following sections present general guide- ditioning session so fatigue does not hinder ability to perform lines for effective anaerobic and aerobic exercise training. subsequent aerobic training. 97818_ch21.qxd 8/4/09 6:00 PM Page 480

480 Section 4 Enhancement of Energy Transfer Capacity Aerobic Training Relatively brief bouts of repeated exercise, as well as continuous, long-duration efforts, enhance aerobic capacity, FIGURE 21.23 indicates two important factors in formulating provided exercise reaches sufficient intensity to overload the aerobic training: aerobic system. Interval training, continuous training, and 1. Cardiovascular overload must be intense enough to fartlek training represent three common methods to improve sufficiently increase (overload) stroke volume and aerobic fitness. cardiac output. 2. Cardiovascular overload must occur from activation INTEGRATIVE QUESTION of sport-specific muscle groups to enhance local cir- What information would you need to effectively culation and the muscle’s “metabolic machinery.” improve aerobic capacity for the specific In essence, proper endurance training overloads all physical job performance requirements for components of oxygen transport and use. This consideration (1) firefighters, (2) police officers, and (3) oil embodies the specificity principle of aerobic training. Simply field workers? stated, runners must run, cyclists must bicycle, rowers must row, and swimmers must swim.

Interval Training With correct spacing of exercise and rest intervals, one can perform extraordinary amounts of intense physical activity, not normally possible if activity progressed continuously. Repeated exercise bouts (with brief rest periods or low- intensity exercise relief intervals) vary from a few seconds to several minutes or longer depending on the desired training outcome.76,103,105 As little as six sessions of brief near all-out effort interval training over a 2-week period increases skeletal muscle oxidative capacity and endurance performance.58 The interval training prescription evolves from the following four

O2 O2 O considerations: 2 Goal 1 O O 2 Develop functional 2 O 2 capacity of the 1. Intensity of exercise interval O 2 central circulation 2. Duration of exercise interval 3. Length of recovery (relief) interval 4. Number of repetitions of the exerciseÐrelief interval Consider the following example of performing a large volume of intense exercise during an interval-training work- Delivery of oxygen via red blood cells out. Few people can maintain a 4-minute-mile pace for longer than 1 minute, let alone complete a mile in 4 minutes. Release of oxygen Suppose running intervals were limited to only 10 seconds O2 to active muscle followed by a 30-second recovery. This scenario makes it rea- Goal 2 sonably easy to maintain the exerciseÐrelief intervals and Enhance aerobic Energy capacity of the complete the mile in 4 minutes of actual running. This does specific muscles not parallel a world-class performance but illustrates that a person can accomplish a considerable quantity of normally exhausting exercise given proper spacing of rest and exercise intervals. This strategy of intense training interspersed with rest intervals would apply to treadmill, stair climbing, and bicycle ergometer exercise routines performed in health clubs and training centers.

Rationale for Interval Training. Interval training has a sound basis in physiology and energy metabolism. In the example of a continuous 4-minute-mile run, anaerobic glycoly- Figure 21.23 • The two major goals of aerobic training: Goal sis generates a large portion of the energy requirement. 1, develop the capacity of the central circulation to deliver Within a minute or two, the lactate level rises precipitously oxygen; Goal 2, enhance the capacity of the active and the runner fatigues. For interval training, repeated 10-second musculature to supply and process oxygen. exercise bouts permit completion of intense exercise without 97818_ch21.qxd 8/4/09 6:00 PM Page 481

CHAPTER 21 Training for Anaerobic and Aerobic Power 481

TABLE 21.11 • Guidelines for Determining Interval-Training Exercise Rates for Running and Swimming Different Distances Interval Training Distances (yards)

Run Swim Work Rate for Each Exercise Interval or Repeat

55 15 1.5 seconds slower than best 110 25 3.0Ά times from a running (or swimming) start 220 55 5.0 for each distance 440 110 1 to 4 seconds faster than the average 440-yard run or 110-yard swim times recorded during a mile run or 440-yard swim 660Ð1320 165Ð320 3 to 4 seconds slower than the average 440-yard run or 100-yard swim times recorded during a mile run or 440-yard swim

From Fox EL, Mathews DK. Interval training. Philadelphia: WB Saunders, 1974.

appreciable lactate buildup because intramuscular high- the duration of the relief interval. The ratio 1:3 energy phosphates provide the primary energy source. generally applies to training the immediate energy sys- Minimal fatigue develops during the predominantly “alactic” tem. Thus, for a sprinter who runs 10-second intervals, exercise interval and recovery progresses rapidly. The exercise the relief interval equals about 30 seconds (3 ϫ 10 s). interval can then begin following only a brief rest. For training the short-term glycolytic energy system, In interval training, exercise intensity must activate the the relief interval averages twice the exercise interval, particular energy systems that require improvement. TABLE 21.11 or a ratio of 1:2. These specific workÐrelief ratios for provides practical guidelines to determine the appropriate ex- anaerobic training should ensure sufficient restoration ercise and recovery intervals for running and swimming dif- of intramuscular phosphates and/or sufficient lactate ferent distances. The following examples serve to illustrate: removal so the next exercise bout can continue with minimal fatigue. ¥ Exercise interval: Generally add 1.5 to 5.0 seconds to ¥ To train the long-term aerobic energy system, the the exerciser’s “best time” for training distances be- exerciseÐrelief interval ratio usually is 1:1 or 1:1.5. tween 55 and 220 yards for running and 15 and During a 60- to 90-second high-intensity exercise in- 55 yards for swimming.47 If a person can run 60 yards terval, oxygen consumption increases rapidly to a from a running start in 8 seconds, the training time for high level but remains inadequate to meet exercise each repeat equals 8 ϩ 1.5, or 9.5 seconds. For an energy requirements. The recommended relief inter- interval-training distance of 110 yards, add 3 seconds, val causes the succeeding exercise interval to begin and for a distance of 220 yards, add 5 seconds to the before complete recovery (before return to baseline best running times. This particular type of interval oxygen consumption). This ensures that cardiovascu- training applies to training the intramuscular ATPÐPCr lar and aerobic metabolic stress reach near peak energy system. levels with repeated but relatively short exercise in- ¥ Training distances of 440 yards running or 110 yards tervals. The duration of the rest interval takes on less swimming: Determine the exercise rate by subtract- importance with longer periods of intermittent exer- ing 1 to 4 seconds from the best 440-yard part of a cise because sufficient time exists for the body to ad- mile run or 110-yard part of a 440-yard swim. If a just metabolic and circulatory parameters during person runs a mile in 7 minutes (averaging 105 s per exercise. 440 yd), the interval time for each 440-yard repeat range is 104 seconds (105 Ϫ 1) to 101 seconds (105 Ϫ 4). For training intervals beyond 440 yards, INTEGRATIVE QUESTION add 3 to 4 seconds for each 440-yard portion of the A coach insists that a single exercise mode interval distance. In running an interval of 880 yards, improves aerobic capacity for all physical the 7-minute miler runs each interval at about activities requiring a high level of aerobic fitness. 216 seconds [(105 ϩ 3) ϫ 2 ϭ 216]. Give your opinion regarding the potential ¥ Relief interval: The relief interval is either passive effectiveness of single-mode exercise to produce (restÐrelief) or active (workÐrelief). A ratio of exer- generalized cross-training effects. cise duration to recovery duration usually formulates 97818_ch21.qxd 8/4/09 6:00 PM Page 482

482 Section 4 Enhancement of Energy Transfer Capacity

950 4.4 850 ) 4.0 750 –1 2max min (W) 3.6

650 . VO (L (L Peak power Peak 550 3.2 0 0 )

20 –1 60

50 16 min . 2max -1 40 12 VO kg . output (KJ) Total power Total 30 0 0 (mL (mL A 1st 2nd 3rd 4th B Pre Post Exercise bout

16 16 12 12 8 MDH 4 –1 8 –1 PFK

h h 0 . .

-1 4 -1 8 6 0 4 SDH 2 0.6 0 kg protein kg protein . 0.4 . 6 mol mol 4 HEX 0.2 CS 2 0.0 0 C Pre Post D Pre Post

Figure 21.24 • Peak power output and total power output during four successive maximum 30-second efforts (A), V˙ O2max (B), maximal enzyme activity for phosphofructokinase (PFK) and hexokinase (HEX) (C), and maximal enzyme activity for malate dehydrogenase (MDH), succinate dehydrogenase (SDH), and citrate synthase (CS) (D) before (yellow bars) and after (red bars) 7 weeks of sprint interval training. (From MacDougall JD, et al. Muscle performance and enzymatic adaptations to sprint interval training. J Appl Physiol 1998;84:2138.)

Sprint-Type Interval Training Affects Anaerobic and Continuous Training Aerobic Physiologic Systems. FIGURE 21.24 shows that relatively brief but intense sprint-type interval training increases Continuous or long, slow, distance (LSD) training in- parameters of both anaerobic and aerobic metabolic capacity. volves steady-paced, prolonged exercise at eitherи moderate or The 7-week training program for 12 young adult men con- high aerobic intensity, usually 60 to 80% VO2max. The exact sisted of 30 seconds of maximum sprint effort (Wingate pro- pace can vary, but it must minimally meet a threshold inten- tocol) interspersed with 2 to 4 minutes of recovery performed sity to ensure aerobic physiologic adaptations. Previously, we three times a week. Week 1 began with four exercise intervals outlined the method to establish the training-sensitive zone with 4 minutes recovery per interval and progressed to 10 ex- that uses HRmax (pp. 471Ð474). Continuous training that exercise intervals with a 2.5-minute recovery per exercise bout ceeds one hour has become popular among fitness enthusi- by week 7. Despite this relatively brief training stimulus in asts, including competitive endurance athletes such as which exercise duration reached only 5 minutes per session triathletes and cross-country skiers. Many elite distance run- и ners train twice daily and run 100 to 150 miles weekly to pre- during week 7, improvements occurred in VO2max, short-term power output, and maximal activity of key marker enzymes in pare for competition. the aerobic and anaerobic energy pathways. Healthy elderly Continuous exercise training (because of its submaximal persons also show positive clinical and cardiovascular adapta- nature) progresses in relative comfort. This contrasts with tions to interval training.2 the potential hazards of high-intensity interval training for 97818_ch21.qxd 8/4/09 6:00 PM Page 483

CHAPTER 21 Training for Anaerobic and Aerobic Power 483 coronary-prone individuals and the high level of motivation Two clinical forms of overtraining have been described: required for such strenuous exercise. Continuous training 1. The less common sympathetic form (basedowian ideally suits novices who wish to accumulate a large caloric for thyroid hyperfunction patterns), characterized by expenditure for weight loss. When applied to athletic training, increased sympathetic activity during rest; generally continuous training truly represents “overdistance” training, typified by hyperexcitability, restlessness, and im- with most athletes training two to five times the actual dis- paired exercise performance. This form of overtrain- tances of competitive events. ing may reflect excessive psychologic/emotional stress Continuous training allows endurance athletes to exer- that accompanies the interaction among training, cise at nearly the same intensity as actual competition. competition, and responsibilities of normal living.108 Specific motor unit recruitment depends on exercise intensity, 2. The more common parasympathetic form (addis- so continuous training may best apply to endurance athletes onoid for adrenal insufficiency patterns) character- who desire adaptations at the cellular level. In contrast, inter- ized by predominance of vagal activity during rest/ val training often places disproportionate stress on the fast- and exercise. More properly termed overreaching in twitch motor units, not slow-twitch units predominantly the early stages (within as few as 10 days), the syn- recruited in endurance competition. drome qualitatively is similar in symptoms to the full-blown parasympathetic overtraining syndrome Fartlek Training but of shorter duration. Excessive and protracted ex- Fartlek, a Swedish word meaning “speed play,” repre- ercise overload with inadequate recovery and rest sents a training method introduced to the United States in the leads to overreaching. Initially, maintaining exercise 1940s. This relatively unscientific blending of interval and performance requires greater effort; this eventually continuous training has particular application to exercise out- leads to performance deterioration in training and of-doors over natural terrain. The system uses alternate run- competition. Short-term rest intervention of a few ning at fast and slow speeds over level and hilly terrain. days up to several weeks usually restores full func- In contrast to the precise exercise-interval training pre- tion. Untreated overreaching eventually leads to the scription, fartlek training does not require systematic manipu- overtraining syndrome. lation of exercise and relief intervals. Instead, the performer Parasympathetic overtraining syndrome involves determines the training schema based on “how it feels” at the chronic fatigue during exercise workouts and recovery peri- time, similar to gauging exercise intensity based on one’s rat- ods. Associated symptoms include sustained poor exercise ing of perceived exertion (RPE). When properly applied, this performance, altered sleep patterns and appetite, frequent in- method overloads one or all of the energy systems. Fartlek fections, persistent feelings of fatigue, altered immune and re- training provides ideal general conditioning and off-season productive functions, acute and chronic alterations in training strategies, although it lacks the systematic and quan- systemic inflammatory responses, mood disturbances (anger, tified approaches of interval and continuous training. It also depression, anxiety), and general malaise and loss of interest adds freedom and variety to workouts. in high-level training. Insufficient evidence prevents proclaiming superiority of any specific training method to improve aerobic capacity and associated physiologic variables.138 Each form of training pro- Definitions of Terms Related to the 175 duces success. One can probably use the various training meth- Overtraining Syndrome ods interchangeably, particularly to modify training and achieve ¥ Overload: A planned, systematic, and progres- a more psychologically pleasing exercise or training regimen. sive increase in training to improve performance. ¥ Overreaching: Unplanned, excessive overload OVERTRAINING: TOO MUCH with inadequate rest. Poor performance is ob- OF A GOOD THING served in training and competition. Successful recovery should result from short-term (i.e., a Ten to 20% of athletes experience overtraining or “stale- few days up to 1 or 2 weeks) interventions. ness.” The overtrained condition (syndrome) represents more ¥ Overtraining syndrome: Untreated overreaching than just short-term inability to train hard or a slight dip in that produces long-term decreased performance competition-level performance. Athletes can fail to endure and impaired ability to train. Other associated and adapt to training so that normal exercise performance de- problems may require medical attention. teriorates, and they encounter increasing difficulty fully recovering from a workout.22,194,212 This takes on crucial importance for elite athletes where performance decrements FIGURE 21.25 illustrates possible interactive factors that of 1 to 3% can cause a gold medalist to fail to qualify for com- initiate the parasympathetic-type overtraining syndrome. petition. Overtraining also relates to increased incidence of Interactions among chronic neuromuscular, neuroendocrine, infections, persistent muscle soreness, and general malaise psychologic, immunologic, and metabolic overload during and loss of interest in sustaining high-level training. Injuries long-term, high-volume training (with insufficient recupera- occur more frequently in the overtrained state.213 tion) eventually alter physiologic function and the stress 97818_ch21.qxd 8/4/09 6:00 PM Page 484

484 Section 4 Enhancement of Energy Transfer Capacity

Selected Mechanisms Underlying Genesis of Overtraining Syndrome in Endurance Exercise

Inadequate Recovery

Training Load Competition

Nontraining Chronic Imbalance Stress Factors

Neuromuscular Sympathetic Metabolic Psychological Adrenal Overload System Overload Overload Overload Overload

Glycogen Amino acid depletion imbalance Decreased cortisol Altered response Decreased hypothalamic- neuromuscular pituitary function function Brain neurotransmitter Decreased imbalance ß-adrenoreceptor density ? ? Decreased intrinsic sympathetic activity

Altered immune function Peripheral fatigue

Altered mood state

Central fatigue

Altered reproductive function

Impaired Exercise Performance

Figure 21.25 • Schematic overview of the genesis of the overtraining syndrome in endurance sports requiring prolonged high- volume training. (Modified from Lehmann M, et al. Autonomic imbalance hypothesis and overtraining syndrome. Med Sci Sports Exerc 1998;30:1140.) 97818_ch21.qxd 8/4/09 6:00 PM Page 485

CHAPTER 21 Training for Anaerobic and Aerobic Power 485 dration reduce symptoms but nutrition alone cannot prevent TABLE 21.12 • The Overtraining Syndrome: the syndrome’s development.1,165,190 Symptoms of Staleness ¥ Unexplained and persistently poor performance and high EXERCISING DURING PREGNANCY fatigue ratings ¥ Prolonged recovery from typical training sessions or Estimates indicate that 40% or more of women in the United 74,227 competitive events States exercise during pregnancy. FIGURE 21.26 illustrates ¥ Disturbed mood states characterized by general fatigue, the prevalence and pattern of exercise during pregnancy apathy, depression, irritability, and loss of competitive drive among pregnant and nonpregnant women during the years ¥ Persistent feelings of soreness and stiffness in muscles and 1994, 1996, 1998, and 2000 combined. Nonpregnant women joints ¥ Elevated resting pulse and increased susceptibility to upper were more likely than pregnant women to meet the moderate respiratory infections (altered immune function) and or vigorous physical activity recommendations. For both gastrointestinal disturbances groups, walking was the most common activity (52% for ¥ Insomnia pregnant and 45% for nonpregnant). Pregnant women who ¥ Loss of appetite, weight loss, and inability to maintain proper engaged in either moderate or vigorous physical activity were body weight for competition ¥ Overuse injuries generally younger, non-Hispanic white, unmarried, more edu- cated, nonsmokers, and had higher incomes than less physically active counterparts. response to produce the overtrained state.68,123,174 Preexisting medical conditions, poor diet (e.g., inadequate carbohydrate Exercise Effects on the Mother or dehydration), environmental stress (e.g., heat, humidity, Maternal cardiovascular dynamics follow normal response altitude), and psychosocial pressures (e.g., monotonous train- patterns; moderate exercise offers no greater physiologic ing, frequent competition, personal conflicts) often exacer- stress to the mother other than the additional weight gain and bate training demands and increase the risk of developing the possible encumbrance of fetal tissue. Pregnant women overtraining syndrome. showed similar capacity as postpartum women to perform Significant effects of overtraining include the following: и 40 minutes of cycling at 70 to 75% VO2max. The physiologic 1. Functional impairments in the hypothalamoÐ responses to this weight-supported exercise remained largely 117 pituitaryÐgonadal and adrenal axes and sympathetic independent of gestation. Pregnancy does not compromise Ϫ1 118 neuroendocrine system reflected by depressed uri- the absolute value for aerobic capacity (L и min ). The in- nary excretion of norepinephrine and a desensitiza- crease in maternal body mass and changes in coordination ␤ 50,108,207 and balance as pregnancy progresses adversely affect exercise tion of the 2-adrenergic system. 2. Exercise-induced increases in adrenocorticotropic economy; this adds to exercise effort with weight-bearing ex- hormone and growth hormone and decreases in corti- ercise. Pregnancy, particularly in the last trimester, also in- sol and insulin levels.212 creases pulmonary ventilation at a given submaximal exercise level.117 The direct stimulating effects of progesterone and in- In some ways, the syndrome reflects the body’s attempt creased chemoreceptor sensitivity to carbon dioxide con- to provide the athlete with an appropriate recuperative period tribute to maternal exercise “hyperventilation.”226 Regular, from intense training and competition. Despite the highly in- moderate exercise during the second and third trimesters re- dividualized specific symptoms of overtraining, those out- duces submaximal ventilatory demands and RPE.147 This lined in TABLE 21.12 are most common. No simple method training adaptation increases the mother’s ventilatory reserve diagnoses overtraining in its earliest stages.52,71 The best indi- and possibly inhibits exertional dyspnea. TABLE 21.13 summa- cations include deterioration in physical performance, alter- rizes the important maternal metabolic and cardiorespiratory ations in mood, a relatively high cortisol/cortisone ratio, and adaptations during pregnancy. possibly decreased nocturnal heart rate variability.7,154,187 Conditions that cause some athletes to thrive in training initi- Exercise Effects on the Fetus ate an overtraining response in others. Generally, rest can re- lieve the symptoms; if not, they will persist, so complete Performing exercise during pregnancy requires adherence to recovery often requires weeks or months. No reliable method prudent guidelines and recommendations.4 Epidemiologic ev- can determine the point of complete recovery from the over- idence indicates that exercise during pregnancy does not in- training syndrome, but most athletes know when they can crease risk of fetal deaths or low birth weights, and may successfully return to competition. significantly reduce the risk of preterm births.91,184 In fact, a Coaches must allow adequate recuperation during the moderate program of weight-bearing exercise or recreational most intense training cycles or when an athlete attempts to reactivity early in pregnancy through term enhances fetoplacen- gain peak form following a protracted layoff. Nutrition be- tal growth and reduces preeclampsia risk.29,177 A study of comes particularly important during intense training; special middle-class women evaluated the effects of daily low-to- emphasis placed on glycogen replenishment (sufficient recov- moderate exercise (Ͻ1000 kCal и wkϪ1), more intense exer- ery time plus high levels of dietary carbohydrate) and rehy- cise (Ͼ1000 kCal и wkϪ1), or no exercise on timely delivery 97818_ch21.qxd 8/4/09 6:00 PM Page 486

486 Section 4 Enhancement of Energy Transfer Capacity

Home exercise

Weightlifting

Bicycling

Running/ jogging

Gardening

Swimming

Type of physical activity Type Aerobics Figure 21.26 • Common Other physical activities among pregnant and nonpregnant Walking women (1994, 1996, 1998, and 2000 data combined). (From 0 10 20 30 40 50 60 Petersen AM, et al. Correlates of Percentage of women exercising physical activity among pregnant women in the United States. Pregnant Non-pregnant Med Sci Sports Exerc 2005;37:1748.)

Potential exercise risks of intense maternal exercise that TABLE 21.13 • Important Metabolic and could alter fetal growth and development include: Cardiorespiratory ¥ Reduced placental blood flow and accompanying Adaptations During fetal hypoxia Pregnancy ¥ Fetal hyperthermia ¥ Blood volume increases 40 to 50%; hemodilution reduces ¥ Reduced fetal glucose supply hemoglobin concentration ¥ Increase in blood volume dilates the left ventricle Any factor that might temporarily compromise fetal ¥ Slight increase in oxygen consumption during rest and blood supply raises concern in counseling pregnant women submaximal, weight-supported exercise such as stationary about exercise. cycling Neonates born to exercising mothers exhibit a neurobe- ¥ Substantial increase in oxygen consumption during weight- bearing exercise such as walking and running havioral profile as early as the fifth day after birth, earlier than 28 ¥ Increased heartи rate during rest and submaximal exercise neonates from more sedentary counterparts. Exercising и Ϫ1 ¥ No change in VO2max (L min ) mothers either ran, performed aerobics, swam, or used stair- ¥ Increased ventilatory response—largely progesterone climbing exercises at least three times weekly for more than induced—during rest and submaximal exercise 20 minutes at 55% of aerobic capacity or above. The women in ¥ Possible magnified hypoglycemic response during exercise, especially late in pregnancy the control group led active lives that did not include regular, ¥ Possible depressed sympathetic nervous system response to sustained exercise. FIGURE 21.27 shows data for five behavioral exercise in late gestation clusters of the Brazelton Neonatal Assessment Scales for the offspring of 34 women who exercised regularly and 31 seden- Modified from Wolfe LA, et al. Maternal exercise, fetal well-being and tary women. No significant differences emerged between pregnancy outcome. Exerc Sport Sci Rev 1994;22:145. neonates born to exercising women and sedentary controls for clusters of factors to assess motor organization, autonomic and the safety and potential benefits of regular exercise dur- stability, and range of state behaviors. Neonates born to exer- ing pregnancy.74 No association emerged between low-to-mod- cising women scored higher in orientation behavior and abil- erate exercise and gestation length. A positive finding ity to regulate state (i.e., more alert and interested in the indicated that higher volume weekly exercise lowered rather surroundings and less demanding of their mothers). Although than raised the risk of preterm birth; among births after the the inset table indicates that axial length and head circumfer- projected term, women who performed more intense exercise ence remained similar between groups, the offspring of the delivered faster than nonexercisers. exercising women were lighter and leaner than offspring 97818_ch21.qxd 8/4/09 6:00 PM Page 487

CHAPTER 21 Training for Anaerobic and Aerobic Power 487 or fetal health,9,92,124 more conservative, prudent recommendations apply during a normal pregnancy. Thirty to 40 min- 10 utes of moderate aerobic exercise for a previously active, healthy, low-risk woman during an uncomplicated preg- 8 nancy does not compromise fetal oxygen supply or Exercise * acidÐbase status, induce heart rate signs of fetal distress, or Control 36,117,195 6 produce other adverse effects to mother or fetus. * Performed on a regular basis, such exercise maintains cardiovascular fitness and promotes a training ef- 4 fect.53,156,161,162 Hormonal action via the sympathetic nervous system during strenuous exercise probably diverts some 2 blood from the uterus and visceral organs for preferential Brazelton dimensional scores Brazelton distribution to active muscles. This could pose a hazard to a fetus with restricted placental blood flow. The accompany- 0 Orientation Range of Motor Autonomic State behavioral organization stability organization ing “In a Practical Sense” on page 488 outlines guidelines states for formulating an exercise prescription during pregnancy. This prudent approach dictates that a pregnant woman (in consultation with her health care provider) should Statistical exercise in moderation, especially if the pregnancy is at all Characteristic Exercise Control significance compromised. In addition, exercise late in pregnancy can Birth weight (kg) 3.44 3.64 yes magnify the normal maternal hypoglycemic response by in- Length (cm) 51.1 51.2 no Body fat (%) 9.7 13.1 yes creasing glucose consumption by maternal skeletal muscle; Head circumference (cm) 34.6 34.7 no in the extreme, this response could adversely affect fetal *Exercise significantly different than control 14,27 Values are means glucose supply. Pregnant women should avoid supine exercise, contact Figure 21.27 • Behavioral constellation scores of neonates in sports, high-altitude exertion, hot tub immersion, and scuba exercise and nonexercise control groups on Brazelton diving. A decrease in uterine blood flow or elevation in mater- Neonatal Behavioral Assessment Scales. Numbers preceding nal core temperature with extended-duration exercise during each set of vertical bars represent an optimum score for each environmental heat stress could compromise heat dissipation constellation; asterisks indicate statistical significance at the 130 .01 level. Insert table presents neonatal morphometric values. from the fetus through the placenta. Hyperthermia nega- (From Clapp JF III, et al. Neonatal behavioral profile of the tively affects fetal development (e.g., increased risk of neural 134 offspring of women who continue to exercise regularly tube defect), particularly in the first trimester, so women throughout pregnancy. Am J Obstet Gynecol 1999;180:91. should exercise during warm weather in the cool part of the day for shorter intervals while maintaining regular fluid intake. Within this framework, aquatic exercise serves as an ideal form of maternal exercise. Current fitness level and previous physical activity pat- from the control group. The findings support the concept terns should guide a woman’s exercise behavior throughout that continuing regular exercise throughout pregnancy an uncomplicated pregnancy and postpartum. Regular aero- modifies neonatal behavior by positively affecting early bic exercise during pregnancy plays an important role to neurodevelopment. maintain functional capacity and general well-being. It also optimizes overall weight gain during the later stages of preg- INTEGRATIVE QUESTION nancy27 and may reduce risk for cesarean delivery in women What weight control advantage during pregnancy who have never borne children.23 Controversy remains about would a daily walking program offer compared whether (1) extremes of maternal exercise benefit either with stationary cycling if each program remained mother or fetus or (2) whether exercise during pregnancy at the same initial exercise level (i.e., constant benefits labor, delivery, birth weight, and general out- walking speed or cycling power output), come.13,157 Beginning regular exercise 6 to 8 weeks postpar- frequency, and duration? tum produces no deleterious effect on volume or composition of lactation and improves aerobic fitness without impairing immune function.36,116,120 Any fitness and strength declines in the early postpartum period relative to prepregnancy per- Current Opinion Regarding Physical formance generally return by 27 weeks after delivery.210 Activity and Pregnancy Combining moderate exercise with a reduced energy intake of about 500 kCal a day allows overweight lactating women Despite examples of extreme physical activity for well- to safely lose 0.5 kg per week without adversely affecting trained women without apparent negative affect on maternal infant growth.119 97818_ch21.qxd 8/4/09 6:00 PM Page 488

488 Section 4 Enhancement of Energy Transfer Capacity

IN A PRACTICAL SENSE Exercise Prescription During Pregnancy

Pregnancy alters normal physiology, necessitating some modifica- WHEN TO STOP EXERCISE AND tion in exercise prescription. Pregnant women should consult their SEEK MEDICAL ADVICE physician before initiating an exercise program (or modifying an Discontinue exercise immediately under the following conditions: existing program) to rule out possible complications. This pertains ¥ Any signs of vaginal bleeding particularly to women of low fitness status and little exercise experi- Any gush of fluid from the vagina (premature rupture of ence prior to pregnancy. ¥ Exercise during pregnancy should heighten awareness about membranes) heat dissipation, adequate caloric and nutrient intake, and knowing ¥ Sudden swelling of ankles, hands, or face when to reduce exercise intensity. For a normal, uncomplicated ¥ Persistent, severe headaches and/or disturbances in vision; pregnancy, light-to-moderate exercise does not negatively affect unexplained lightheadedness or dizziness fetal development; the benefits of properly prescribed regular exer- ¥ Elevated pulse rate or blood pressure that does not rapidly cise during pregnancy generally outweigh potential risks. return to normal following exercise EXERCISE GUIDELINES ¥ Excessive fatigue, palpitations, or chest pain Exercise mode: Avoid exercise in the supine position, particularly ¥ Persistent uterine contractions (more than 6 to 8 per h) after the first trimester. Supine exercise impairs venous return (mass ¥ Unexplained or unusual abdominal pain of the fetus compresses inferior vena cava), which could affect car- ¥ Insufficient weight gain (Ͻ1.0 kg per month during the last two diac output and uterine blood flow. Non–weight-bearing exercise trimesters) (e.g., cycling, swimming) minimizes the effect of gravity and the added weight associated with fetal development. Low-impact, Contraindications to exercise during pregnancy: weight-bearing exercise in moderation should not pose a risk. ¥ Pregnancy-induced hypertension ¥ History of two or more spontaneous abortions Exercise frequency: Exercise 3 days a week, emphasizing continuous, steady-rate effort. Reduce the intensity of more ¥ Preterm rupture of membranes frequent exercise. ¥ Preterm labor during the prior or current pregnancy Exercise duration: Exercise 30 to 40 minutes, depending on how ¥ Incompetent cervix the person feels. ¥ Excessive alcohol intake Exercise intensity: Pregnancy alters the relationship between ¥ Persistent second to third trimester bleeding heart rate and oxygen consumption, making it difficult to ¥ History of premature labor establish guidelines from heart rate. An effective alternative Intrauterine growth retardation establishes exercise intensity based on RPE, which should range ¥ between 11 (“fairly light”) to 13 (“somewhat hard”). ¥ Anemia Rate of progression: Perform exercise on a regular basis; moderate ¥ Type 1 diabetes aerobic exercise maintains cardiovascular fitness and often ¥ Significant obesity produces a small training effect. Most women should not strive ¥ Multiple pregnancy to induce training effects, but rather maintain cardiorespiratory ¥ Smoking fitness, muscle mass, and physician-recommended weight gain. The combined effects of pregnancy per se and regular exercise From Exercise during pregnancy: Current comment from the American College of Sports Medicine, August 2000. www.Americanpregnancyhealth/ often produce improved fitness after delivery. exerciseguidelines.html

Summary enzymes. Adaptations usually accompany concomitant increases in maximal exercise performance. 1. Physical activities generally classify by the specific 5. Aerobic training adaptations increase mitochondrial energy transfer system predominantly activated. An size and number, quantity of aerobic enzymes, mus- effective exercise program trains the appropriate cle capillarization, and fat and carbohydrate oxida- energy system(s) to improve a desired physiologic tion. These improvements contribute to enhanced function or performance goal. aerobic ATP production. 2. Physical conditioning based on sound principles 6. A linear relationship exists between heart rate and optimizes improvements. The four primary training oxygen consumption from light to moderately in- principles include overload, specificity, individual tense exercise in trained and untrained individuals. differences, and reversibility. Improved stroke volume with aerobic training shifts 3. Exercise training initiates cellular adaptations and this line to the right to decrease heart rate at any sub- gross physiologic changes that enhance functional maximal exercise level. capacity and exercise performance. 7. Aerobic training induces functional and dimensional 4. Anaerobic training increases resting levels of intra- changes in the cardiovascular system to decrease muscular anaerobic substrates and key glycolytic resting and submaximal exercise heart rate, enhance 97818_ch21.qxd 8/4/09 6:00 PM Page 489

CHAPTER 21 Training for Anaerobic and Aerobic Power 489 stroke volume and cardiac output, and expand the to improve it. Even small decreases in exercise inten- _ и a-vO2 difference. sity reduce VO2max. 8. Cardiac hypertrophy represents a fundamental bio- 16. Interval, continuous, and fartlek training improve logic adaptation to increased myocardial workload the capacity of the different energy transfer systems. imposed by exercise training. Cardiac enlargement Interval training most effectively improves the with endurance training increases left ventricular immediate and short-term anaerobic energy volume and enhances stroke volume. systems. 9. Structural and dimensional changes in the left ventri- 17. Aerobic training must overload both cardiovascular cle vary with exercise training modes. Regular exer- function and metabolic capacity of specific muscles. cise does not harm normal cardiac function. Peripheral adaptations in trained muscle profoundly 10. Exercise intensity is the most crucial factor that enhance endurance performance. affects the magnitude of training improvements; 18. Prolonged and intense endurance training can precip- other factors include initial fitness level, frequency, itate the syndrome of overtraining or staleness, with exercise duration, and training mode. associated alterations in neuroendocrine and immune 11. Training intensity can be applied on either an ab- functions. The syndrome includes chronic fatigue, solute basis for exercise load or relative to a person’s poor exercise performance, frequent infections, and physiologic response. The most practical approach general loss of interest in training. Symptoms gener- sets exercise intensity to a percentage of HRmax. ally persist until the athlete relinquishes training, Training levels between 60 and 90% HRmax induce possibly for several days to months. meaningful changes in aerobic fitness. 19. At least 40% of American women exercise during 12. Training duration and intensity interact to affect the pregnancy, with walking the most common form of training response. Generally, 30-minute exercise ses- exercise (42%) followed by swimming (12%) and sions are practical and effective. Extending duration aerobics (12%). compensates for reduced exercise intensity. 20. The most serious potential exercise risks during 13. Two to 3 days a week represents the minimum pregnancy include reduced placental blood flow and frequency for aerobic training. Optimal training fre- accompanying fetal hypoxia, fetal hyperthermia, and quency remains undetermined. reduced fetal glucose supply. 14. Similar aerobic improvements occur when intensity, 21. For previously active, healthy women, moderate duration, and frequency remain constant, regardless aerobic exercise does not compromise fetal oxygen of whether exercise mode when training involves supply. large muscle groups, and the evaluation process remains mode specific. 15. Training frequency and duration to maintain im- References are available online at http://thepoint.lww.com/mkk7e. proved aerobic fitness are lower than those required 97818_ch22.qxd 8/19/09 4:00 PM Page 490

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger

CHAPTER OBJECTIVES

➤ Describe the following five methods to assess ➤ Summarize the main research findings on optimal muscular strength: (1) cable tensiometry, (2) dy- number of sets and repetitions, and frequency namometry, (3) one-repetition maximum (1-RM), and relative intensity of progressive-resistance (4) computer-assisted isokinetic dynamometry training ➤ Outline a procedure to assess 1-RM for trained ➤ Outline the model for strength-training and untrained individuals periodization ➤ Describe how to ensure test standardization and ➤ Discuss specificity of the strength-training re- fairness to evaluate muscular strength sponse related to sports and occupational tasks ➤ Compare absolute and relative upper- and lower- ➤ Differentiate between resistance training goals of body muscular strength in men and women competitive athletes and untrained middle-aged and elderly persons ➤ Describe allometric scaling to “equalize” individuals when comparing physical and exercise per- ➤ Respond to the question: Which is better for formance characteristics strength improvement—progressive resistance weight training, isometric training, or isokinetic ➤ Define concentric, eccentric, and isometric mus- training? cle actions and give examples of each ➤ Describe advantages and disadvantages of ➤ Discuss the advisability of resistance training for plyometric training for power athletes children and adolescents

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CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 491

➤ Describe how “psychologic” factors and “muscu- ➤ Discuss whether specific resistance training can lar” factors influence maximum strength capacity “shape” a muscle’s appearance and training responsiveness ➤ Review (1) the type of exercise most frequently ➤ List physiologic adaptations with chronic resist- associated with delayed-onset muscle soreness ance training (DOMS), (2) the best way to minimize DOMS when initiating training, and (3) significant ➤ Summarize current opinion concerning resistance cellular alterations with DOMS training’s effect on muscle fiber type and number ➤ Explain “core strength” development and its role ➤ Outline a circuit resistance training program for in physical performance middle-aged men and women to improve muscular strength and aerobic fitness

In the sections that follow, we explore the rationale that Part 1 ¥ STRENGTH MEASUREMENT underlies resistance training and physiologic adaptations AND RESISTANCE TRAINING when training muscles to become larger and stronger. The discussion centers on different methods to measure muscular Weightlifting in America in the early 1840s became a spec- strength, gender differences in strength, and resistance-training tator sport practiced by “strongmen” who showcased their programs to increase muscle strength (including a discussion prowess in traveling carnivals and sideshows. As pointed of “core” strength) and power. out in the text’s “Introduction: A View of the Past,” the military evaluated the strength of conscripts during the Civil War; strength measurements also provided the basis for routine fitness assessments in the prototype college and university physical education programs. An 1897 meeting of College Gymnasium Directors (Dr. D. A. Sargent, committee chair from Harvard University) established strength contests for college undergraduates to determine overall body strength and the college’s “strongest man.” Measures included back, leg, arm, and chest strength evaluated with several of the devices depicted in Figure 9 of the “Introduction” (see p. xlvii). Harvard, Columbia, Amherst, University of Minnesota, and Dickinson were the first five colleges to rank in the 1898Ð1899 competitions. By the mid-1900s, physical culture specialists, circus performers, bodybuilders, competitive weightlifters, field event athletes, and wrestlers trained predominantly using “weightlifting” exercises. Most other athletes refrained from lifting weights for fear such training would slow them and increase muscle size to the point where they would lose joint flexibility and become musclebound. Subsequent research in the late 1950s and early 1960s dispelled this myth Left. Early 1890s pose of strongman Eugene Sandow that muscle-strengthening exercises reduced speed or range (Frederick Mueller), billed by showman Florenz Ziegfeld as of joint motion. Instead, the opposite usually occurred; “The Most Perfect Man.” Sandow helped to design a physical fitness training program for the British military, inspiring a elite weightlifters, bodybuilders, and “muscle men” had future generation of bodybuilders. Right. John Grimek, exceptional joint flexibility without limitations in general member of the United States 1936 Olympic weightlifting limb movement speed. For untrained healthy individuals, team, two-time Mr. America (1940, 1941), 1948 Mr. heavy-resistance exercises increased speed and power Universe, and undefeated in bodybuilding competition. of muscular effort without impairing subsequent sports Recognized as the “best-built human” of the first half of the performance. 20th century. 97818_ch22.qxd 8/4/09 4:44 PM Page 492

492 Section 4 Enhancement of Energy Transfer Capacity Dynamometry

FIGURE 22.1B and C illustrate hand-grip and leg and back-lift dynamometers for static strength measurement based on the compression principle. An external force applied to the dynamometer compresses a steel spring and moves a pointer. The force required to move the pointer a given distance determines the external force applied to the dynamometer.

One-Repetition Maximum A dynamic procedure for measuring muscular strength applies the one-repetition maximum (1-RM) method. 1-RM refers to the maximum amount of weight lifted one time using proper form during a standard weightlifting exercise. To assess 1-RM for any muscle group, the tester makes a reasonable guess at an initial weight close to, but below, the person’s maximum lifting capacity. Weight is progressively added to the exercise device on subsequent attempts until the person reaches maximum lift capacity. The weight increments usually range between 1 and 5 kg depending on the muscle group evaluated. Rest intervals of 1 to 5 minutes usually provide sufficient recuperation before attempting a lift at the next heavier weight.

Estimate the 1-RM Late 1890s strength equipment advertised for home gym use. By the mid-1850s, rowing machines and strengthening Impracticality and/or potential risk in performing 1-RM devices became commonplace, eventually leading to studies with preadolescents, the elderly, hypertensives, cardiac of their effectiveness in American colleges (Harvard and patients, and other special populations requires an estimate Amherst) in the 1890s. 1-RM from submaximal effort. We present equations below for untrained and resistance-trained young adults. Different equations are necessary because resistance training alters MEASUREMENT OF MUSCLE STRENGTH the relationship between a submaximal performance One of the following four methods commonly assesses mus- (7- to 10-RM) and maximal lift capacity (1-RM). Generally, cle strength, or, more precisely, maximum force or tension the weight that one can lift for 7- to 10-RM represents about output generated by a single muscle or related muscle groups: 68% of the 1-RM score for the untrained person and 79% of the new 1-RM after training.30 1. Tensiometry 2. Dynamometry Untrained: 3. One-repetition maximum 1-RM (kg) ϭ 1.554 ϫ 7- to 10-RM weight (kg) Ϫ 5.181 4. Computer-assisted force and power output determinations Trained: 1-RM (kg) ϭ 1.172 ϫ 7- to 10-RM weight (kg) ϩ 7.704 Cable Tensiometry For example, estimate 1-RM bench press score for a trained person whose 10-RM bench press equals 70 kg as follows: FIGURE 22.1A shows a cable tensiometer for measuring knee extension muscle force. Increasing the force on the cable depresses 1-RM (kg) ϭ 1.172 ϫ 70 kg ϩ 7.704 the riser over which the cable passes. This deflects the pointer ϭ and indicates the subject’s strength score. The instrument meas- 89.7 kg ures muscle force in a static (isometric) muscle action that elicits little or no change in the muscle’s external length. The Computer-Assisted, Electromechanical, tensiometer (lightweight, portable, and easy to use) provides the advantage of versatility for recording force measurements at vir- and Isokinetic Methods tually all angles about a specific joint’s range of motion (ROM). Microprocessor technology rapidly quantifies forces, Standardized cable-tension strength-test batteries can assess torques, accelerations, and velocities of body segments in static force capacity of all major muscle groups. numerous movement patterns. Force platforms measure the 97818_ch22.qxd 8/4/09 4:44 PM Page 493

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 493

90°

A Cable tensiometer B Hand-grip dynamometer C Back-leg lift dynamometer

0 450 50

400 100

lb 0

100 350 150

80 300 200

kg 30

70 250

40 60 50

Figure 22.1 • Measurement of static strength with (A) cable tensiometer, (B) hand-grip dynamometer, and (C) back–leg lift dynamometer.

external application of muscle force by a limb, as in jump- The interface of microprocessor technology with me- ing. Other electromechanical devices assess forces gener- chanical devices provides the sport and exercise scientist ated during all phases of an exercise movement (e.g., with valuable data to evaluate, test, train, and rehabilitate in- cycling) or primarily arm (supine bench press) or leg (leg dividuals. The argument in support of isokinetic strength press) movements. measurement maintains that muscle strength dynamics in- An electromechanical accommodating resistance involve considerably more than just the final outcome of 1- strument, termed an isokinetic dynamometer, contains a RM. For example, two individuals with identical 1-RM speed-controlling mechanism that accelerates to a preset, scores could exhibit dissimilar force curves throughout the constant velocity with force application. Once attaining this movement. Individual differences in force dynamics (e.g., speed, the isokinetic loading mechanism adjusts automati- time to peak tension) throughout the full ROM may reflect an cally to provide a counterforce to variations in force gener- entirely different underlying neuromuscular physiology that ated by muscle as movement continues throughout the 1-RM does not assess. FIGURE 22.2 illustrates the differences “strength curve.” Thus, maximum force (or any percentage between conventional 1-RM knee extension (top: highest of maximum effort) generates throughout the full ROM at a force score during five lifts represents only total weight preestablished velocity of limb movement. This allows lifted) and a microprocessor-controlled, isokinetic resistance training (and measurement) under a continuum from device that can produce a force curve throughout the ROM high-velocity (low-force) to low-velocity (high-force) con- (bottom: force related to movement duration). In this exam- ditions. A microprocessor within the dynamometer continu- ple with an early-generation isokinetic device, note that peak ously monitors the immediate level of applied force. An torque occurred in the early phase of movement at the most electronic integrator in series with a monitor displays the advantageous angle in the ROM; the lowest torque occurred average or peak force generated during any interval for al- at full knee extension. TABLE 22.1 lists measurement units for most instantaneous feedback about performance (e.g., various expressions of muscular performance during linear force, torque, work). and angular movements. 97818_ch22.qxd 8/4/09 4:44 PM Page 494

494 Section 4 Enhancement of Energy Transfer Capacity INTEGRATIVE QUESTION I-RM Testing 100 Explain why many resistance-trained athletes have their spotters during a free-weight bench 75 press apply external force (to make the lift more difficult) in the early phase of the lift and provide 50 assistance toward its completion.

f hi g hest I-RM 25 % o 0 Resistance-Training Equipment Categories 12345 Trials Resistance training typically uses one of four types of exercise equipment to manipulate movement speed and/or resist- Isokinetic Testing ance throughout the ROM. 400 Peak torque 1. Free weights and barbells, common weightlifting equipment that does not control for or measure speed 300 of movement of the resistance through the range of ROM 200 2. a. Isokinetic equipment that provides constant speed and variable resistance b. Isokinetic, hydraulic equipment that provides Torque (N-m) Torque 100 constant speed and variable resistance, where the individual controls movement speed 3. Cam devices and concentricÐeccentric apparatus 0 03 Time (s) where movement speed varies and resistance remains constant Figure 22.2 • Top. Conventional 1-RM testing. The heaviest Another possible type of machine, not currently avail- weight lifted constitutes the 1-RM. If 150 kg (100%) is the able, would optimize muscle force with true constant speed maximum lifted, then 150 kg equals the 1-RM. Bottom. Force and constant resistance. curve obtained during an isokinetic test performed at an Ϫ angular velocity of 30° и s 1 over a 3-second interval. Peak torque in this example equals 342 N-m. Average torque is the Strength-Testing Considerations force-time integral, or impulse divided by time. Impulse Ϫ equals 602 N-m и s 1, and average torque equals 200.7 N-m Seven important considerations exist for muscle strength test- (602 N-m Ϭ3). Work equals the product of average torque ϫ ing regardless of measurement method: distance moved (90°, or 1.57 radians). Using the data for 1. Standardize instructions prior to testing. ϫ average torque and distance, work equals 174 N-m 157 2. Ensure uniformity in duration and intensity of the radians ϭ 273 N-m, or 273 joules (J). Power is work per unit warm-up. time, or 273 J Ϭ 3.0 s ϭ 91 W.

TABLE 22.1 • International System (SI) of Units for Expressing Muscular Strength and Power During Linear and Angular Motionsa Linear Motion Angular Motion Quantity Unit Quantity Unit

Force Newton, N Torque, T Newton meter, N-m Velocity Meters per second, m и sϪ1 Velocity, v Radians per second, rad и sϪ1 Mass Kilogram, kg Moment of inertia, I or J Kilogram meters squared, kg-m2 Acceleration Meters per second squared, m и sϪ2 Acceleration, a Radians per second squared, rad и sϪ2 Displacement Meter, m Displacement, ␪ Radian, rad Time Second, s Time, t Second, s

aAppendix A, available online at http://thepoint.lww.com/mkk7e, provides additional information about SI units, including interconversions. 97818_ch22.qxd 8/4/09 4:44 PM Page 495

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 495 3. Provide adequate practice prior to testing to minimize “learning” that could compromise initial results. 100 4. Ensure consistency among subjects in the angle of limb measurement and/or body position on the test 95 device. 5. Predetermine a minimum number of trials (repeti- 90 tions) to establish a criterion strength score. For ex- "true" 1-RM ample, if administering five repetitions of a test, 85 what score represents the individual’s strength score? g e o f Is the highest score best, or should one use the aver- 80 age? In most cases, an average of several trials pro-

vides a more representative (reliable) strength or Percenta 0 power score than a single measure. 12345 6. Select test measures with high test score repro- Bench-press trials ducibility. This crucial but often overlooked aspect of testing evaluates the variability of the subject’s re- Figure 22.3 • Five repeated determinations of maximal force sponses on repeated efforts. Lack of test score con- (1-RM) for the supine bench press with an electromechanical sistency (unreliability) can mask an individual’s dynamometer. Strong verbal encouragement was provided representative performance on the measure (or on each attempt. (From F. Katch, Human Performance change in performance when evaluating strength im- Laboratory, University of Massachusetts, Amherst, MA.) provement). 7. Recognize individual differences in body size and composition when evaluating strength scores among individuals and groups. For example, consider the “fairness” of comparing ab- Learning Factors Affect Strength solute muscular strength of a 120-kg football lineman with Measurements the strength of a 62-kg distance runner. No clear-cut answer In Chapter 19, we emphasized that initial gains in mus- resolves this dilemma; in the section on “Allometric Scaling” cular strength with resistance training result largely from neu- on page 498, we present alternatives for comparing strength ral factors instead of structural changes within muscle per se. scores relative to body size. FIGURE 22.3 presents data for repetition-by-repetition performance improvements in maximal force (1-RM) at an angular velocity of 5¡ и sÐ1 during a supine bench press with a 5 s interval between maximal effort repetitions. The amount of Exercise Equipment to Overload improvement averaged 11.4% between maximal force on Skeletal Muscle attempt 1 and attempt 5 and 2.1% between the last two attempts. Strength “improvement” with repeated testing indicates the necessity for at least three attempts before maxi- Equipment mum force scores begin to stabilize or plateau. Importantly, Category Speed Resistance Example use of only one or two 1-RM attempts underestimates the (I) Variable Variable Barbells (resistance “true” 1-RM by as much as 11%. If a single 1-RM trial varies through ROM preceded a 15-week strength-training program, then any even though absolute strength gains attributable to training would include the 11% weight remains “learning” improvement simply from exercise familiariza- constant) tion, regardless of a true training effect! (II) Constant Variable Hydraulic (person controls speed) Constant Variable Computer-regulated GENDER DIFFERENCES IN (movement speed controlled by MUSCLE STRENGTH computer) Several approaches determine whether a true gender differ- (III) Variable Constant CAM-adjusted ence exists in muscle strength. These evaluations relate to equipment and (1) the muscle’s cross-sectional area, (2) an absolute basis as concentricÐeccentric apparatus total force exerted, (3) architectural characteristics (e.g., (IV) Constant Constant None available fiber pennation angle), and (4) relative strength indexed to estimates of body composition (body mass or fat-free body mass [FFM]). 97818_ch22.qxd 8/4/09 4:44 PM Page 496

496 Section 4 Enhancement of Energy Transfer Capacity Strength Related to Muscle Cross-Sectional Area 40 Human skeletal muscle regardless of gender generates a maximum of between 16 and 30 newtons (N) of force per square centimeter of muscle cross section. In the body, force-output capacity varies depending on the arrangement of the bony g ) 30 levers and muscle architecture (see Chapter 18). Applying the 2 value of 30 N as a representative force capacity per cm of g th (k muscle tissue indicates that a muscle with a cross-sectional area of 5.0 cm2 develops maximal force of 150 N. If all of the 20 body’s muscles became maximally activated simultaneously (with force applied in the same direction), the resulting force would equal 168 kN. This estimation assumes a muscle total f lexor stren

cross section of 0.56 m2. rm 10 A FIGURE 22.4A compares the absolute arm flexor strength of men and women related to the flexor muscle’s total cross- sectional area (MCSA). Clearly, individuals with the largest MCSA generate the greatest absolute force. The near-linear 0 A 0 5101520 relation between strength and muscle size indicates little dif- Cross-sectional area (cm2) ference in arm flexor strength for the same size muscle in men and women. FIGURE 22.4B further demonstrates this point 10

when expressing the strength of the men and women per unit ) area of MCSA. In addition, women and men matched for –2 8 absolute muscular strength show similar fatigability of the cm .

elbow flexor muscles during sustained low-level isometric g contraction.109 6

Absolute Muscle Strength 4

Comparisons of muscular strength on an absolute score basis Stren g th per cross- 2 (i.e., total force in lb or kg) indicate that men possess considerably greater strength than women for all muscle groups sectional area (k 0 tested. Women score about 50% lower than men for upper- B 0121416182022 body strength and about 30% lower for leg strength. This gen- Age (y) der disparity exists independent of the measuring device and generally coincides with gender-related difference in muscle Adult men Adult women Judo men mass distribution. Exceptions usually emerge for strength- trained female track-and-field athletes and bodybuilders who Figure 22.4 • A. Variability of upper-arm flexion strength have strength-trained for years. of men and women related to the flexor muscle’s total cross- sectional area. B. Strength per unit muscle cross-sectional area in males and females aged 12 to 20 years. (From Ikai M, Gender Differences in Weightlifting Fukunaga T. Calculation of muscle strength per unit cross- Championships sectional area of human muscle by means of ultrasonic measurements. Arbeitsphysiologie 1968;26:26.) A unique set of data exists on gender differences in weightlifting competitions in which men and women of identical body mass participated in the same weightlifting categories. FIGURE 22.5 displays the percentage differences in maximum weight lifted in the combined snatch and clean- 82.5-kg body mass lift only about 60% of the maximal and-jerk lifts during national championship competitions. weight lifted by similar-weight male counterparts. This rep- These comparisons do not “equate” or “adjust” performance resents a more pronounced gender difference than other scores on the basis of the well-documented gender differ- comparisons that matched male and female competitors for ence in body composition. The six body weight categories body composition, not just body mass. In such comparisons, range from 52 to 82.5 kg. The lighter-weight categories usu- it is impossible to determine what role, if any, anabolic ally produce the smallest gender difference, with the effect steroid use impacted the gender differences in various ex- most pronounced in the heavier lifters. Women of 75- and pressions of muscular strength. 97818_ch22.qxd 8/4/09 4:44 PM Page 497

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 497 would conclude the male, by 61.3%. However, the bench press score divided by body mass yields a much different conclusion. For the male, the strength ratio (114 kg ÷ 95 kg) equals 1.20; the 52 ratio for the woman is 1.17 (70 kg ÷ 60 kg), which reduces the percentage difference in bench press strength to only 2.5%! This 56 alternative result would support the argument that no differences exist in muscle “quality” between men and women; rather, the 60 observed gender difference in absolute muscle strength would 67.5 reflect differences in muscle quantity (cross- sectional area). Men and women generally do not differ signifi- h tlifting category,

body mass (kg) 75 cantly in either upper- or lower-body strength when comparisons are made applying ratios with FFM (or MCSA) as the divisor. Weig 82.5 We must emphasize that this traditional ratio adjustment may not equalize women and men on the basis of the under- 0760 08090 100 lying physiology. As with aerobic capacity (discussed in Percentage of men's lift achieved Chapter 11), a fair way to evaluate a potential gender differ- by women ence in a criterion trait such as muscular strength or aerobic capacity either (1) compares men and women who do not dif- Maximum weight lifted fer in body size variables such as body mass or FFM and who Body mass (kg) category Men Women exhibit similar training status or (2) adjusts for these variables through appropriate statistical control. These solutions pre- 52 kg 185.5 165.0 clude the need to create a ratio score because men and women 56 kg 202.5 160.0 60 kg 260.0 170.0 in essence become equalized for body size and/or body com- 67.5 kg 275.0 197.5 position. With this approach, researchers assessed five meas- 75 kg 290.0 177.5 ures of muscular strength for men and women, using 1-RM 82.5 kg 325.0 195.0 concentric (shortening) muscle actions for the bench press and squat and isokinetic dynamometry to assess maximum force during knee flexion and extension and seated shoulder press. Figure 22.5 • Difference in maximum weight lifted between FIGURE 22.6 shows that matching men and women for body men and women in the same body mass categories during a mass produced larger gender differences in the sedentary national weightlifting competition. The inset shows the absolute weight lifted for each body mass category. group (44.0% for the shoulders and 25.1% for knee flexion) than in the trained group (33.0% for the bench press and 10.7% for knee flexion). The percentage differences decreased (but were not eliminated) for both groups by matching subjects INTEGRATIVE QUESTION for FFM. The shoulder press (39.4%) and bench press (31.2%) What performance would you expect in maximum produced the largest gender differences in the sedentary group, weightlifting tests comparing (1) an average- while the corresponding differences for the trained group were sized man and average-sized woman, (2) a man 30.6% (shoulder press) and 35.4% (bench press). and woman of equivalent training history and These results differ from prior studies that used the tradi- identical body mass, and (3) a man and woman of tional ratio score approach to express the strength of women and equivalent training history and identical fat-free men. Without doubt, ratio scoring supports the argument that few body mass? gender differences exist in muscle quality, at least reflected by force output capacity. In contrast, matching men and women for body size, body composition, and training status before testing yields higher upper- and lower-body strength scores for men.187 Relative Muscle Strength In a latter study of 2061 male and 1301 female military person- Relative strength comparisons among individuals involve nel, mean lift capacity averaged 51% greater in men despite a re- creating a comparative ratio score by dividing a strength gression, ratio, or exponential mathematical adjustment in the measurement (e.g., weight lifted) by a reference measurement strength score based on interindividual differences in FFM. such as body mass, FFM, MCSA, or limb volume or girth. In general, strength ratio scores based on body mass or FFM INTEGRATIVE QUESTION considerably reduce (if not eliminate) the large absolute Based on gender-related differences in physical strength differences between genders.40 fitness components, devise a physical test that Consider the following example. A male who weighs 95 kg (1) minimizes and (2) maximizes performance bench presses 114 kg; a 60-kg woman bench presses only 70 kg differences between men and women. (62% of the man’s lift). Who is “stronger?” In absolute terms, we 97818_ch22.qxd 8/4/09 4:44 PM Page 498

498 Section 4 Enhancement of Energy Transfer Capacity between maximal grip strength and body mass in college- Men and women matched aged men (purple) and women (green). The top graphs illus- for body mass trate the simple relationship between body mass and grip 50 40 strength without adjustment for body size. A positive relation- ϭ ϭ 30 ship emerges (r 0.51 for males and r 0.33 for females). 20 The middle graphs depict the relationship with grip strength erence (%) Gender 10 indexed to body mass (i.e., strength divided by body mass in ff 0 kg). The bottom graphs illustrate the relationship between di strength and allometric scaling of body mass. The resulting Men and women matched correlations between strength and body mass with the appro- for fat-free body mass priate allometric scaling fall essentially to zero (r ϭ 0.013 for 50 40 males and 0.030 for females). This satisfies one of the basic 30 tenets of allometry—the correlation between the scaled vari- 20 able (muscular strength) and the scaling factor (body mass) 10 must equal zero. The inset table (C) presents percentile norms Gender 0

ff erence (%) for the grip strength adjusted to allometric-scaled body mass -10 0.51 di exponent (grip strength per kg ) for college-aged men and -20 Bench Shoulder Knee Knee Squat women. press press extension flexion INTEGRATIVE QUESTION Sedentary Trained You have a list of the names of young adults with their corresponding body weights. Justify your Figure 22.6 • Men and women matched for body mass selection of just two people to complete these (top) and fat-free body mass (bottom) for five measures of muscle strength. Above the zero line indicates the percentage tasks: One must push a vehicle stuck in the mud by which values for men exceed values for women. (Data while the other must move hand-over-hand on a courtesy of Keller B. The influence of body size variables on rope strung across a ravine. Hint: Consider gender differences in strength and maximum aerobic absolute and relative strength requirements of capacity. Unpublished doctoral dissertation, University of each task and association between body mass and Massachusetts, Amherst, 1989.) absolute and relative muscular strength.

Allometric Scaling TRAINING MUSCLES TO Allometric scaling represents another mathematical procedure to try to establish a proper relationship between a BECOME STRONGER body size variable (usually stature, body mass, or FFM) and A muscle strengthens when trained near its current maximal some factor of interest as muscular strength, aerobic capacity, force-generating capacity. Standard weightlifting equipment, power output, jumping height, or running speed.24,124,260 The pulleys or springs, immovable bars, resistance bands, or a va- technique provides a statistical adjustment to evaluate the riety of isokinetic and hydraulic devices provide effective relative contribution of diverse independent variables (e.g., muscle overload. Importantly, overload intensity (level of ten- gender, maturation, habitual physical activity) on иthe depend- sion placed on muscle), not the type of exercise that applies ent measure of interest (e.g., muscular strength, VO2max, pul- the overload, generally governs strength improvements. monary function). Allometric scaling, a well-accepted and Certain exercise methods lend themselves to precise and valid statistical approach, also is applied in diverse areas of systematic overload applications. Progressive-resistance the biological sciences.51,126,242,248,256,257Ð259 weight training, isometric training, and isokinetic training represent three common exercise systems to train muscles to Strength and Allometric Scaling Using Body Mass. become stronger. These systems rely on the types of muscle FIGURE 22.7 illustrates the relationship between body mass and actions illustrated in FIGURE 22.8AÐC. several different expressions of muscular strength. The top left graph (A) plots the total weight lifted versus body mass for Olympic weightlifters. Each point represents body mass Different Muscle Actions of the top weightlifters in each body mass category. Neural stimulation of a muscle causes the contractile ele- Importantly, total weightlifted and body mass do not relate ments of its fibers to shorten along the longitudinal axis. The linearly but curvilinearly. Weightlifting strength relates pro- terms isometric and static describe muscle activation without portionally to body mass raised to the exponent 0.7 (the slope observable change in muscle fiber length. A dynamic muscle of the line). The bottom six curves (B) depict the relationship action produces movement of a skeletal body part such as an 97818_ch22.qxd 8/4/09 4:44 PM Page 499

420 . -0.51 400 Super Grip Strength (kg kg BW ) 1st HW 2nd HW 380 Percentile Male Female rank (X=5.46,SD=0.79) (X=3.84,SD=0.59) 360 LHW MW 340 Mid 90 6.47 4.60 320 LW 80 6.12 4.35 70 5.87 4.15 300 60 5.66 4.00

w eig h t lifted (kg) 280 Fea 50 5.46 3.85 Ban 260 40 5.26 3.70 30 5.05 3.55 Fly Tot al 0 20 4.80 3.35 60 70 80 90 100 110 120 130 140 10 4.45 3.10 A Body mass (kg) C

80 50 45 70 40 h h 60 35

50 30 (kg) (kg) 25

rip strengt 40 rip strengt G r=0.51, p<0.01 G 20 r=0.36, p<0.05 30 15

0 0

) 0.44 ) 0.38 –1 –1

0.38 0.32

kg BM r=-0.42, p<0.05 kg BM r=-0.42, p<0.05 . . 0.32 0.26 (kg (kg h h 0.26 0.20

0.20 0.14

G rip strengt 0 G rip strengt 0

7 7.5 r=0.013, p>0.50 r=-0.03, p<0.25 ) 6 ) 6.5 h h 5.5 -0.54 5 -0.54 4.5 4 kg BM kg BM

. . 3.5

G rip strengt 3 G rip strengt

(kg (kg 2.5

0 0 B 60 80 100 120 140 160 60 80 100 120 140 160 Body mass (kg) Body mass (kg)

Males Females

Figure 22.7 • Relationship between body mass and different expressions of muscular strength. A. Total weight lifted in two events as a function of body mass of Olympic weightlifters (1980 Olympic games). Each point represents the body mass of the top six male weightlifters in each of the following weight categories: Fly, flyweight; Ban, bantamweight; Fea, featherweight; LW, lightweight; Mid, middleweight; LHW, light-heavyweight; MW, middle-heavyweight; 1st HW, 1st heavyweight; 2nd HW, 2nd heavyweight; and Super, superheavyweight. (Modified from data of Lathan and cited by Titel K, Wutscherk H. In: Komi PV, ed. Strength and power in sport. Oxford: Blackwell Scientific Publications, 1993.) B. Maximal absolute grip strength, relative grip strength, and strength scaled allometrically to body mass of 100 men and 105 women of college age. C. Percentile norms for grip strength scaled to body mass. (Data courtesy of Dr. Paul Vanderburgh, University of Dayton). 97818_ch22.qxd 8/4/09 4:44 PM Page 500

500 Section 4 Enhancement of Energy Transfer Capacity

A B C Figure 22.8 • Muscle force generated during (A) concentric (shortening), (B) eccentric (lengthening), and (C) isometric (static) muscle actions.

upper or lower limb or the trunk. Concentric and eccentric ac- muscle actions because movement occurs. This term lacks tions represent the two types of dynamic muscle actions. precision when applied to most dynamic muscle actions that involve movement; the muscle’s effective force-generating ¥ Concentric action occurs when the muscle shortens capacity continually varies as the joint angle changes and joint movement occurs as tension develops. throughout the ROM. Figure 22.8A illustrates a concentric action when raising a dumbbell from the extended to the flexed elbow position. Resistance Training ¥ Eccentric action occurs when external resistance ex- The most popular form of resistance training involves lifting ceeds muscle force and the muscle lengthens while and lowering an external weight. Through appropriate and developing tension (Fig. 22.8B). The weight slowly progressive manipulation of training volume, intensity, and lowers against the force of gravity. The muscle fibers frequency to optimize dose response, this method selectively (more specifically the sarcomeres) of the upper-arm strengthens specific muscles to overcome a fixed initial or muscles lengthen in an eccentric action to prevent the changing resistance.137,209 This resistance typically takes the weight from crashing to the surface. In weight lifting, form of a barbell, dumbbell, or weight plates on a pulley- or muscles frequently act eccentrically as the weight cam-type machine. As with cardiovascular training, muscular slowly returns to the starting position to begin the strength improvements vary inversely on a continuum with next concentric (shortening) action. Eccentric muscle initial training status. Generally, improvements average 40% action during this “recovery” phase adds to the total for the untrained, 20% in the moderately trained, 15% in the work and effectiveness of the exercise repetition. trained, 10% in the advanced, and 2% in elite athletes who ¥ Isometric action occurs when a muscle generates achieve a high level of competitive success.4 force and attempts to shorten but cannot overcome the external resistance (Fig. 22.8C). From a physics standpoint, this type of muscle action does not pro- Progressive Resistance Exercise duce external work. An isometric (static) action can Progressive resistance exercise (PRE) provides a practical generate considerable force despite the lack of notice- application of the overload principle and forms the basis of able lengthening or shortening of muscle sarcomeres most resistance-training programs. Physical therapists in a re- and subsequent joint movement. habilitation hospital in the late 1940s and early 1950s devised The term isotonic, derived from the Greek word isotonos weight-training regimens to improve the strength of previ- (iso meaning “the same” or “equal,” tonos meaning “tension” ously injured limbs of soldiers returning from WWII (see or “strain”), commonly refers to concentric and eccentric “Focus on Research,” p. 501). The procedure involved three 97818_ch22.qxd 8/4/09 4:44 PM Page 501

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 501

FOCUS ON RESEARCH Develop Strength by Increasing Load, Not Repetitions

DeLorme TL. Restoration of muscle power by heavy- patient. Sudden motions should be avoided, and a momen- resistance exercises. J Bone Joint Surg 1945;27:645. tary pause at the end of each repetition was advocated.” Weekly 1-RM measurement provided the basis for pro- ➤ The accepted principle for muscle rehabilitation from gressively adjusting the load to maintain the 10-RM train- injury prior to DeLorme’s classic research involved lowing level. The figure illustrates strength improvement in resistance, high-repetition exercises called endurance- one patient undergoing rehabilitation from a femur frac- building exercises. Examples include stationary cycling, ture. After 36 days, note the 8% gain in thigh girth (1.8 in) stair climbing, and repetitively lifting light sandbags or and the 40-pound (200%) increase in quadriceps muscle weights with the aid of pulleys. The prevailing approach strength. to restoring atrophied, weak, or “neglected” muscles re- The DeLorme paper represented the first in the mod- lied on developing muscular endurance, not muscular ern strength-training literature to advocate the concept of strength and power. DeLorme challenged conventional training specificity. DeLorme argued that power-building wisdom by advocating heavy-resistance exercise. He rea- and endurance exercises “were two entirely different soned that proportionality existed between the load resist- types, each one producing its own results, and each being ing the muscle action and the rate and extent of muscle incapable of producing the results obtained by the other.” hypertrophy. DeLorme predicted that an inactive or in- More than 65 years of subsequent research has validated jured person’s strength would return to normal levels the specificity concept for strength improvement, includ- faster with heavier resistance exercise than lighter resist- ing almost every claim made by DeLorme about PRE’s ance exercise. beneficial effects. Based on observations of 300 patients, most of whom required lower-extremity rehabilitation, DeLorme developed a new training system named progressive resistance exercise (PRE). Within the PRE system, he introduced the concepts of one-repetition maximum 2.50 100 (1-RM) strength and 10-RM strength for (1) setting ini- 2.25 90 tial overload and adjusting increasing resistance, (2) es- 1-RM 2.00 80 tablishing maximal sets and repetitions, and (3) applying Circumference the concept of muscle-training specificity. For muscle re- 1.75 70 habilitation, DeLorme recommended that patients accumulate 70 to 100 repetitions of an exercise using 7 to 1.50 60 10 sets with a maximum of 10 repetitions per set. Initially, 1.25 50 workouts began with a weight considerably lighter than the maximum weight lifted for 10 repetitions (10-RM) so 1.00 40 subjects could complete 10-RM in the final set. When the 0.75 30 person achieved 10-RM, total repetitions equaled 70 to 100. For example, if 10-RM for the first week equaled 0.50 20 20 pounds, then beginning the first set with 2.5 pounds 0.25 10 and increasing 1.5 pounds after each 10-repetition set 0 0 accumulated 80 repetitions when performing the final 7 14 21 28 35 42

ted Training duration, d

20-pound 10-RM. f DeLorme advocated exercising once daily, 5 days Before training After 36 days weekly, with workouts not exceeding 30 minutes. The pa- 20 lb 1-RM 60 lb C han g e, in 20.5 in Thigh girth 22.4 in tient performed one maximal lift (1-RM) only once each Pounds li week. DeLorme believed that a person should exercise Time course of 1-RM (yellow line) and changes in thigh girth “smoothly, rhythmically, and without haste, but not so (red line) for a representative subject during 35 days of slowly that the mere holding of the weight would tire the progressive resistance exercise. 97818_ch22.qxd 8/4/09 4:44 PM Page 502

502 Section 4 Enhancement of Energy Transfer Capacity sets of exercises, each set consisting of 10 repetitions done between training sessions. Inadequate recovery consecutively without resting. The first set required one-half retards progress in neuromuscular and structural the maximum weight that could be lifted 10 times, or 1/2 adaptations and strength development. 10-RM; the second set used 3/4 10-RM, and the final 10-RM 9. A fast rate of moving a given resistance generates required maximum weight. As patients trained, the muscles of more strength improvement than moving at a slower the exercised limbs became stronger, so the 10-RM resistance rate. Neither free weights (barbells, weight plates, increased periodically to maintain continued strength improve- dumbbells) nor an array of exercise machines ments. Similar improvements occurred even when reversing shows inherent superiority for developing muscle the exercise intensity progression so patients performed the 10- strength. RM as the first set. 10. Exercise should sequence to optimize workout quality by engaging large before small muscle groups, multiple-joint exercises before single-joint exer- Variations of PRE. The following summarizes 13 gen- cises, and higher intensity exercise before lower in- eral findings from research studies on the optimal number of tensity exercise. sets and repetitions, including frequency and relative intensity 11. Combined resistance-training concentric and eccen- of PRE training for optimal strength improvement: tric muscle actions augment effectiveness; include 1. Eight- to 12-RM proves effective in novice training, both single-joint and multiple-joint exercises to whereas 1- to 12-RM effectively loads for interme- potentiate a muscle’s strength and fiber diate training. This can then increase to heavy size.121,222,230,246 loading using 1- to 6-RM. 12. Overload training that includes eccentric muscle 2. Rest 3 minutes between sets of an exercise at actions preserves strength gains better during a moderate movement velocity (1 to 2 s concentric; maintenance phase than concentric-only training.47 1 to 2 s eccentric). 13. Power training should apply the strategy to improve 3. For PRE at a specific RM load, increase load 2 to muscular strength plus include lighter loads (30 to 10% when the individual performs 1 to 2 repetitions 60% of 1-RM) performed at fast contraction veloc- above the current workload. ity. Use 2- to 3-minute rest periods between sets. 4. Performing one exercise set induces only slightly Emphasize multiple-joint exercises that activate less strength improvement in recreational weight large muscle groups. lifters than performing two or three sets.38,95 For TABLE 22.2 summarizes the major recommendations of those who desire to maximize muscle strength and the American College of Sports Medicine position stand on size gains, higher volume, multiple-set paradigms progression in resistance training for healthy adults. emphasizing 6- to 12-RM at moderate velocity with 1- to 2-minute rests between sets prove most effective. Periodization. In 1972, Russian scientist Leonid 5. Single-set programs generally produce most of the Matveyev introduced the concept of strength-training health and fitness benefits of multiple-set programs. periodization;163 it has since become incorporated into the These “lower volume” programs also produce training regimens of novice and champion athletes in- greater compliance and reduce financial cost and volved in resistance training.32,120,137,139,208 Conceptually, time commitment. periodization varies training intensity and volume to en- 6. Novices and intermediates should train 2 to 3 days a sure that peak performance coincides with major competi- week, whereas the advanced can train 3 to 4 days a tion. It also proves effective for achieving recreational and week. Such a generalization is not without a poten- rehabilitative goals. Periodization subdivides a specific tial downside. High training frequency extends the resistance-training period such as 1 year (macrocycle) into transient activation of inflammatory signaling cas- smaller periods or phases (mesocycles), with each mesocy- cades, concomitant with persistent suppression of cle again separated into weekly microcycles. In essence, key mediators of anabolic responses, which could the training model progressively decreases training volume blunt the training response.45 and increases intensity as duration of the program pro- 7. Training twice every second day produces overall gresses to maximize gains in muscular strength and power. superior results compared with daily training.92 This Fractionating the macrocycle into components allows ma- may occur from the effects of low muscle glycogen nipulation of training intensity, volume, frequency, sets, content (with training twice every second day) on repetitions, and rest periods (to prevent overtraining). It enhanced transcription of genes involved in training also provides a way to alter workout variety. Periodization adaptations.229 variation can reduce negative overtraining or “staleness” 8. If training includes multiple exercises, 4 or 5 days effects so athletes achieve peak performance at competi- per week may produce less improvement than train- tion. FIGURE 22.9 (top) depicts the generalized design for ing 2 or 3 times per week because near-daily train- periodization and a typical macrocycle’s four distinct ing of the same muscles impairs muscle recuperation phases. As competition approaches, training volume 97818_ch22.qxd 8/4/094:44PMPage503

TABLE 22.2 • Summary of Resistance Training Recommendations: an Overview of Different Program Variables Needed for Progression with Different Fitness Levels

Muscle Action Selection Order Loading Volume Rest Intervals Velocity Frequency

Strength For Nov, Int, Adv: For Nov, Int, Adv: Nov. ECC & CON SJ & MJ ex. Large Ͻ small 60Ð70% of 1RM 1Ð3 sets, 8Ð12 reps 2Ð3 min for core S, M 2Ð3ϫ/week Int. ECC & CON SJ & MJ ex. MJ Ͻ SJ 70Ð80% of 1RM Mult. sets, 6Ð12 reps 1Ð2 min for others M 2Ð4ϫ/week Adv. ECC & CON SJ & MJ ex.— HI Ͻ LI 1RM—PER Mult. sets 1Ð12 US-F 4Ð6 ϫ/week emphasis: MJ reps—PER

Hypertrophy For Nov, Int, Adv: Nov. ECC & CON SJ & MJ ex. Large Ͻ small 60Ð70% of 1RM 1Ð3 sets, 8Ð12 reps 1Ð2 min S, M 2Ð3ϫ/week Int. ECC & CON SJ & MJ ex. MJ Ͻ SJ 70Ð80% of 1RM Mult. sets, 6Ð12 1Ð2 min S, M 2Ð4ϫ/week Adv. ECC & CON SJ & MJ HI Ͻ LI 70Ð100% of 1RM with Mult. sets 1Ð12 2–3 min—VH; S, M, F 4Ð6ϫ/week emphasis on reps with emphasis 1–2 min—L-MH 70–85%—PER on 6–12 reps—PER

Power For Nov, Int, Adv: For Nov, Int, Adv: For Nov, Int, Adv: For Nov, Int, Adv: Nov. ECC & CON Mostly MJ Large Ͻ small Heavy loads Train for strength 2Ð3 min for core M 2Ð3ϫ/week (Ͼ80%)—strength; Light (30Ð60%) —velocity—PER Int. ECC & CON Most complex 1Ð3 sets, 3Ð6 reps 1Ð2 min for others F 2Ð4ϫ/week Ͻ least complex Adv. ECC & CON HI Ͻ LI 3–6 sets, 1–6 reps—PER F 4Ð6 ϫ/week

Endurance For Nov, Int, Adv: For Nov, Int, Adv: For Nov, Int, Adv: Nov. ECC & CON SJ & MJ ex. Variety in sequencing 50Ð70% of 1RM 1Ð3 sets, 10Ð15 reps 1Ð2 min for S—MR 2Ð3ϫ/week recommended high rep sets Int. ECC & CON SJ & MJ ex. 50Ð70% of 1RM Mult. sets, 10Ð15 Ͻ1 min for M—HR 2Ð4ϫ/week reps or more 10Ð15 reps Adv. ECC & CON SJ & MJ 30–80% of 1RM—PER Mult. sets, 10Ð25 4Ð6 ϫ/week reps or more—PER

ECC, eccentric; CON, concentric; Nov, novice; Int, Intermediate; Adv, advanced; SJ, single-joint; MJ, multiple-joint; ex., exercises; HI, high intensity; LI, low intensity; 1RM, 1-repetition maximum; PER, periodized; VH, very heavy; L-MH, light-to-moderately heavy; S, slow; M, moderate; US, unintentionally slow; F, fast, MR, moderate repetitions; HR, high repetitions. From ACSM position stand on: Progression models in resistance training for healthy adults. Med Sci Sports Exerc 2002;34:364. 503 97818_ch22.qxd 8/4/09 4:44 PM Page 504

504 Section 4 Enhancement of Energy Transfer Capacity

Model for periodization Mesocycle 1 Mesocycle 2 Mesocycle 3 Mesocycle 4

Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Preparation First Competition Second transition phase transition phase (active recovery)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Volume Intensity Technique Active rest Peak

Figure 22.9 • Top. Periodization subdivides a macrocycle into distinct phases or mesocycles. These in turn separate into weekly microcycles. The general plan provides modifications, but mesocycles typically include four parts: (1) preparation phase, (2) first transition phase, (3) competition phase, and (4) a second transition or active recovery phase. Bottom. Example of periodization for an elite athlete (gymnast) preparing for competition. Competitions took place throughout the yearly training program so periodization focused on achieving peak performance at the end of each macrocycle. Periodization places training into context for intensity, duration, and frequency of strength–power workouts. The major purpose of this focus attempts to avoid overtraining (staleness), minimize injury potential, and reduce training monotony, while progressing toward peak competition performance (filled circles).

gradually decreases while training intensity concurrently 90% 1-RM plus flexibility and interval aerobic increases. training). ¥ Competition phase lets the participant peak for com- ¥ Preparation phase emphasizes modest strength petition. Selective strength development is empha- development with high-volume (3Ð5 sets, 8Ð12 reps), sized with low-volume, high-intensity workouts low-intensity workouts (50 to 80% 1-RM plus flexi- (3Ð5 sets, 2Ð4 reps at 90 to 95% 1-RM plus short bility and aerobic and anaerobic training). periods of interval training that emphasize sport- ¥ First transition phase emphasizes strength specific exercises). development with workouts of moderate volume ¥ Second transition phase (active recovery) empha- (3Ð5 sets, 5Ð6 reps) and moderate intensity (80 to sizes recreational activities and low-intensity workouts 97818_ch22.qxd 8/4/09 4:44 PM Page 505

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 505 that incorporate different exercise modes. For the Resistance Training Guidelines for Sedentary next competition, the athlete repeats the periodization Adults, the Elderly, and Cardiac Patients: cycle. Benefits in Health and Disease Periodization structures an inverse relation between train- Currently, the American College of Sports Medicine (www. ing volume and training intensity through the competition acsm.org), American Heart Association (www.americanheart. phase; it then decreases both aspects during the second transi- org/), Centers for Disease Control and Prevention (www.cdc. tion or recuperation period. Note the increase in time devoted gov/), American Association of Cardiovascular and Pulmonary to technique training as competition approaches, with training Rehabilitation (www.aacvpr.org/), and the U.S. Surgeon volume at the periodization cycle’s lowest point. The bottom General’s Office (www.surgeongeneral.gov/) consider regular part of Figure 22.9 shows how training volume and intensity resistance exercise an important component of a comprehen- interact within a mesocycle for an athlete in a specific sport. sive, health-related physical fitness program.3,10,76,201,255 Sport-specific training principles usually apply in peri- Resistance training goals for competitive athletes focus on odization to design a training regimen based on a sport’s dis- optimizing muscular strength, power, and hypertrophy (high- tinct strength, power, and endurance requirements. A detailed intensity with 1-RM to 6-RM training loads). In contrast, analysis of metabolic and technical requirements of the sport goals for most middle-aged and older adults focus on mainte- also frames the training paradigm. The concept of periodiza- nance (and possible increase) of muscle and bone mass and tion makes intuitive sense, yet limited data exist for the supe- muscular strength and muscular endurance to enhance the riority of this training approach. Periodized resistance overall health and physical-fitness profile.39,110,146,148 Adequate training has produced greater improvements in upper- and muscular strength in midlife maintains a margin of safety lower-body muscular strength and sport-specific motor per- above the necessary threshold to prevent injury in later life.28 formance than a traditional resistance-training program in Among 45- to 68-year-old men, hand-grip strength accurately collegiate women tennis players.107 predicted functional limitations and disability 25 years later Researchers have studied shorter mesocycles to deter- (FIG. 22.10). Men in the lowest one-third for grip strength mine what combination of factors optimizes performance im- showed the greatest risk; those in the middle one-third showed provements. One study that equated training volume and intermediate risk; and men in the top one-third experienced the intensity among three approaches to periodization (linear pe- least disability risk at the 25-year follow-up. The resistance- riodization, undulating periodization, and a nonperiodized training program recommended for middle-aged and older time interval) found each training method equally effective.17 men and women classifies as “moderate intensity.” In contrast The training groups made similar gains in muscular strength to the multiple-set, heavy-resistance approach of younger (25% squat, 13.1% bench press) and muscular power (7.6% athletes, the program uses single sets of diverse exercises per- vertical jump). Without equating training volume and inten- formed between 8- and 15-RM a minimum of twice weekly. sity, it is impossible to evaluate differences in training effects TABLE 22.3 presents guidelines from different groups and health reported previously.276 organizations for prudent resistance training of older men and A critical review of the few studies of periodized strength women and cardiac patients. training concluded that this approach produced greater improvements in muscular strength, body mass, FFM, and percentage body fat than nonperiodized multiset and single-set Does Resistance Training Plus Aerobic training programs.75 Research must evaluate how periodiza- Training Equal Less Strength Improvement? tion interacts with fitness status, age, gender, and specific Debate concerns whether concurrent resistance and aero- sports (motor) performance. Studies must equate participants bic training yields less muscular strength and power improve- on various fitness parameters and then manipulate different ment than training for strength only.22,84,138,169 This has training protocols, accounting for factors that affect training caused many strength and power athletes and bodybuilders to response. Program evaluation must consider the following refrain from including endurance activities in the belief they four factors: diminish strength improvements. Advocates for abstaining 1. Biomechanical and motor control sequences in the from aerobic training when attempting to optimize gains in targeted sport skill muscle size and strength maintain that the added energy (and 2. Changes in segmental and whole-body composition perhaps protein) demands of intense endurance training limit 3. Biochemical and ultrastructural tissue adaptations a muscle’s growth and metabolic responsiveness to resistance 4. Transfer of newly acquired strength to subsequent training. Some data support this position. For example, differ- sport performance measures ent modes of exercise induce antagonistic molecular level, intracellular signaling mechanisms that could exert a negative impact on the muscle’s adaptive response to resistance train- INTEGRATIVE QUESTION ing.179 For example, endurance exercise training may inhibit Discuss the statement “There is no one best signaling to the muscles’ protein-synthesis machinery, which system of resistance training.” would definitely be counterproductive to the goals of resistance training.27,130,280 97818_ch22.qxd 8/4/09 4:44 PM Page 506

506 Section 4 Enhancement of Energy Transfer Capacity

Doing heavy household work

Walking 0.8km

Walking up to 10 steps

Lifting 4.5kg

Dressing

S elf-reported difficulty Bathing

100

60 20

50 30 Toileting 40

Eating

Walking speed ≤0.4m.s–1

Unable to rise Functional

limitations from a chair

0 5 10 15 20 25 30 Percentage

Grip strength tertiles Highest Middle Lowest

Figure 22.10 • Relationship between grip strength assessed in 3218 healthy middle-aged 45- to 68-year-old men and functional limitations and difficulties 25 years later. (From Rantanen T, et al. Midlife hand grip strength as a predictor of old age disability. JAMA 1999;281:558.)

A short-term bout of high-intensity endurance exercise also preadolescents, largely because of limited data on the topic. inhibits performance in subsequent muscular strength activi- Obvious concern arises regarding the potential for injury from ties.152 Further research must determine whether this acute effect excessive musculoskeletal loading (epiphyseal fractures, on maximal force output limits ability to overload skeletal mus- ruptured intervertebral disks, lower back bony disruptions, cle optimally to a degree that impairs strength development with acute low back trauma). A child’s hormonal profile also lacks concurrent strength and endurance training. If it does, then a 20- full development—particularly the tissue-building hormone to 30-minute recovery between aerobic and strength-training testosterone (refer to Chapter 20). One might question components might enhance the quality of subsequent strength whether resistance training in children could even induce sig- workout. These considerations should not deter those who desire nificant strength improvements. a well-rounded conditioning program that offers specific fitness Supervised resistance training using concentric-only and health benefits from incorporating both training modes.64,110 muscle actions with relatively high repetitions and low resistance improves muscular strength of children and adolescents without adverse effect on bone, muscle, or connective Resistance Training for Children tissue.69,197,274 More than likely, learning and enhanced Many textbooks in exercise physiology do not focus on neuromuscular activation rather than substantial increases in the benefits and possible risks of resistance training for muscle size account for children’s relatively rapid strength 97818_ch22.qxd 8/5/09 12:07 AM Page 507

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 507

TABLE 22.3 • Strength-Training Guidelines for Sedentary Adults, Elderly Persons, and Cardiac Patients Number of Frequency Guideline Sets Repetitionsa Exercises (Days/Week)

Healthy sedentary adults 1990 ACSM Position Standb 1 8Ð12 8Ð10c 2 1995 ACSM Guidelinesd 1 8Ð12 8Ð10 2 1996 Surgeon General’s Reporte 1Ð2 8Ð12 8Ð10 2 Elderly persons Pollock et al,f 1994 1 10Ð15 8Ð10 2 Cardiac patients 1995 AHA Exercise Standardsg 1 10Ð15 8Ð10 2Ð3 1995 AACVPR Guidelinesh 1 10Ð15 8Ð10 2Ð3

From ACSM, American College of Sports Medicine; AHA, American Heart Association; AACVPR, American Association of Cardiovascular and Pulmonary Rehabilitation. a For healthy persons under age 50, weight should be sufficient to induce volitional fatigue with the number of repetitions listed. For older persons, lighter loads may be used. b American College of Sports Medicine. The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness in healthy adults. Med Sci Sports Exerc 1990;22:265. c Minimum one exercise per major muscle group (e.g., chest press, shoulder press, triceps extension, biceps curl, pull-down [upper back], lower back extension, abdominal crunch/curl-up, quadriceps extension, leg curls [hamstrings], calf-raise). d American College of Sports Medicine. Guidelines for exercise testing and prescription. 5th ed. Baltimore: Williams & Wilkins, 1995; also included low- risk diseased populations. e U.S. Department of Health and Human Services. Physical activity and health: a report of the surgeon general. Atlanta: US Dept. of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, 1996. f Pollock ML, et al. Exercise training and prescription for the elderly. South Med J 1994;87:S88. g Fletcher GF, et al. Exercise standards: a statement for health care professionals from the American Heart Association. Circulation 1995;91:580. h American Association of Cardiovascular and Pulmonary Rehabilitation. Guidelines for Cardiac Rehabilitation Programs. 2nd ed. Champaign, IL: Human Kinetics, 1995.

IN A PRACTICAL SENSE The Lower Back

”In the developed world, musculoskeletal disorders are the most fre- about $90 billion yearly in related health costs. Most cases result quent causes of physical disability. As the aging global population in- from on-the-job injuries, particularly men in lumber and building creases, the prevalence of many musculoskeletal disorders will increase retailing (highest risk) and construction (most cases); major-risk in- in both the developed and developing parts of the world with the likely dustries for women include nursing and personal care centers result being an increase in the number of people with chronic disabling (highest risk) and hospitals (most cases). Grocery stores and agri- disorders. This will have a definite negative impact on healthcare provi- cultural crop production rank among the top 10 occupations for sion and the economies of countries in the coming years.” lower back injury for men and women. Estimates indicate that at The burden of musculoskeletal conditions at the start of the new mil- least 32 million adult Americans frequently experience lower back lennium; WHO Technical Report Series 919 (World Health Organization, pain, the primary cause for workplace disability.145 Workplace dis- Geneva) 2003. 218 pages. ability from injuries to the lower back region also occurs in common According to the Bone and Joint Decade Monitor Project and the tasks like refuse collection and other manual handling and lifting World Health Organization (WHO) (www.ota.org/downloads/ tasks.59,63,132 bjdExecSum.pdf), the total costs in the United States related to Muscular weakness, particularly in the abdominal and lower musculoskeletal conditions exceeds $250 billion yearly. Of this lumbar back regions, lumbar spine instability, and poor joint flexi- amount, direct costs account for $88.7 billion. Thirty-eight percent bility in the back and legs represent primary external factors related was spent on hospital admissions, 21% on nursing home admis- to low back pain syndrome.228 sions, 17% on physician visits, and 5% on administrative costs. Prevention of and rehabilitation from chronic low back strain Indirect costs account for 58% of the total ($126.2 billion), which commonly use muscle-strengthening and joint-flexibility exer- include lost wages through morbidity or premature mortality. cises.23,70,171,212,263 Continuing normal activities of daily living Musculoskeletal diseases include approximately 150 different dis- (within limits dictated by pain tolerance) yields more rapid recovery eases and syndromes typically associated with pain or inflamma- from acute back pain than bed rest. Maintaining normal physical tion. Back injuries account for one-fourth of all work-related injuries activity facilitates greater recovery than specific back-mobilizing and one-third of all compensation costs, which, according to the exercises performed after pain onset.161 Prudent use of resistance-type Bureau of Labor Statistics (www.bls.gov/), cost the government training isolates and strengthens the abdomen and lower lumbar

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508 Section 4 Enhancement of Energy Transfer Capacity

IN A PRACTICAL SENSE Continued

extensor muscles that support and protect the spine through its full segment of the spine equivalent to 6 to 10 times body mass.36,43 A range of motion. Patients with low back pain who strengthen the person who weighs 90 kg and squats with 144 kg can create peak lumbar extensors with the pelvis stabilized experience less pain, compressive forces in excess of 1367 kg (13,334 N)! A sudden fewer chronic symptoms, and improved muscular strength and amplification of compressive force can precipitate anterior disk endurance and range of motion.37 prolapse; a lower-intensity but sustained compressive force that Weak Link™ Testing, or WLT, is a relatively new Norwegian produces fatigue can increase posterior bulging of the lamellas in methodology to assess low back/hip instability using a sling support the posterior annulus.6 In national-level male and female power- system that features closed kinetic chain movements combined lifters, average compressive loads on L4–L5 reached 1757 kg with manual vibration added to the slings (www.redcord.com). (17,192 N).173 At the practical level, during sports training with re- In the example illustrated below, the initial body position isolates sistance methods (i.e., functional training with free weights), one the gluteus medius muscle whose function stabilizes hip flexion/ should not sacrifice proper execution of an exercise to lift a heavier extension and inward and outward rotational movements. Golfers load or “squeeze out” additional repetitions. The extra weight with poor initial hip rotation during the downward phase of the lifted through improper technique does not facilitate muscle swing often exhibit poor hip and spinal rotation, primarily from strengthening; instead, improper body alignment or unwarranted weak (or deactivated) gluteus medius muscle action. Reactivating muscle substitution during force production can trigger debilitat- this key muscle with closed kinetic chain movements combined ing injury where surgery unfortunately becomes the option of with vibration may help to alleviate the inefficient slide phase during choice. This fact of life should encourage proper strengthening of the golf swing to restore effective hip rotation. Biomechanical “core” abdominal and lower back muscles (with lower back and analysis of the golf swing has provided insight into the rudiments hip exercises, as those depicted on pages 509–510, to avoid either of golf mechanics and injury incidence and disability in amateur prolonged reliance on pain-relieving drugs or potentially debilitat- and professional golfers.68,82,150,265,288 ing surgical alternatives. Wearing a relatively stiff weightlifting belt during heavy lifts (squats, dead lifts, clean-and-jerk maneuvers) reduces intraabdominal pressure compared with lifting without a belt.42,81,93,144 The belt reduces potentially injurious compressive forces on spinal disks during near-maximal lifting, including most Olympic and powerlifting events and associated training. In one study, nine experienced weightlifters lifted barbells up to 75% body weight under three conditions: (1) while inhaling and wearing a belt, (2) inhaling and not wearing a belt, and (3) exhaling and wearing a belt.133 Measurements included intraabdominal pressure, trunk muscle EMG, ground reaction forces, and kinematics. The belt reduced compression forces by about 10%, but only when inhaling before lifting. The authors concluded that wearing a tight and stiff-back belt while inhaling before lifting reduces spinal loading during the lift. A person who normally trains wearing a belt should generally refrain from lifting without one. Further recommendations include performing at least some submaximal resistance training without a belt to strengthen the deep abdominal and pelvic stabilizing muscles. This also develops the proper pattern of muscle recruitment to generate high intraabdominal pressures when not wearing a belt. Wearing a back belt to increase intraabdominal pressure to amelio- rate low back injuries in the workplace does not provide a clear-cut biomechanical advantage.198 A 2-year prospective study of nearly 14,000 material-handling employees in 30 states evaluated the effectiveness of using back belts to reduce back injury worker’s compensation claims and reports of low back pain.270 Neither frequent back belt use (usually once a day, once or twice a week) nor a store policy (Sling and rope photos courtesy of Frank Katch, Santa Barbara, CA, that required the use of these belts reduced injury or reports of low and Oyvind Pedersen, Redcord Clinic, Santa Barbara, Santa back pain. Researchers continue to probe for answers about the etiol- Barbara, CA.) ogy of low back pain syndrome and how to minimize its severity and reduce its occurrence.125,214,221,275 Studies have focused on numer- Improper performance of a typical resistance-exercise move- ous contributing factors that include intradisk pressure;174 facet loads ment (with a relatively heavy load and the hips thrust forward with and disk fiber strains;223 lumbar disk height and cross-sectional arched back) creates considerable compressive force on the lower area;182 compressive follower loads;196 spinal joint force distribu- spine. For example, pressing and curling exercises with back hy- tion;41 ligament strain, disk shear, and facet impingement;78 and pre- perextension create unusually high shearing stress on the lumbar diction models to estimate spinal compression and shear forces.88,128 vertebrae, often triggering low back pain accompanied by muscle The following 12 exercises provide general strengthening of the instability in this region.14,97,102 Compressive forces with heavy abdomen, pelvic region, and lower back, and improve hamstring lifting also can hasten damage to the disks that cushion the and lower back flexibility for individuals with no apparent lower vertebrae. Performing half squats with barbell loads from 0.8 to back and spinal injuries. Symptomatic individuals (including ath- 1.6 times body mass produces compressive loads on the L3–L4 letes) require specific back exercises.204,219

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CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 509

IN A PRACTICAL SENSE Continued

I. Lower back stretches (hold each exercise for 30 to 60 s) 4. Allah stretch: Sit, buttocks on bilateral heels; move hands as 1. Knees-to-chest stretch: Lie supine and pull the knees into the far as possible forward along the surface. chest while keeping the lower back flat on the surface.

II. Abdominal exercises 2. Cross-leg stretch: Cross the legs and pull one 90°-flexed knee 5. Bent-knee sit-up: Keep hands low on neck (or across chest) toward the chest. with the head positioned over the shoulders. Roll up slowly, engaging one row of the abdominals at a time. Raise shoulders 4 to 6 inches off the surface.

3. Hamstring stretch: Wrap a strap over the foot, keeping lower back flat; pull leg upward toward the head. 6. Dying bug: Flex the pelvis to flatten lower back against the surface. Over one side bring an extended arm and flexed knee together. On opposing side, extend arm straight overhead and leg straight backward. Maintain pelvic flexion while exchanging opposing arms and legs in this position.

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510 Section 4 Enhancement of Energy Transfer Capacity

IN A PRACTICAL SENSE Continued

III. Prone lumbar extension exercises 10. Pointer (bird dog): Start with hands and knees on the 7. Dry-land swimming: Lying prone with pelvic flexion, alter- floor. Flex pelvis into a counter position. Exchange by nately lift opposite arm and leg. pointing opposite arm and leg while keeping torso level.

8. Both legs up: Lie prone with pelvic flexion, and lift both legs simultaneously while keeping the head on the floor. IV. Supine pelvic-flexion exercises 11. Leg pointer: Lie supine on the floor and flex pelvis with lower abdominals to flatten the lower back into the surface. Extend one arm upward and one leg outward while keeping quadriceps level.

9. Upper-body up: Lying prone with pelvic flexion and arms outstretched or behind the back, lift upper torso while keeping legs on the floor. 12. Prone cobra push-up: Keep pelvis on the floor while pressing up with arms to produce lower back extension.

(Photos courtesy of Dr. Bob Swanson, Santa Barbara Back and Neck Care, Santa Barbara, CA) 97818_ch22.qxd 8/4/09 4:44 PM Page 511

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 511

TABLE 22.4 • Guidelines for Resistance-Exercise Training and Progression in Children and Adolescents Age (Y) Considerations

7 or younger Introduce child to basic exercises with little or no weight; develop the concept of a training session; teach exercise techniques; progress from body weight calisthenics, partner exercises, and lightly resisted exercises; keep volume low. 8Ð10 Gradually increase the number of exercises; practice exercise technique in all lifts; start gradual progressive loading of exercises; keep exercises simple; gradually increase training volume; carefully monitor toleration to the exercise stress. 11Ð13 Teach all basic exercise techniques; continue progressive loading of each exercise; emphasize exercise techniques; introduce more advanced exercises with little or no resistance. 14Ð15 Progress to more advanced youth programs in resistance exercise; add sport-specific components; emphasize exercise techniques; increase volume. 16 or older Move child to entry-level adult programs after all background knowledge has been mastered and a basic level of training experience has been gained.

From Kraemer WJ, Fleck SJ. Strength training for young athletes. Champaign, IL: Human Kinetics, 1993. Note: If a child of any age begins a program without previous experience, start the child at lower levels and move to more advanced levels as exercise toleration, skill, amount of training time, and understanding permit.

193 improvements. The guidelines in TABLE 22.4 provide pru- weakness at a particular angle in the ROM, thus forming a dent recommendations for initiating resistance exercise train- basis for optimizing muscle overload at an appropriate joint ing for children and adolescents. angle.

Isometric Strength Training Which Are Better: Static or Dynamic Methods? Research in Germany during the mid-1950s showed that isometric strength increased about 5% weekly by performing Static and dynamic resistance training methods each increase a daily single, maximum isometric muscle action of only muscle “strengths.” An individual’s specific needs determine 1-second duration, or a 6-second action at two-thirds maxi- the optimal resistance training method governed by the speci- mum.104 Repeating this action 5 to 10 times daily produced ficity of the training response.177,287 greater gains in isometric strength. Specificity of Training Response Isometric Exercise Limitations An isometrically trained muscle shows greatest strength improvement when measured isometrically; simi- Isometric exercise provides muscle overload and im- larly, a dynamically trained muscle tests best when evalu- proves strength yet offers limited benefits for functional ated in resistance activities that require movement. sports training. Without movement, one cannot readily evalu- Isometric strength developed at or near one joint angle does ate the overload level and/or training progress. Also, a high not readily transfer to other angles or body positions that degree of specificity affects isometric strength development. must rely on the same muscles.272 In dynamic exercise, mus- A muscle trained isometrically clearly improves strength pri- cles trained through movement over a limited ROM show marily when the muscle acts isometrically, particularly at the the greatest strength improvement when measured in that training joint angle and body position. This means that iso- ROM.20,86 Even body position specificity exists; muscular metric training to develop “strengths” for a particular move- strength of ankle plantar and dorsiflexors developed in the ment probably necessitates training at many specific angles standing position with concentric and eccentric muscle ac- through the ROM. This becomes time consuming, particu- tions showed no transfer with the same muscles evaluated in larly given the availability of conventional dynamic weight the supine position.202 Resistance training specificity makes training and isokinetic and other functional resistance training sense because strength improvement blends adaptations in methodologies. two factors: 1. The muscle fiber and connective tissue harness itself Isometric Exercise Benefits 2. Neural organization and excitability of motor units The isometric method benefits muscle testing and reha- that power discrete patterns of voluntary move- bilitation. Isometric techniques can detect specific muscle ment155,181,203,233 97818_ch22.qxd 8/4/09 4:44 PM Page 512

512 Section 4 Enhancement of Energy Transfer Capacity Likewise, a muscle’s maximal force output depends on Evaluating leg extension peak torque of the same leg with an neural factors that effectively recruit and synchronize firing isokinetic dynamometer detected only a 10 to 17% improve- of motor units, not just local factors such as muscle fiber type ment!59,77 To improve a specific physical performance through and cross-sectional area.48,129,226 resistance training, one must train the muscle(s) in movements A 3-month study of young adult men and women empha- that mimic the movement requiring forceÐcapacity improve- sized the highly specific nature of resistance-training adapta- ment, with focus on force, velocity, and power requirements tions.65 One group trained the adductor pollicis muscle rather than simply an isolated joint or muscle. isometrically with 10 daily actions of 5-seconds duration at a frequency of 1 per minute. The other group trained the same Physical Testing in the Occupational Setting: muscle dynamically with 10 daily 10-repetition bouts of weight The Role of Specificity movement at one-third maximal strength. The untrained muscle served as the control. To eliminate any training influence A comprehensive review outlines the development of from psychologic factors and central nervous system adapta- physical tests and professionally and legally defensible tions, a supermaximal electrical stimulation applied to the validation strategies for preemployment occupational test- motor nerve evaluated the force capacity of the trained mus- ing requiring diverse physical abilities or specific fitness cle. The results were clear—both training groups improved characteristics.122 The high specificity of components of maximal force capacity and peak rate of force development. physical performance and physiologic function (e.g., mus- The improvement in maximal force for the isometrically cular strength and power, joint flexibility, aerobic fitness) trained group nearly doubled the improvement for the dynam- combined with the specific nature of the training response ically trained group. Conversely, improvement in speed of casts serious doubt that broad constructs of physical fitness force development averaged about 70% greater in the group exist to any important extent. Clearly, no single measure of trained with dynamic muscle actions. Such findings provide overall muscular strength or aerobic fitness exists. Instead, strong evidence that resistance training per se does not induce an individual expresses an array of muscular strengths and all-inclusive (general) adaptations in muscle structure and powers and aerobic “fitnesses.” These expressions of mus- function. Rather, a muscle’s contractile properties (maximal cle function and exercise performance often relate poorly to force, velocity of shortening, rate of tension development) each other if at all. Likewise, testing a person for aerobic improve in a manner highly specific to the muscle action in fitness produces different fitness scores depending on the training. Both static and dynamic training methods produce activity. For example, it would be undesirable to administer strength increases, yet no one system rates consistently supe- the 12-minute run test (a test that purports to assess aerobic rior to the other in how best to assess muscle function. The capacity; refer to Chapter 21) in the occupational setting to crucial consideration concerns the intended purpose of the infer aerobic capacity for firefighting or lumbering (both newly acquired strength. requiring considerable upper-body aerobic function), or measuring static-grip or leg strength with tests to assess Practical Implications. The complex interaction be- diverse dynamic strengths and powers required in these tween nervous and muscular systems helps explain why leg occupations. muscles strengthened in squats or deep knee bends fail to show Measurements applied in the occupational setting should equivalent improved force capability in other leg movements closely resemble the actual requirements of the job (i.e., func- such as jumping or leg extension.183 Low relationships emerge tional tests), not only for specific tasks but also in a manner between dynamic measures of leg extension force at any speed that reflects the intensity, duration, and pace (i.e., physiologic and vertical jumping height. A muscle group strengthened and demands) of the job. If such “content testing” remains im- enlarged by dynamic resistance training does not demonstrate practical, one must substantiate alternative testing based on equal improvement in force capacity when measured isometri- carefully conducted validation studies. cally or isokinetically.226 Consequently, strengthening muscles for a specific athletic or occupational activity (e.g., golf, ten- INTEGRATIVE QUESTION nis, rowing, swimming, football, firefighting, package handling) demands more than just identifying and overloading the Advise a candidate for a firefighter’s job about muscles in the movement. It requires neuromuscular training the most effective way to train for a physical test specifically in the important movements that necessitate im- that requires 7 minutes of a series of job-related proved strength. A more appropriate name for this type of tasks (e.g., stair climb with equipment, hose drag, training is functional strength training or functional re- ladder raise, forcible entry with sledge hammer, sistance movement training.7,9,46,237 Increasing leg muscle simulated rescue dummy drag). “strength” through general weightlifting will not necessarily improve performance in a variety of subsequent leg move- 168 ments. Newly acquired strength seldom transfers fully to Isokinetic Resistance Training other types of strength movements, even those that activate the same trained muscles. A standard program of weight training Isokinetic resistance training combines the positive features for leg extension increased leg extension strength by 227%. of isometric exercise and dynamic weightlifting. It provides 97818_ch22.qxd 8/4/09 4:44 PM Page 513

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 513 muscle overload at a preset constant speed while the muscle Isokinetics Versus Standard Weightlifting mobilizes its force-generating capacity throughout the full ROM.213 Any effort during the exercise movement encoun- An important distinction exists between a muscle over- ters an opposing force to that applied to the mechanical loaded isokinetically and one overloaded with a standard device; this represents accommodating-resistance exercise. weightlifting exercise. FIGURE 22.11 shows that the force capacity Theoretically, isokinetic-type training activates the largest of a muscle (or muscle group) varies with the bony lever config- number of motor units to overload muscles consistently— uration (joint angle) as the joint moves through its ROM. During even at the relatively “weaker” joint angles—as the bone– weight training, the external weight lifted usually remains fixed muscleÐlever mechanics produce variations in force capacity at the greatest load that allows completion of the movement for throughout the ROM. Maintaining a constant movement the desired number of repetitions. Resistance cannot exceed the speed remains a negative aspect of isokinetic resistance train- maximum force generated at the weakest point in the ROM. If it ing because functional exercises rarely approximate a fixed did not, then one could not complete the movement. The term speed of movement. sticking point describes this area in the ROM.

Knee extension Knee flexion 100 100

75 75

50 50

25 25 Percentage of maximum force Percentage

0 0 40 80 120 160 160 120 80 40

Elbow extension Elbow flexion 100 100

75 75

50 50

25 25 Percentage of maximum force Percentage

0 0 40 80 120 160 160 120 80 40 Joint angle (degrees) Joint angle (degrees)

Figure 22.11 • Muscle force-generating capacity varies with joint angle in flexion and extension throughout the ROM. 97818_ch22.qxd 8/4/09 4:44 PM Page 514

514 Section 4 Enhancement of Energy Transfer Capacity The fact that muscles do not generate the same absolute higher percentages of fast-twitch fibers exerted greater torque maximum force through all movement phases represents a per unit body mass. This indicates the desirability of possess- major limitation of weightlifting. To help alleviate this prob- ing a high percentage of fast-twitch fibers for power activi- lem, manufacturers have devised variable-resistance train- ties, where success largely depends on capacity to generate ing equipment that adjusts resistance with the generalized torque at rapid movement velocities. lever characteristics of a particular joint movement. This equipment still represents a classic mode of weightlifting ex- Fast- Versus Slow-Speed Isokinetic Training cept the relative resistance offered to the muscle theoretically remains fairly constant with respect to muscle capacity at a Studies of strength and power improvement with isoki- particular shortening velocity throughout the ROM. With an netic training at slow and fast limb speeds further support the isokinetically loaded muscle, the desired movement speed oc- specificity of exercise performance and training response. For curs almost instantaneously with maximum force application, example, strength and power gains from slow-speed isoki- and the muscle generates peak power output throughout the netic training relate specifically to the angular velocity of the ROM at a controlled shortening velocity. movement in training. In contrast, exercising at fast speeds facilitates more general improvement; power output increased at fast and slow movement speeds, although measurement at Isokinetic Exercise and Training Experiments the fast angular velocity in training improved the most.199 Experiments with isokinetic exercise have explored the Muscle hypertrophy generally occurs from fast-speed training forceÐvelocity patterns in various movements related to mus- and mainly in the fast-contracting muscle fibers.50 Muscle cle fiber type composition. FIGURE 22.12 shows the progressive fiber hypertrophy may account for the more general strength decline in peak torque output with increasing angular velocity improvement with fast-speed training. Concentric muscle ac- of knee extensor muscles in two groups who differed in sports tions produce greater power increases and type II fiber hyper- training and predominant muscle fiber type. For movement at trophy from training than eccentric training at equivalent 180¡ и sÐ1, maximal torque decrement averaged about 55% of relative power levels.165 maximal isometric (0¡ и sÐ1) force. The two curves in Figure The attractiveness of isokinetic training allows muscular 22.12 differ in peak torque depending on the group’s muscle overload through a full ROM at many shortening velocities. fiber composition. Peak force at zero velocity (isometric Applications remain limited, however, because the most rapid force) remained similar for athletes with relatively high speed of movement of the current isokinetic dynamometers Ϫ (power athletes) or low (endurance athletes) percentages of approximates 400¡ и s 1. Even this relatively “fast” move- fast-twitch muscle fibers; this indicated activation of both ment speed does not approach limb speeds during sports fast- and slow-twitch motor units in maximal isometric knee activities. In baseball pitching, where upper-limb extension Ϫ extension. As movement velocity increased, individuals with velocity exceeds 2000¡ и s 1 in professional pitchers, even the relatively “slow” hip rotators move at 600° и sϪ1 during a pitch.35 Also, the present generation of isokinetic dynamometers cannot simultaneously overload eccentric muscle actions

)

1 that serve important functions in limb deceleration and “brak- – 3.5 ing” control in normal movements. 3.0 g B W k . 2.5 Plyometric Training 2.0 For sports that require powerful, propulsive movements— 1.5 football, volleyball, sprinting, high jump, long jump, and bas- 1.0 ketball—athletes apply a special form of exercise training termed plyometrics or explosive jump training.74,253,279 0.5 Plyometric exercise requires various jumps in place or re- 0 bound jumping (drop jumping from a preset height) to mobi- Peak torque (N-m Peak 90 180 270 360 450 540 630 720 810 Angular velocity (degrees . s–1) lize the inherent stretchÐrecoil characteristics of skeletal muscle and its modulation via the stretch or myotatic reflex. Stated somewhat differently, plyometric exercise involves Power athletes >60% FT Endurance athletes <50% FT rapid stretching followed by shortening of a muscle group during a dynamic movement. Stretching produces a stretch Figure 22.12 • Peak torque (per unit body mass) related to reflex and elastic recoil within muscle. When combined with angular velocity of joint movement in two groups of athletes a vigorous muscle contraction, plyometric actions should with different predominance of muscle-fiber type. The greatly increase the force that overloads the muscles, thereby torque–velocity curves were extrapolated (dashed line) to the 278 approximated maximal velocity for knee extension. (From facilitating increases in strength and power. Plyometric ex- Thorstensson A. Muscle strength, fiber types, and enzyme ercises range in difficulty from calf jumps off the ground to activities in man. Acta Physiol Scand Suppl 1976:443.) multiple one-leg jumps to and from boxes ranging in height 97818_ch22.qxd 8/4/09 4:44 PM Page 515

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 515 form of training, called ballistic resistance training, the person moves the weight or projectile as fast as possible while 1.50 trying to produce maximal force before releasing it. Sports

) 1.25 performance examples include shot put, overhead soccer 1 – throw, javelin and discuss throws, push away from the pole s . 1.00 vigorously in the pole vault, takeoff jump for a volleyball 0.75 spike, positioning and jumping for a basketball rebound, mul- y (m tiple punches in boxing, and takeoff in the high jump. 0.50 Plyometric exercise overloads a muscle to provide forcible and rapid stretch (eccentric or stretch phase) immediately before Velocit 0.25 the concentric or shortening phase of action. Recent reviews 0 0 102030405060708090100 summarize that the stretch-shortening cycle, or SSC, repre- Bar position relative sents an important concept that describes how skeletal muscles to total concentric movement (%) function efficiently in unrestricted human locomotor activities. When the muscle spindles of the gastrocnemius muscle suddenly become stretched, their sensory receptors fire with the im- Bench throw Bench press pulses traveling through the dorsal root into the spinal cord (to Figure 22.13 • Mean bar velocity in relation to total activate the anterior motor neurons) and trigger the stretch reflex concentric bar movement for bench throw and traditional (see Chapter 19), the timing of which relies on the speed of 53,117,118,135 bench press performed rapidly. (Data from Newton RU, movement. The sequence of stretching and shorten- et al. Kinematics, kinetics, and muscle activation during ex- ing muscle fibers (as in the contact phase of running) serves a plosive upper-body movements. J Appl Biomech 1996;12:31.) fundamental purpose—to enhance the final push-off phase. In many sports situations, the rapid lengthening phase in the SSC produces a more powerful subsequent movement from two from one foot to six feet. The basic principle for all jumping main factors:52,116,151,154,176,206,249 and plyometric exercises is to absorb the shock with the arms 1. Attainment of a higher active muscle state (greater or legs and then immediately contract the muscles. For exam- potential energy) before the concentric, shortening ple, when doing a series of squat jumps, jump again as action quickly into the air as possible after you land, while at the 2. Stretch-induced evoking of segmental reflexes that same time if possible, thrusting both heels up towards the but- potentiate subsequent muscle activation tocks. Quicker jumps provide greater overload to the muscles. In essence, “fast” plyometric exercise “trains” the nervous These two effects form the basis for the speedÐpower system to react quickly to activate muscles rapidly. benefits of this training mode.268,281 More than likely, im- Plyometric maneuvers avoid the disadvantage of having provement occurs from changes in the mechanical properties to decelerate a mass in the latter part of the joint ROM during of the muscle-tendon complex rather than changes in muscle 142 a fast movement; this provides for maximal power produc- activation strategies. FIGURE 22.14 shows the sledge er- tion. FIGURE 22.13 compares a traditional bench press move- gometer to (1) quantify force-generating capacity when af- ment to achieve maximal power output with a ballistic bench fected by the stretch-shortening cycle, (2) train under such throw that attempts to maximize power output by projecting conditions, and (3) evaluate stretch reflex sensitivity and the barbell from the hands. The results were unequivocal. muscle stiffness under fatiguing exercise. During a bench press, deceleration begins at about 60% of the bar position relative to the total concentric movement dis- Practical Application of Plyometrics tance (purple line). In contrast, velocity during the bench throw (yellow line) continues to increase throughout the ROM A plyometric drill uses body mass and gravity for the im- and remains higher at all bar positions after movement begins. portant rapid prestretch, or “cocking,” phase of the SCC to acti- This translates into greater average force, average power, and vate the muscle’s natural elastic recoil elements.54,114,186 Prior peak power outputs. Achieving a faster average and peak ve- stretch augments the subsequent concentric muscle action in locity throughout the ROM produces greater power output the opposite direction. Forcibly dropping the arms to the side and muscle activation (assessed by EMG) than the traditional before vertical jumping produces an eccentric prestretch of the weightlifting exercise movement. The throw condition pro- quadriceps muscle group and exemplifies a natural plyometric duced greater muscle activity for the pectoralis major movement. Lower-body plyometric drills include a standing (+19%), anterior deltoid (+34%), triceps brachii (+44%), and jump, multiple jumps, repetitive jumping in place, depth jumps biceps brachii (+27%). or drop jumping from a height of about 1 m, single- and dou- Allowing the athlete to develop greater power at the end ble-leg jumps, and various modifications. Proponents believe of the movement more closely simulates the projection phase that repetitive plyometric actions serve as neuromuscular train- of throwing an object (ball or implement), maximal effort ing to enhance power output of specific muscles and sport- jumping movements, or impact in striking movements. In this specific power performances as in jumping.100,143,170,285 97818_ch22.qxd 8/4/09 4:44 PM Page 516

516 Section 4 Enhancement of Energy Transfer Capacity

Brake-stretch Video of quadriceps monitor Sledge marker

Force plate

Video camera

Figure 22.14 • The sledge ergometer for plyometric (stretch-shortening cycle) exercise, training, and research protocols. Illustration shows braking phase (and subsequent muscle stretch) just prior to maximal activation of leg and foot extensor muscles. (Modified from Strojnik V, Komi PV. Fatigue after submaximal intensive stretch-shortening cycle exercise. Med Sci Sports Exerc 2000;32:1314.)

Although testimonials tout the benefits of plyometric movements may play a key role in “training” the sophisti- training, there is insufficient controlled evaluation of both cated signaling patterns involved in neuromuscular control of benefits and possible orthopedic risks of such workouts. human movements.15,26,62,71,162,194,250,252 Concern for musculoskeletal injury stems partly from the es- Recent studies using body weightÐsupported movements timation that drop jumping generates external skeletal loads in the sling and rope system during functional performance equal to up to 10 times body mass. Research must quantify training for soccer,238 golf,218 handball,217 and softball219 the appropriate role of plyometric drills in a complete show improvements in functional sport movements that range strengthÐpower training program, particularly for children from 3 to 5% in velocity of limb movement, increased golf and older recreational athletes. A position paper from the club head velocity and hence distance, and static and dynamic National Strength and Conditioning Association (www.nsca- balance and shoulder stabilization. Future research should as- lift.org/) suggests that athletes first achieve lifts of 1.5 times sess the effectiveness of the rope and sling methods versus body weight in the squat exercise before initiating high- conventional free weights, machines, and other resistance intensity plyometric training.278 This practical guideline training modalities to improve functional strength and subse- 264 requires validation. FIGURE 22.15 shows the rebound jumping quent performance in sport and rehabilitative modalities. technique in plyometric training along with four examples of plyometric exercise drills. Concept of the Core The last 10 years have seen a resurgence of “core training”— Body Weight-Loaded Training also referred to as lumbar stabilization, core strengthening, Body weight-loaded training using closed-kinetic chain ex- dynamic stabilization, neutral spine control, trunk stabiliza- ercise to enhance sports performance15,26,62,157,194 has gained tion, abdominal strength, core “pillar” training, and core- popularity and research support, including such training in functional strength training. job-related functions156 and treatment of pelvic pain follow- The core concept does not simply refer to muscles that ing pregnancy.239,240 cross the midsection of the body and form the “six-pack” ab- In weight-supported exercises (FIG. 22.16), the distal seg- dominals so commonly portrayed in magazine advertise- ment bears the body weight or part of the body weight. This ments. Rather, consider the core as a four-sided muscular type of exercise activates both agonists and antagonists mus- frame with abdominal muscles in front, paraspinals and cles about a joint, including other muscle groups along the gluteals in back, the diaphragm at the top, and the pelvic floor kinetic chain.234 Such training is often considered more func- and hip girdle musculature framing the bottom. This region tional compared to exercises where the distal segment is includes 29 pairs of muscles that hold the trunk steady, and nonÐweight bearing as in conventional weightlifting (where balance and stabilize the bony structures of the spine, pelvis, agonists and synergists are activated). In addition, body thorax, and other kinetic chain structures activated during weight-loaded exercise, as employed with the sling-system most movements.87 The totality of these spine-frame struc- apparatus (Fig. 22.16), introduces the added component of in- tures without adequate “strength and balance” would become stability, further challenging neuromuscular control of the mechanically unstable.190,192,195 A properly functioning core trunk and back muscles.235,241,242,251,254 The role of adding provides appropriate distribution of forces, optimal control and such perturbation during relatively simple and/or complex efficiency of movements, adequate absorption of ground-im- 97818_ch22.qxd 8/4/09 4:44 PM Page 517

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 517 Rebound Jumping Technique in Polymetric Training

A Stage 1 Stage 2 Stage 3

Rebound jump again after landing

OBJECTIVE: Complete 2-5 sets of 5-12 repetitions depending on strength level and conditioning base

20 inches

23 inches Starting position Jump onto the box Jump from the box

• Feet shoulder width • After landing, • Upon landing, explode apart explode upward as upward again onto • Flex ankles, knees, and high and as far forward another box, or as high hips and thrust vigorously as possible and far forward before forward and upward to rebound jumping again land with both feet on the box

Figure 22.15 • A. Rebound jumping technique in plyometric training. B. Four examples of plyometric exercise drills: (1) Box jump. (2) Cone hop. (3) Hurdle hop. (4) Long jump from box. (Examples of plyometric jumps courtesy of Dr. Thomas D. Fahey, California State University at Chico, Chico, CA.)

pact forces, and an absence of excessive compressive, transla- each component makes important neuromuscular contribution, and shearing forces on kinetic chain joints.127,172 tions to maximal power training. The window of adaptation opportunity shrinks for an athlete with already well- developed components and expands for components in need Window for Explosive Power Development of considerable improvement. As an athlete approaches his or FIGURE 22.17 lists five components that contribute to the her high-velocity strength potential, that component’s contri- window of explosive power development. In this model, bution to overall maximal power development diminishes. 97818_ch22.qxd 8/4/09 4:44 PM Page 518

518 Section 4 Enhancement of Energy Transfer Capacity Summary 1. Tensiometry, dynamometry, 1-RM testing with weights, and computer-assisted force and work- output determinations including isokinetic-type measurements provide the most common methods to measure muscular performance. 2. Human skeletal muscle generates a maximum force of about 30 N per cm2 of muscle cross section, regardless of gender. On an absolute basis, men generally exert greater maximal force than Figure 22.16 • Example of a push-up exercise using the women. Norwegian sling-system apparatus; the individual performs 3. The traditional method to evaluate gender differ- the down and up phases of the push-up movement while ences in muscle strength creates a ratio score for countering instability of the dual suspended ropes for the strength (i.e., strength per unit body mass, FFM, arms and legs. The idea is to maintain stability and balance limb volume, and girth). When considering meas- during the push-up, similar to a conventional push-up with ures of body size and/or composition in this manner, the hands and/or feet supported on a solid surface. (Photo the large strength differences between men and courtesy of Redcord, Kilsund, Norway.) women decrease considerably. 4. Allometric scaling offers another method to compare physiologic variables among individuals. 5. Optimal overload training to strengthen muscles involves three factors: (1) increasing resistance (load) to muscle action, (2) increasing speed of Slolow High muscle action, or (3) combining increased load Velocity Velocity and speed. Strength Strength 6. An overload between 60 and 80% of a muscle’s Window of force-generating capacity induces strength gains. Explosive Power 7. Three major strength-training systems include pro- Development gressive resistance weight training, isometrics, and isokinetic training. Each produces strength gains highly specific to the type of training. Isokinetic training offers potential to generate maximum force throughout the full ROM at different angular velocities of limb movement. 8. Closely supervised resistance training programs that use relatively moderate concentric muscle actions Rate of Inter-Inter- Force Stretch muscular improve children’s strength without adverse effects Develop- Shortening Coordination on bone, muscle, or connective tissue. Cycle ment and Skill 9. Periodization divides a distinct period or macrocycle of resistance training into smaller training mesocycles; these subdivide into weekly Figure 22.17 • Five components that contribute to explosive microcycles. Compartmentalization of training power development. Adapted with permission from Dr. minimizes staleness and overtraining effects to William J. Kraemer, Human Performance Laboratory, maximize peak performance that coincides with University of Connecticut. Storrrs, CT. (From Kraemer WJ, competition. Newton RU. Training for muscular power. Phys Med Rehabil 10. Resistance training for competitive athletes opti- Clin 2000;11:341.) mizes muscular strength, power, and hypertrophy. Training goals for middle-aged and older adults aim to modestly improve muscular strength and endurance, maintain muscle and bone mass, and Athletes must focus on training their least-developed compo- enhance overall health and fitness. nents. Stated somewhat differently, maximal power perform- 11. Concurrent training for muscular strength and aero- ance improves more readily when targeting specific training bic capacity inhibits the magnitude of strength im- routines to improve the weakest links because these have the provement compared with training only for largest adaptation window to develop explosive power. muscular strength. 97818_ch22.qxd 8/4/09 4:44 PM Page 519

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 519 12. Plyometric training emphasizes the inherent FACTORS THAT MODIFY THE stretchÐrecoil characteristics of the neuromuscular EXPRESSION OF HUMAN STRENGTH system to facilitate muscle power development. 13. Specificity of physiologic and performance mea- FIGURE 22.19 shows that factors broadly characterized as psy- sures and their response to training casts doubt on chologic (neural) and muscular influence the expression of the efficacy of general fitness measures to predict human strength. A resistance-training program modifies many ability to perform specific tasks or occupations. components of these factors; other factors remain training re- 14. Functional movement training via body weightÐ sistant, probably determined by natural endowment or estab- supported exercise offers a unique approach to lished early in life. sports training. 15. Core training remains an integral part of sports training and physical conditioning to improve Neural Adaptations with Resistance Training muscular balance, muscular strength, and trunk that Increase Muscular Strength stabilization. 1. Greater efficiency in neural recruitment patterns 2. Increased motor neuron excitability STRUCTURAL AND 3. Increased central nervous system activation Part 2 ¥ 4. Improved motor unit synchronization and in- FUNCTIONAL ADAPTATIONS creased firing rates TO RESISTANCE TRAINING 5. Lowering of neural inhibitory reflexes 6. Inhibition of Golgi tendon organs Muscle tissues exist in a dynamic state where proteins are al- ternately synthesized (net deposition of amino acids) and de- graded (net release of amino acids). FIGURE 22.18 lists six Psychologic–Neural Factors factors that develop and maintain muscle mass. Without a doubt, genetic factors provide the governing frame of refer- Adaptive alterations in nervous system function that elevate ence that modulates each of the other factors that increase motor neuron output largely account for the rapid and large muscle mass and strength.207 Muscular activity contributes strength increases early in training, often without an increase little to tissue growth without appropriate nutrition, particu- in muscle size and cross-sectional area.1,211 Neural adapta- larly amino acid availability, to provide essential building tions play a particularly important role in the dramatic muscu- blocks. Similarly, specific hormones (e.g., testosterone, lar strength and power improvements of the elderly with 90 growth hormone, cortisol, and, most importantly, insulin and resistance training. FIGURE 22.20 shows the generalized re- systemic and local insulin-like growth factors) and nervous sistance training response for neural facilitation and muscle system innervation help to pattern and reinforce the appropri- hypertrophy. ate training response. Without tension overload, each of the Research has considered the effects of exercise training other factors cannot effectively produce the desired training on structural changes associated with the neuromuscular response. junction (NMJ). In one study with rats, endurance training

Genetics Nervous Physical activity system activation

Nutritional Environmental status factors Endocrine influences

Figure 22.18 • Interaction of six factors that develops and maintains muscle mass. 97818_ch22.qxd 8/4/09 4:44 PM Page 520

520 Section 4 Enhancement of Energy Transfer Capacity

Steroids

Most Most serious training strength

studies athletes Progress

Training duration

Strength Neural Hypertrophy

Figure 22.19 • Relative roles of neural and muscular adaptations in strength improvement with resistance training. Note that neural adaptations predominate in the early phase of training (this phase encompasses the duration of most research studies). Hypertrophy-induced adaptations place the upper limit on longer term training improvements. This tempts many athletes to use anabolic steroids and/or human growth hormone (dashed line) to induce continual hypertrophy if training alone fails. (From Sale DG. Neural adaptation to resistance training. Med Sci Sports Exerc 1988;20:135.)

improved the ratio of nerve terminal area to muscle fiber size muscle cross section, fiber type, and mechanical arrangement by reducing fiber diameter without altering nerve terminal of bone and muscle, explain strength capacity. Neuromuscular size.266 In humans, high- and low-intensity training differen- inhibition can come from unpleasant past experiences with tially affected the size of the NMJ.61 Less intense, prolonged exercise, an overly protective home environment, or fear of workouts produced a more expansive NMJ area, whereas in- injury. Regardless of the reason, the person usually cannot ex- tense exercise produced greater dispersion of synapses. press maximum strength capacity. The excitement of intense A unique series of classic experiments illustrates the im- competition or influence of disinhibitory drugs or hypnotic portance of psychologic factors in expressing muscular suggestion often induces a “supermaximal” performance strength in humans.113 The researchers measured arm strength from greatly reduced neural inhibition and optimal motor in college-aged men under (1) normal conditions, (2) immedi- neuron recruitment. ately after a loud noise, (3) while the subject screamed loudly Highly trained athletes often create an almost self- at the time of exertion, (4) under the influence of alcohol and hypnotic state by intensely concentrating, or “psyching,” be- amphetamines (“pep pills”), (5) and under hypnosis (told they fore competition. It sometimes takes years of training to perfect possessed considerable strength and should not fear injury). the “block out” of extraneous stimuli (e.g., crowd noise) so the Each of the alterations generally increased strength above muscle action relates directly to the performance. This practice normal levels; hypnosis, the most “mental” of all treatments, has been perfected in powerlifting competition where success produced the greatest increments. depends on precise, coordinated movements with maximal The investigators theorized that temporary modifications muscle tension output. Enhanced arousal level and accompany- in central nervous system function accounted for strength im- ing neural disinhibition (or facilitation) fully activate muscle provements under the various experimental treatments. They groups. Increased neurologic arousal also may account for “un- argued that most persons normally operate at a level of neural explainable” feats of strength and power during highly charged inhibition, perhaps via protective reflex mechanisms that emergency and rescue situations (e.g., a relatively small person constrain the expression of strength capacity. Three factors, lifting an extremely heavy object off an injured person). 97818_ch22.qxd 8/4/09 4:44 PM Page 521

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 521

TABLE 22.5 • Physiologic Adaptations 100 to Resistance Training System/Variable Response

80 Muscle fibers Number Equivocal Size Increase Type Unknown Strength Increase 60 Capillary density In bodybuilders No change In power lifters Decrease Mitochondria 40 Volume Decrease Density Decrease Twitch contraction time Decrease Enzymes 20 Creatine phosphokinase Increase g e contribution to stren th improvement Myokinase Increase Enzymes of glycolysis Phosphofructokinase Increase 0 024 6 8 10 Lactate dehydrogenase No change Percenta Training duration (wk) Aerobic metabolism enzymes Carbohydrate Increase Triglyceride Not known Neural Hypertrophic Basal metabolism Increase Intramuscular fuel stores Figure 22.20 • Generalized response curve for gains in Adenosine triphosphate Increase muscle strength with resistance training from neural (orange) Phosphocreatine Increase or muscular (yellow) factors. During a typical 8-week training Glycogen Increase Triglycerides Not known period, neural factors account for approximately 90% of the и strength gained over the first 2 weeks. In the subsequent 2 VO2max weeks, between 40 and 50% of the strength improvement Circuit resistance training Increase still relates to nervous system adaptation. Thereafter, muscle Heavy resistance training No change fiber adaptations become progressively more important to Connective tissue strength improvement. Experiments of this type generally Ligament strength Increase evaluate neural factors from integrated EMG recordings of Tendon strength Increase Collagen content of muscle No change the muscle groups trained. Body composition Percent body fat Decrease Muscular Factors Lean body mass Increase Psychologic disinhibition and learning factors greatly modify Bone muscle strength in the early phase of training. Ultimately, Mineral content and density Increase Cross-sectional area No change anatomic and physiologic factors within the jointÐmuscle unit determine strength capacity. TABLE 22.5 lists the physiologic Modified from Fleck SJ, Kraemer WJ. Resistance training: physiological and performance changes associated with long-term resist- responses and adaptations (part 2 of 4). Phys Sportsmed 1988;16:108. ance training. Most of these components adapt to training, with some modifications occurring within several weeks. Resistance training’s effects on muscle fibers generally relate cross-sectional area. Two fundamental adaptations necessary to adaptations in the contractile structures; these usually ac- for muscle hypertrophy (increased protein synthesis and satel- company substantial increases in muscular force and power lite cell proliferation) are mobilized from the initial phases of through a given ROM. resistance training.220,286 Mechanical stress on components of the muscular system triggers signaling proteins to activate genes that activate translation of messenger RNA and stimu- Muscle Hypertrophy late protein synthesis in excess of protein breakdown. An increase in muscular tension (force) with exercise Accelerated protein synthesis, particularly when combined training provides the primary stimulus to initiate the process with the effects of insulin and adequate amino acid availabil- of skeletal muscle growth or hypertrophy. Changes in muscle ity, increases muscle size during resistance training.131 Muscle size become detectable after only three weeks of training, and hypertrophy reflects a fundamental biologic adaptation to the remodeling of muscle architecture precedes gains in muscle increased workload independent of gender and age. 97818_ch22.qxd 8/4/09 4:44 PM Page 522

522 Section 4 Enhancement of Energy Transfer Capacity As mentioned previously, improving muscular strength and power does not necessarily require muscle fiber hypertrophy because important neurologic factors initially affect the expression of human strength. The later, slower occurring strength improvements generally coincide with noticeable alterations in a muscle’s subcellular molecular architecture. Overload training enlarges individual muscle fibers with subsequent muscle growth. The fast-twitch fibers of weightlifters average about 45% larger than fibers of healthy sedentary persons and endurance athletes. The hypertrophic process couples directly to increased mononuclear number A and synthesis of cellular components, particularly protein filaments (myosin heavy chain and actin) that constitute the contractile elements.18,96 Resistance exercise creates more efficient translation of mRNA that mediates stimulation of myofibrillar protein synthesis.273 Muscle growth occurs from repeated muscle fiber injury (particularly with eccentric actions) followed by overcompensation of protein synthesis to produce a net anabolic effect. The cell’s myofibrils thicken and increase in number, and additional sarcomeres form from accelerated protein synthesis and corresponding decreased protein breakdown. Intramuscular ATP, PCr, and glycogen also increase considerably. These anaerobic energy stores B Control Hypertrophy contribute to the rapid energy transfer required in resistance training. Body-build characteristics also help to explain individual differences in responsiveness to resistance training. Figure 22.21 • A. Control (left) and hypertrophied (right) rat The greatest increases in muscle mass occur for individuals soleus muscle. B. Cross sections of control and hypertrophied with the largest relative FFM (corrected for stature and body muscles shown in A. The average diameter for 50 fibers of the fat before training begins).261 hypertrophied muscle was 24 to 34% greater than for FIGURE 22.21 shows the change in muscle fiber size that controls; the average number of nuclei in hypertrophied accompanies exercise-induced hypertrophy. Figure 22.21A muscle averaged 40 to 52% greater than controls. (From (left) compares exercised and nonexercised rat soleus muscle. Goldberg AL, et al. Mechanism of work-induced hypertrophy of skeletal muscle. Med Sci Sports 1975;3:185.) The hypertrophied exercised muscle appears on the right. Figure 22.21B represents a typical cross section of untrained and hypertrophied muscles. Hypertrophied muscle diameter The absence of these factors decreases the ratio of mito- averages 30% larger and the fibers contain 45% more nuclei, chondrial volume and/or enzyme concentration to myofibril- which increase relative to fiber size. These compensatory lar (contractile protein) volume. This training response does changes relate to marked increases in DNA synthesis and pro- not hinder performance in strength and power activities be- liferation of connective tissue cells and small, mononucleated cause of the anaerobic nature of such efforts. It does, how- satellite cells located beneath the basement membrane adja- ever, impede endurance in prolonged exercise by reducing the cent to the muscle fibers. These satellite cells, rich among type fiber’s aerobic capacity per unit of muscle mass. II muscle fibers, facilitate growth, maintenance, and repair of 91,98 damaged muscle tissue. Connective tissue cellular prolif- Specificity of the Hypertrophic Response eration thickens and strengthens the muscle’s connective tissue harness to improve the structural and functional integrity One should not assume that a single resistance exercise of tendons and ligaments (cartilage lacks sufficient circulation creates uniform strength improvement or the hypertrophic to stimulate growth).136 Such adaptations protect joints and response in the muscle(s) activated.8 For example, bicep muscles from injury. These adaptations justify including re- curls performed at close to 1-RM do not produce equal sistance exercise in preventive and rehabilitative orthopedic strength gains from the muscle’s origin to its insertion. If programs (see “Focus on Research,” Chapter 18, p. 356). they did, then the maximal force-generating capacity of the Resistance-trained muscle fibers have increased total muscle would show similar percentage improvements contractile protein and energy-generating compounds without throughout its ROM. This does not occur. Similarly, electri- the following components: cal activity measured by surface or needle EMG or MRI to assess a muscle’s cross-sectional area does not produce a 1. Parallel increases in capillarization homogeneous response within the entire muscle during max- 2. Total volume of mitochondria imal activation.31,175,215 A single muscle compartmentalizes 3. Mitochondrial enzymes into distinct regions. This indicates that the muscle’s different 97818_ch22.qxd 8/4/09 4:44 PM Page 523

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 523 areas respond differentially to the imposed adaptive stress. In essence, skeletal muscle remodels its internal architecture, potentially reconfiguring external orientation and hence its 2.0

shape. The overall lack of homogeneity in skeletal muscle’s response to overload, coupled with intramuscular differences 1.8 in fiber type and composition, governs the training adapta- 1.6

tion to specific resistance exercise. ast- to slow- f

g 1.4 Significant Metabolic Adaptations Occur 1.2 Elite sport performance success requires optimization of mus- twitch f iber area cle fiber distribution. The relatively fixed nature of muscle fiber Posttrainin 1.0 type suggests an obvious genetic predisposition for exceptional performance. Considerable plasticity exists for metabolic 1.0 1.2 1.4 1.6 1.8 2.0 potential because specific training enhances the anaerobic and Pretraining fast- to slow-twitch fiber area aerobic energy transfer capacity of both fiber types. The heightened oxidative capacity of fast-twitch fibers Posttraining average Pretraining average with endurance training brings them to a level nearly equal to the aerobic capacity of the slow-twitch fibers of untrained Figure 22.22 • Individual changes for 14 men in the ratio of counterparts. Endurance training induces some conversion of fast- to slow-twitch muscle fiber area after 8 weeks of type IIb fibers to the more aerobic type IIa fibers.283 The well- resistance training. Orange circle on right indicates average documented increase in mitochondrial size and number, and pretraining FT:ST area ratio; yellow circle represents the corresponding increase in total quantity of citric acid cycle and posttraining average. (From Thorstensson A. Muscle strength, electron transport enzymes, accompanies these fiber subdivi- fiber types, and enzyme activities in man. Acta Physiol Scand sion changes. Only the specifically trained muscle fibers adapt Suppl 1976:443.) to regular exercise; this helps to explain why trained athletes who change to a sport that requires different muscle groups (or activation of a much greater proportion of one fiber type than different portions of the same muscle) often feel untrained. another. Within this framework, swimmers or canoeists (with well- trained upper-body musculature) do not necessarily transfer Muscle Cell Remodeling: Current Thinking upper-body fitness to a running sport that relies predominantly on a highly conditioned lower-body musculature. Skeletal muscles represent dynamic tissues whose cells Metabolic characteristics of specific fibers and fiber sub- do not remain as fixed populations throughout life. Rather, divisions undergo modification within 4 to 8 weeks of tar- muscle fibers undergo regeneration and remodeling to diverse geted resistance training. This occurs despite the lack of functional demands (e.g., resistance or endurance training) to dramatic changes in inherent muscle fiber type. A decrease in alter their phenotypic profile.99 Activation of muscle via spe- the percentage of type IIx and corresponding increase in cific types and intensities of long-term use stimulates other- type IIa fibers denotes one of the more prominent and rapid wise dormant myogenic stem cells (satellite cells) situated training adaptations.5 Furthermore, the volume of the trained under a muscle fiber’s basement membrane to proliferate and fast-twitch fibers increases. FIGURE 22.22 clearly illustrates this differentiate to form new fibers. Fusion of satellite cell nuclei increase for the relative areas of the fast- and slow-twitch and incorporation into existing muscle fibers allow the fiber muscle fibers before and after training. Considerable hyper- to synthesize more protein to form additional myofibril con- trophy, predominantly of the fast-twitch fibers, occurs in tractile elements. Although this process does not create new power and Olympic-type lifters who train diligently over muscle fibers per se, it does contribute directly to muscular many years with progressive resistance training.243,245 This hypertrophy and may stimulate transformation of existing makes sense within the framework of exercise specificity be- fibers from one type to another. cause near-maximal resistance exercise that requires high lev- A variety of extracellular signal molecules, primarily els of anaerobic power primarily recruits fast-twitch motor peptide growth factors (e.g., insulin-like growth factor [IGF], units. Resistance training also improves glucose transport in fibroblast growth factors, transforming growth factors, and normal and insulin-resistant skeletal muscle by enhancing ac- hepatocyte growth factor) govern satellite cell activity and tivation of the insulin signaling cascade and increasing possibly exercise-induced muscle fiber proliferation and dif- GLUT-4 protein concentration. These training-induced alter- ferentiation. FIGURE 22.23 proposes a model for muscle cell re- ations improve the quality of the skeletal muscle and occur in- modeling that involves satellite cell incorporation into an dependent of increases in skeletal muscle mass.284 existing muscle fiber. A specific set of genes (gene A in the TABLE 22.6 summarizes changes in skeletal muscle with figure) is expressed in the fiber’s preexisting nuclei. Chronic specific training modalities. Generally, physical activity activation from physical activity stimulates satellite cell pro- recruits both fiber types; however, certain activities require liferation, with some cells differentiating and fusing with 97818_ch22.qxd 8/4/09 4:44 PM Page 524

524 Section 4 Enhancement of Energy Transfer Capacity

TABLE 22.6 • Effects of Specific Types or Training on Skeletal Muscle Slow-Twitch Fibers Fast-Twitch Fibers

Type of Training Muscle Factor Strength Endurance Strength Endurance

Percentage composition 0 or ? 0 or ? 0 or ? 0 or ? Size ϩ 0 or ϩϩϩ 0 Contractile property 0000 Oxidative capacity 0 ϩϩ 0 ϩ Anaerobic capacity ? or ϩ 0 ? or ϩ 0 Glycogen content 0 ϩϩ 0 ϩϩ Fat oxidation 0 ϩϩ 0 ϩ Capillary density ? ϩ ? ? or ϩ Blood flow during exercise ? ? or ϩ ??

0, no change; ?, unknown; +, moderate increase; ++, large increase.

preexisting muscle fibers. The new muscle nuclei alter gene rapid, high-power periodized resistance-training program.184 expression (gene B in the figure) in the adapting muscle. Preserving muscle structure and function as one ages may Muscle fiber-type transformation may occur with spe- provide a physical reserve capacity above the critical thresh- cific exercise training. In one study, four athletes trained old required for independent living at old age.2,282 anaerobically for 11 weeks followed by 18 weeks of aero- Equally impressive training responses occur for persons bic training. Anaerobic training increased the percentage of 80 years and older. One hundred nursing home residents type IIc fibers (a previous subclassification) and decreased (average age 87.1 y) trained for 10 weeks with high-intensity re- the percentage of type I fibers; the opposite occurred during sistance exercise.72 For the 63 women and 37 men who partici- the aerobic training phase.123 Similarly, 4 to 6 weeks of pated, muscle strength increased an average of 113%. Strength sprint training increased the percentage of fast-twitch increases also paralleled improved function, reflected by an fibers, with a commensurate decrease in slow-twitch fiber 11.8% increase in normal gait velocity and 28.4% increase in percentage.58 Increasing daily training duration also in- stair-climbing speed; thigh muscle cross-sectional area increases the fast- to slow-twitch shift in myosin heavy-chain creased by 2.7%. Other studies also have verified the benefits of phenotype in rat hind limb muscles.60 Specific training (and functional strength training to improve activities of daily living perhaps inactivity) may convert different physiologic char- (ADL), including countering the devastating medical conse- acteristics of type I to type II fibers (and vice versa).224,243 quences of slips and falls in the older elderly.33,224,243 Available evidence does not permit definitive statements concerning the fixed nature of a muscle’s fiber composi- Muscle Hyperplasia: Are New tion. The genetic code more than likely exerts the greatest Muscle Fibers Made? influence on fiber-type distribution. The major direction of a muscle’s fiber composition probably becomes fixed be- A common question concerns whether training increases fore birth or during the first few years of life. the number of muscle cells (hyperplasia). If this does occur, to what extent does it contribute to muscle enlargement in humans? Chronic overload of skeletal muscle in various animal Benefits Regardless of Gender or Age species stimulates new muscle fiber development from satel- Muscles and tendons, highly adaptable tissues, respond lite cells or by longitudinal splitting.11 Under conditions of favorably to chronic changes in loading independent of age or (1) stress, (2) neuromuscular disease, and (3) muscle injury, gender.13,140,141,180,205 A study of five active, older, healthy men the normally dormant satellite cells develop into new muscle (average age 68 y) demonstrates the remarkable plasticity of fibers (see Fig. 22.23). With longitudinal splitting, a rela- human skeletal muscle (FIG. 22.24). The men trained for tively large muscle fiber splits into two or more smaller, indi- 12 weeks using heavy-resistance isokinetic and free-weight ex- vidual daughter cells through lateral budding. These fibers ercises. Training increased muscle volume and cross-sectional function more efficiently than the large single fiber from area of the biceps brachii (13.9%) and brachialis (26.0%), which they originated.12 while hypertrophy increased by 37.2% in the type II muscle Generalizing findings from research on animals to hu- fibers. Increases of 46.0% in peak torque and 28.6% in total mans poses a problem. The massive cellular hypertrophy work output accompanied cellular adaptations. Similarly, observed in humans with resistance training does not occur in older men experience percentage improvements in these many animal species. In cats, for example, muscle fiber prolif- variables similar to younger counterparts in response to a eration (hyperplasia) often reflects the primary compensatory 97818_ch22.qxd 8/4/09 4:44 PM Page 525

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 525

Neuromuscular activities

New nucleus

Preexisting mRNA B nucleus mRNA A

Gene B Gene A Protein A Protein B

Satellite cell

Proliferation

Differentiation

Figure 22.23 • A model for skeletal muscle adaptation that involves satellite cells. A specific set of genes (gene A) is expressed in the preexisting myonuclei. Upon stimulation from increased neuromuscular activity, the satellite cells proliferate, and some of them differentiate and fuse with the preexisting myofibers. These myonuclei may alter gene expression (gene B) in the adapting muscle because they undergo altered differentiation from increased neuromuscular activities. (From Yan Z. Skeletal muscle adaptation and cell cycle regulation. Exerc Sport Sci Rev 2000;1:24.)

adjustment to overload. Some evidence supporting hyperplasia “hypertrophied” to normal size with resistance training), yet in humans does exist. For example, autopsy data from young, the findings suggest hyperplasia with certain modes of resist- healthy men who died accidentally show that muscle fiber ance training. Muscle fibers may adapt differently to the high- counts of the larger and stronger leg (leg opposite the domi- volume, high-intensity training practiced by bodybuilders than nant hand) contained 10% more muscle fibers than the the typical low-repetition, heavy-load system favored by smaller leg.225 Cross-sectional studies of bodybuilders with strength and power athletes. Even if other human studies repli- relatively large limb circumferences and muscle masses cate a training-induced hyperplasia (and even if the response failed to show they possessed above-normal size individual reflects a positive adjustment), enlargement of existing indi- muscle fibers.159,160,244 Some of the bodybuilders may have vidual muscle fibers represents the greatest contribution to in- inherited an initially large number of small muscle fibers (that creased muscle size from overload training. 97818_ch22.qxd 8/4/09 4:44 PM Page 526

526 Section 4 Enhancement of Energy Transfer Capacity Changes in Muscle Fiber Type with Resistance Training 50 Research has evaluated the effects of 8 weeks of resistance exercise on muscle fiber size and fiber composition for the 40 leg extensor muscles of 14 men who performed three sets of 6- 247 f t-lb) RM leg squats three times weekly. Biopsy specimens from 30 the vastus lateralis muscle before and after training showed no change with resistance training in percentage distribution of 20 fast- and slow-twitch muscle fibers. This finding agreed with previous short-term resistance and endurance-type training 10

Peak torque ( Peak studies and indicates that several months of resistance training in adults does not alter the basic fiber composition of skeletal 0 muscle. It remains unclear whether specific training early in 60 120 180 240 300 life or for prolonged durations practiced by elite athletes alters . –1 Velocity (degrees s ) a muscle fiber’s inherent twitch (speed of shortening) charac- )

2 40 teristics. Some progressive fiber-type transformation may occur with longer duration, specific training (see Chapter 18). Current thinking posits that genetic factors largely determine 30 one’s predominant muscle fiber type distribution.

20 COMPARATIVE TRAINING RESPONSES IN MEN AND WOMEN In today’s society, women participate successfully in all sports 10 and physical activities. Women generally had not incorporated resistance training during workouts, to avoid developing overly enlarged muscles similar to men. This hesitation was unfortu- 0

Muscle cross-sectional area (cm 510152025 nate because specific strength acquisition enhances perform- Muscle slice (cm) ance in tennis, golf, skiing, dance, gymnastics, and most other sports including physically demanding occupations such as firefighting and construction work. The question often arises 8000 whether muscular strength acquisition differs between men and ) 2 women, and if so, what factors might be responsible?

6000 INTEGRATIVE QUESTION 4000 If women respond to resistance training essentially the same way as men, explain the 2000 disparity between the upper-arm girth of male and female bodybuilders. Muscle f iber area (μm 0 Type I Type II Muscle fiber type Muscular Strength and Hypertrophy Pre Post The absolute amount of muscle hypertrophy with resistance Figure 22.24 • Plasticity of aging muscle. Data from five training represents a primary gender difference. Computed men, 68 years of age, before (orange) and after (yellow) 12 axial tomography (CAT) scans for direct evaluation of muscle weeks of heavy-resistance training. Top. Peak torque of elbow cross-sectional area show that men and women respond simi- flexors. Middle. Plot of flexor cross-sectional area computed larly in hypertrophic response to resistance training. Without from MRI scans from proximal (right) to distal (left) end of doubt, men experience a greater absolute change in muscle size muscle. Bottom. Average for type I and type II fiber areas. because of their larger initial muscle mass, but muscular en- (From Roman WJ, et al. Adaptations in the elbow flexors of largement on a percentage basis remains similar between gen- elderly males after heavy-resistance training. J Appl Physiol ders.55,108,193,269 Comparisons between elite male and female 1993;74:750.) bodybuilders also indicate substantial muscular hypertrophy in females with many years of resistance training.231,232 97818_ch22.qxd 8/4/09 4:44 PM Page 527

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 527 Gender-related differences in hormonal response to resistance exercise (e.g., increased testosterone and decreased cortisol for men) may determine any ultimate gender differences in muscle size and strength adaptations with prolonged training. This intriguing area requires longitudinal research for a richer description of gender differences in how skeletal Normal BMD muscle responds to resistance training.

Does Muscle Strength Relate to Bone Density? A positive relationship exists between muscular strength and Low BMD bone mineral density.57,164 Men and women who participate in strength and power activities have as much or more bone mass than endurance athletes.210,216,262 The lumbar spine and 0 50 100 150 200 proximal femur bone mass of elite teenage weightlifters49 and Torque (N-m) in adolescent boys and girls271 exceed representative values for fully mature bone of reference adults. A linear relation exists between increases in bone min- Flexion Extension eral density (BMD) and total and exercise-specific weight lifted during a 1-year strength-training program.56 Such Figure 22.25 • Comparison of chest press extension findings have raised speculation about the possible positive and flexion strength in age- and weight-matched postmenopausal women with normal and low bone mineral relationship between muscular strength and bone mass. density (BMD). Women with low BMD scored significantly Laboratory experiments have documented greater maximum lower on each measure of muscular strength than a reference flexion and extension dynamic strength in postmenopausal group. (From Stock JL, et al. Dynamic muscle strength is women without osteoporosis than in osteoporetic counter- decreased in postmenopausal women with low bone density. parts.236 For female gymnasts, BMD correlated moderately J Bone Miner Res 1987;2:338; Janey C, et al. Maximum with maximal muscle strength and serum progesterone.103 muscular strength differs in postmenopausal women with For adolescent female athletes, absolute knee extension and without osteoporosis. Med Sci Sports Exerc strength moderately associated with total body, lumbar spine, 1987;19:S61.) 66 femoral neck, and leg BMD. FIGURE 22.25 shows chest flex- 6.4% of their type II muscle fiber area, without loss in type I ion and extension strength in normal and osteoporotic 105 women. Women with normal BMD (measured by dual- fiber area. Abstaining for a short period of resistance photon absorptiometry in the lumbar spine and femur neck) training in previously sedentary men caused loss of strength gains within several weeks, most likely from reversal of train- exhibited 20% greater strength in 11 of 12 test comparisons 47 for flexion; 4 of 12 comparisons for extension showed 13% ing-induced neuromuscular and hormonal adaptations. higher strength values for women with normal bone density. Reducing training frequency to only one or two weekly sessions provides sufficient stimulus to maintain training- Subsequent data complement these findings; they indicate 85 that regional lean tissue mass (often an indication of muscu- induced strength gains. lar strength) accurately predicts bone mineral density.185 Differences in maximum dynamic strength among post- METABOLIC STRESS OF menopausal women may serve a clinically useful role in os- RESISTANCE TRAINING teoporosis screening. Women at risk for osteoporosis or with osteoporosis can High-intensity, variable-resistanceи strength training produces attenuate their factor of risk (ratio of the load on bone to the no improvement in VO2max or submaximal exercise heart rate 111 bone’s failure load) for fracture in one of two ways178: and stroke volume. Lack of cardiovascular improvement with standard resistance training probably results from the 1. Strengthen bone by increasing bone density relatively low “whole body” metabolic and circulatory de- 2. Avoid risky activities that increase bone load or mands and high anaerobic metabolic requirements of such spinal compression (e.g., heavy lifting activities) training. This is reflected by the potent stimulation of glucose uptake and lactate release by the active muscle.67 Data from young men during maximal isometric and 8- to 10-RM DETRAINING weightlifting exercises indicate that such activity elicits Limited data document muscle strength decrements and only light-to-moderate heart rate response (generally less than Ϫ associated factors with cessation of resistance training. 130 b и min 1) and oxygen consumption (3 to 4 METs).166 Discontinuing training for 2 weeks caused male power lifters Undoubtedly, resistance training places considerable lo- to lose 12% of their isokinetic eccentric muscle strength and calized stress on specific muscles. The brief activation period 97818_ch22.qxd 8/4/09 4:45 PM Page 528

528 Section 4 Enhancement of Energy Transfer Capacity and typically small muscle mass activated in such exercise creates lower heart rates and aerobic metabolic demands than TABLE 22.7 • Energy Expenditure for Different dynamic big-muscle running, hiking, climbing, swimming, or Modes of Resistance Exercise a cycling. A person may devote an hour or more to complete a Compared with Walking strength-training workout, yet the total time devoted to exer- Mode Sex kJ и min–1 kCal и min–1 cising does not usually exceed 8 minutes per hour. Clearly, traditional resistance-training workouts should not constitute Nautilus, circuit M 29.7 7.1 the major portion of a program designed for cardiovascular F 24.3 5.8 improvement and weight control. Nautilus, circuit M 22.6 5.4 Universal, circuit M 33.1 7.9 CIRCUIT RESISTANCE TRAINING F 28.5 6.8 Isokinetic, slow M 40.2 9.6 Modifying the traditional approach to resistance training Isokinetic, fast M 41.4 9.9 increases the caloric cost of exercise to improve several im- Isometric and portant fitness aspects. Circuit resistance training (CRT) free-weight M 25.1 6.0 deemphasizes the brief intervals of heavy, local-muscle over- Hydra-Fitness, circuit M 37.7 9.0 load in standard resistance training. It provides more-general Walking on level M 22.6 5.4 conditioning that improves body composition, muscular strength and endurance, and cardiovascular fitness.8,80 With Data from Katch FI, et al. Evaluation of acute cardiorespiratory responses to hydraulic resistance exercise. Med Sci Sports Exerc 1985;17:168. CRT, a person lifts a weight between 40 and 55% of 1-RM as aBased on a body weight of 68 kg. many times as possible with good form for 30 seconds. After a 15-second rest, the participant moves to the next resistance exercise station and so on to complete the circuit, usually Energy Cost of Different composed of 8 to 15 different exercises. A modification that Resistance-Exercise Methods produces similar CRT energy expenditure uses exercise-to- TABLE 22.7 displays energy expenditures for exercise per- rest ratios of 1:1, with either 15- or 30-second exercise peri- formed using free weights, Nautilus (eccentric), Universal ods.19 The circuit repeated several times allows for 30 to 50 Gym (concentric/eccentric), Cybex (isokinetic), and Hydra- minutes of continuous exercise, not just the 6 to 8 minutes of Fitness (hydraulic-concentric). Energy expenditure for hy- the traditional resistance-training workout. As strength in- draulic exercises averaged 9.0 kCal и minϪ1; this averaged creases, a new 1-RM determined for each exercise provides 35% higher than exercise with free weights, 29.4% higher the basis to increasing the resistance. than Nautilus exercise, and 11.5% more than CRT using The CRT modification of standard resistance training Universal Gym equipment. The energy expenditure values for offers an attractive alternative to those who desire a more gen- hydraulic exercise averaged about 6.4% less than slow- and eral conditioning program. Medically supervised CRT pro- fast-speed isokinetic circuit exercise. For comparison, the last grams effectively train coronary-prone, cardiac, and spinal line lists the energy expenditure for walking at a normal pace cordÐinjured patients for a well-rounded fitness program. CRT on a level surface. supplements off-season conditioning for sports that require high levels of strength, power, and muscular endurance. MUSCLE SORENESS AND STIFFNESS Specificity of Aerobic Improvement Following an extended layoff from exercise, or performing un- with CRT accustomed exercise, most persons experience soreness and stiffness in the exercised joints and muscles. Temporary sore- Some research indicates that CRT produces nearly 50% less ness may persist for several hours immediately after such unac- aerobic fitness improvement than bicycle or run training.79 customed exercise, whereas residual delayed-onset muscle Importantly, CRT usually involves substantial upper-body ex- soreness (DOMS) appears later and can last for 3 or 4 days. ercise, but assessment of aerobic benefits from this training Any one of the following seven factors may produce DOMS: relied on treadmill or bicycle tests that predominantly activate lower-body musculature. To compensate for this limitation, 1. Minute tears in muscle tissue or damage to its con- one study assessed CRT effects on aerobic capacity with tractile components with accompanying release of treadmill running and arm-crank ergometry tests.94 Aerobic creatine kinase (CK), myoglobin (Mb), and troponin capacity increased about 8% with treadmill testing and 21% I, the muscle-specific marker of muscle fiber damage with arm-crank testing, thus confirming the training speci- 2. Osmotic pressure changes that produce fluid reten- ficity principle. These findings take on added significance be- tion in the surrounding tissues cause they occurred without negative effects in a group of 3. Muscle spasms borderline hypertensives. The program also increased muscu- 4. Overstretching and tearing of portions of the mus- lar strength, decreased blood pressure, and modestly im- cle’s connective tissue harness proved body composition. 5. Acute inflammation 97818_ch22.qxd 8/4/09 4:45 PM Page 529

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 529 6. Alteration in the cell’s mechanism for calcium concentric and eccentric muscle actions. Group 1 performed regulation three sets of eight exercises (concentricÐeccentric) at 60% 7. Combination of the above factors of 1-RM on Universal Gym equipment: One set equaled 20 seconds of exercise followed by 40 seconds of rest; total Eccentric Actions Produce Muscle Soreness exercise time was 24 minutes. Group 2 followed the same exercise protocol, but they exercised maximally for each The precise cause of muscle soreness remains unknown, al- repetition on resistance devices powered by hydraulic cylin- though the degree of discomfort, muscle disturbance, and loss of ders that produced concentric-only actions. Blood samples strength depends largely on the intensity and duration of effort and ratings of perceived muscle soreness took place before and type of exercise performed.89,107,112,119,200 The magnitude of exercise and 5, 10, and 25 hours after exercise. The major active strain imposed on a muscle fiber (rather than absolute difference in soreness ratings between exercise groups oc- force) precipitates muscle damage and soreness.153 Eccentric curred 25 hours postexercise; the concentricÐeccentric muscle actions trigger the greatest postexercise discomfort, par- workout produced higher perceived ratings of soreness for ticularly magnified in older individuals.25,227,267 Existing muscle the major muscle groups exercised. The magnitude of in- damage or soreness from previous exercise does not exacerbate crease in serum CK remained the same between groups from subsequent muscle damage or impair the repair process.188 5 to 25 hours postexercise. Both exercise modes elevated In one study, subjects rated muscle soreness immediately serum CK, but the concentric-only muscle actions did not after exercise and 24, 48, and 72 hours later. Greater soreness cause DOMS. occurred from exercise that involved repeated intense strain during active lengthening in eccentric actions than from con- Cell Damage centric and isometric actions. Soreness did not relate to lactate buildup because high-intensity, level running (concentric ac- Running downhill at a 10¡ slope for 30 minutes produced tions) produced no residual soreness despite significant eleva- considerable DOMS 42 hours after exercise.34 Corresponding tions in blood lactate. In contrast, downhill running (eccentric increases also occurred in serum levels of Mb and the muscle- actions) caused moderate-to-severe DOMS without lactate el- specific enzyme CK, both common markers of muscle injury. evation during exercise. Acute inflammation also augments greater mobilization of TABLE 22.8 highlights muscle soreness and CK activity leukocytes and neutrophils. Subject testing also took place following an exercise circuit of either concentric-only or after 3, 6, and 9 weeks. FIGURE 22.26 shows the perceived

TABLE 22.8 • Acute Effects of Concentric-Only and Concentric–Eccentric Exercise on DOMS 25 Hours After Exercisea Soreness Ratings Soreness Ratings Concentric– Concentric– Concentric Eccentric Concentric Eccentric – – – – Site X X Site X X

Chest 2.3 5.1 Forearm (front) 1.7 3.4 Back (upper) 2.6 2.8 Forearm (back) 1.7 2.9 Shoulders (front) 2.2 3.6 Back (lower) 1.7 2.9 Shoulders (back) 1.9 3.6 Buttocks 1.8 2.5 Biceps (mid) 1.9 4.3 Quadricep (mid) 2.0 4.1 Biceps (lower) 1.8 3.5 Quadricep (lower) 2.1 3.8 Triceps (mid) 1.9 3.4 Hamstrings (mid) 2.1 3.5 Triceps (lower) 1.9 3.0 Hamstrings (lower) 2.1 3.0

؊ CK Activity (mU и mL 1) Sample Time Concentric Concentric–Eccentric – – X X

Pre 86.7 126.9 5 h post 344.8 232.0 10 h post 394.3 368.5 25 h post 288.0 482.2

From Byrnes WC. Muscle soreness following resistance exercise with and without eccentric muscle actions. Res Q Exerc Sport 1985;56:283. aAll differences between groups were statistically significant. XÐ ϭ mean 97818_ch22.qxd 8/4/09 4:45 PM Page 530

530 Section 4 Enhancement of Energy Transfer Capacity soreness rating for the leg muscles related to elapsed postexercise time for the three study durations. For the 3- and 10 6-week comparisons, differences between exercise bouts Three weeks reached statistical significance, with diminished DOMS noted g 8 in the second trial (orange). Similar patterns emerged for perception of muscle soreness and CK and Mb levels. Interestingly, peak soreness ratings at 48 hours did not relate 6 to absolute or relative CK or Mb changes. Individuals who reported the greatest DOMS did not necessarily have the high- 4 est CK and Mb values. The first bout of repetitive, high-force exercise probably disrupts the integrity of the sarcolemma to hest soreness ratin 2 produce mitochondrial swelling and temporary ultrastructural

Hi g muscle damage in a pool of stress-susceptible or degenerating muscle fibers. This response occurs with an increase in blood 0 Pre 8 16 48 markers such as protein carbonyls that reflect oxidative stress.147 10 The early mechanical damage to the myocytes (reflected by increased CK release) 24 hours postexercise does coincide Six weeks 29

g with acute inflammatory cell infiltration within the muscle. 8 The subsequent decrease in muscle performance for several days following eccentric injury primarily stems from failure 6 in excitationÐcontraction coupling and increased myofibrillar proteolysis.115,277 The fast-twitch fibers with low oxidative capacities show particular vulnerability, with more extensive 4 damage several days after exercise than in the immediate postexercise period. A single exercise bout protects against mus-

g hest soreness ratin 2 cle soreness and decrements in muscle strength in subsequent Hi exercise, with the effect lasting up to 6 weeks. Resistance to muscle damage in succeeding exercise may result from an ec- 0 Pre 8 16 48 centric exerciseÐinduced increase in muscle fiber sarcomeres connected in series.158 Such adaptations support the wisdom 10 of initiating a training program with light exercise to protect Nine weeks against the muscle soreness that almost always follows an initial intense exercise bout that includes an eccentric compo- 8 nent.78 Intense concentric exercise performed just prior to strenuous eccentric exercise does not magnify muscle dam- 6 age. It may prepare the muscle to respond more effectively to the next eccentric exercise stress. Even prior lower-intensity 4 exercise of specific muscles does not fully protect from DOMS with more intense exercise.

g g hest soreness ratin 2

Hi Altered Sarcoplasmic Reticulum

0 Four factors produce major alterations in sarcoplasmic Pre 8 16 48 reticulum structure and function with unaccustomed exercise: Hours postexercise 1. Changes in pH 2. Changes in intramuscular high-energy phosphates Exercise bout 1 Exercise bout 2 3. Changes in ionic balance Figure 22.26 • Highest soreness rating before and 8, 16, 4. Changes in temperature and 48 hours after exercise bout 1 (yellow) and a subsequent These effects depress the rates of Ca2ϩ uptake and release exercise bout (bout 2, orange) performed either 3, 6, or 9 and increase free Ca2ϩ concentration as the mineral rapidly weeks later. CK and Mb showed similar results. (From moves into the cytosol of the damaged fibers. Intracellular Byrnes WC, et al. Delayed onset muscle soreness following 2ϩ repeated bouts of downhill running. J Appl Physiol Ca overload contributes to the autolytic process within 1985;59:710.) damaged muscle fibers that degrades the contractile and noncontractile structures. Topographical mapping techniques to investigate sensory and EMG outcomes of DOMS have 97818_ch22.qxd 8/4/09 4:45 PM Page 531

CHAPTER 22 Muscular Strength: Training Muscles to Become Stronger 531 been investigated 24 h and 48 h following eccentric exercise in lipid peroxidation) compared with placebo treatment.149 multiple locations of the quadriceps muscle. Greater DOMS Supplementation with 750 mg per day of phosphatidylserine occurred in the distal region of the quadriceps, indicating a for 10 days did not afford additional protection against DOMS greater tendency of this region to further injury following the and markers of muscle damage, inflammation, and oxidative 101 eccentric exercise along with reduced force capacity. stress that follow prolonged downhill running.134 Similarly, Vitamin E supplementation, and perhaps vitamin C and taking a protease supplement had no effect on the perception of selenium, protects against cellular membrane disruption and pain associated with DOMS or the blood markers of muscle enzyme loss following muscle damage from resistance exercise damage.21 At 48 h postexercise-induced DOMS, milk and 83,167 (see Chapter 2). Postexercise protein supplementation also milk-based proteinÐcarbohydrate supplementation attenuated may protect against muscle soreness in severely exercise- decreases in isokinetic muscle performance and increases in 73 stressed individuals. In contrast, supplementing daily with ei- CK and Mb.44 ther fish oil (high in omega-3 and omega-6 fatty acids) or isoflavones (soy isolate) for 30 days prior to and during the Current DOMS Model week of testing to reduce the inflammatory response produced no benefit to DOMS (strength, pain ratings, limb girth, and FIGURE 22.27 diagrams the probable steps in the develop- blood measures related to muscle damage, inflammation, and ment of DOMS and subsequent recuperation.

Unaccustomed exercise using eccentric muscle actions (downhill running, slowly lowering weights)

High muscle forces damage sarcolemma causing release of cytosolic enzymes and myoglobin

Damage to muscle contractile myofibrils and noncontractile structures

Metabolites (e.g.,calcium) accumulate to abnormal levels in the muscle cell to produce more cell damage and reduced force capacity

Delayed-onset muscle soreness, considered to result from inflammation, tenderness, pain

The inflammation process begins; the muscle cell heals; the adaptive process makes the muscle more resistant to damage from subsequent exercise

Figure 22.27 • Proposed sequence for delayed-onset muscle soreness following unaccustomed exercise. Cellular adaptations to short-term exercise provide enhanced resistance to subsequent damage and pain. 97818_ch22.qxd 8/4/09 4:45 PM Page 532

532 Section 4 Enhancement of Energy Transfer Capacity INTEGRATIVE QUESTION 11. Women at risk for osteoporosis (or with the disease) reduce fracture risk by increasing bone density and Respond to the following: “I run and work out avoiding activities that increase spinal compression with free weights regularly, yet every spring my and bone stress. muscles are sore a day or two after a few hours of 12. Conventional resistance training does not improve yard work.” aerobic fitness. These workouts do not affect weight loss because of their relatively low caloric cost. 13. Circuit resistance training, by using lower resist- Summary ance and higher repetitions, effectively combines 1. The size and type of muscle fibers and the anatomic the muscle-training benefits of resistance exercise lever arrangement of bone and muscle (physiologic with the cardiovascular, calorie-burning benefits of factors) largely govern the upper limit to human continuous dynamic exercise. muscular strength. 14. Eccentric muscle actions induce greater DOMS 2. Central nervous system influences activate the than concentric-only or isometric actions. Serum prime movers in a specific action to affect maximal markers of muscle damage (CK and Mb) increase force capacity. with each form of muscle action. 3. Six factors—genetic, exercise, nutritional, hor- 15. A single exercise bout protects against DOMS and monal, environmental, and neural—interact to regu- muscle damage from subsequent exercise. The pro- late skeletal muscle mass and corresponding tection mechanism supports the wisdom of pro- strength development with resistance training. gressing gradually (lower intensity; minimize 4. Three factors contribute to increased muscle eccentric actions) when beginning an exercise pro- strength with resistance training: (1) improved ca- gram that requires application of considerable mus- pacity for motor unit recruitment, (2) changes in cular force. motor neuron firing pattern efficiency, and (3) alter- 16. The body initiates a series of adaptive cellular ations within the muscle fibers’ contractile elements. events (basically an inflammation response) to un- 5. Muscular overload increases strength and selec- accustomed exercise that produces DOMS. tively stimulates muscle fiber hypertrophy. Muscle hypertrophy includes increased protein synthesis References are available online at with myofibrillar thickening, connective tissue cell http://thepoint.lww.com/mkk7e. proliferation, and an increase in the number of satellite cells around each fiber. 6. Muscle hypertrophy entails structural changes On the Internet within the contractile apparatus of individual fibers, particularly fast-twitch fibers and increased anaero- American College of Sports Medicine bic energy stores. www.acsm.org 7. The genetic code exerts the greatest influence on American Heart Association www.americanheart.org/ muscle fiber-type distribution; a muscle’s fiber composition is largely fixed before birth or during Centers for Disease Control and Prevention www.cdc.gov/ the first few years of life. American Association of Cardiovascular and Pulmonary 8. Human muscle fibers adapt to increased functional Rehabilitation demands via action of myogenic stem cells (satel- www.aacvpr.org/ lite cells) that proliferate and differentiate to re- Office of the Surgeon General model the muscle. www.surgeongeneral.gov/ 9. Relatively brief periods of resistance training gener- The Global Economic and Healthcare Burden of ate similar strength improvements (on a percentage Musculoskeletal Disease basis) for women and men. www.ota.org/downloads/bjdExecSum.pdf 10. Muscle weakness in the abdominal and lower lumbar Bureau of Labor Statistics back regions (core), including poor flexibility in the www.bls.gov/ lower back and legs, represent primary factors National Strength and Conditioning Association related to low back syndrome. Core muscle- www.nsca-lift.org/ strengthening, flexibility, and balance exercises effectively protect against and rehabilitate this condition. 97818_ch23.qxd 8/4/09 4:46 PM Page 533

CHAPTER 23 Special Aids to Exercise Training and Performances

CHAPTER OBJECTIVES

➤ Define ergogenic aids and outline possible mech- ➤ Outline the general trend for endogenous dehy- anisms for their purported effects droepiandrosterone (DHEA) production during a lifetime ➤ Outline the procedure for formulating a randomized, double-blind, placebo-controlled research ➤ Discuss the rationale for DHEA as an ergogenic study and give the benefits of such a design aid and its potential risks ➤ List the categories of substances currently banned ➤ Summarize the controversy about androstene- by the International Olympic Committee dione as a benign nutritional supplement or a harmful drug ➤ Give examples of substances and procedures with alleged ergogenic benefits ➤ Discuss the effects of oral supplements of amino acids, carbohydrate-protein, and carbohydrate on ➤ Discuss the mode of action of anabolic steroids, hormone secretion, resistance-training responsive- their effectiveness, and risks when used by males ness, and exercise performance and females ➤ Summarize the research findings about ergogenic ➤ Summarize ACSM’s “Position Stand on Use of benefits and risks of amphetamines, caffeine, buffer- Anabolic Steroids” ing solutions, chromium picolinate, L-carnitine, glut- ➤ Give positive and negative findings from research amine, and ␤-hydroxy-␤–methylbutyrate on animals of the effect of ␤ -adrenergic agonists 2 ➤ Describe the typical time course for red blood cell ➤ Discuss the medical use of human growth hor- reinfusion and the mechanism for ergogenic mone and potential dangers for healthy athletes effects on endurance performance and V˙O2max

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534 Section 4 Enhancement of Energy Transfer Capacity

➤ Discuss the medical use of erythropoietin and ➤ Outline the classic carbohydrate-loading proce- potential dangers for healthy athletes dure and modified-loading procedure to augment glycogen storage ➤ Define general warm-up and specific warm-up and the potential benefits of each ➤ Describe the theoretical role for an ergogenic effect of creatine supplements, and indicate phys- ➤ Describe possible cardiovascular benefits of ical activities that benefit from supplementation moderate warm-up prior to extreme physical effort ➤ Summarize the research and rationale for consuming medium-chain triacylglycerols to ➤ Provide a rationale for breathing hyperoxic gas enhance endurance performance mixtures to enhance exercise performance; quantify its potential to increase tissue oxygen ➤ Discuss the effects of pyruvate supplementation availability on endurance and body fat loss

Considerable literature exists about ergogenic aids and ath- runners in the 1908 Olympics to drink alcohol (brandy) to im- letic performance—ergogenic referring to the application of a prove performance, and in the early 1970s athletes were fed nutritional, physical, mechanical, psychologic, or pharmaco- high-carbohydrate meals by “personal nutritionists” before logic procedure or aid to improve physical work capacity or competition to decrease muscle fatigue. Use of ergogenic aids, athletic performance. This literature includes studies of poten- including illegal drugs, to improve exercise performance in tial performance benefits of alcohol, amphetamines, ephedrine, almost all sports has been making headlines since the 1950s, hormones, carbohydrates, amino acids, fatty acids, additional and unfortunately illegal doping has continued into the 2008 red blood cells, caffeine, carnitine, creatine, phosphates, oxy- Tour de France (Kazakhstan’s Dmitri Fofonov, Italy’s gen-rich breathing mixtures, massage, wheat-germ oil, vita- Riccardo Ricco, and Spain’s duo Manuel Beltran and Moises mins, minerals, ionized air, music, hypnosis, and even Duenas) and six athletes in the 2008 Beijing Olympic Games marijuana and cocaine! Athletes routinely use only a few of (as of June 10, 2009). these aids, and only a few evoke real controversy. Specific con- Improvements in doping control for the 2004 Athens cern focuses on the use of anabolic steroids, human growth hor- Olympics have apparently had a major impact on sports per- mone, dehydroepiandrosterone (DHEA), and other exogenous formance. FIGURE 23.1 shows the lack of improvement in new hormones and prohormones, nutritional components, ampheta- world records, mainly in track and field, as evidence that the mines, and “blood doping.” Warm-up and breathing hyperoxic drug-tainted past has temporarily been put on hold. Twenty- gas are common procedures, so we include these in our discus- three athletes were barred from the 2004 games and only one sion of the effectiveness and practicality of ergogenic aids for world record was tied (12.92 s in the 110-m men’s hurdles). exercise training and performance. Note particularly the decline in men’s and women’s perform- We discuss nutritional requirements for macro- and micro- ances in the shot put, discus, javelin, and long jump. nutrients for active individuals in the specific chapters dealing Unfortunately, highly celebrated and idolized but now dis- with these nutrients. The increasing use of herbs of undocu- graced Olympians were required by the International Olympic mented quality by fitness enthusiasts and athletes raises concern Committee (IOC) to return their medals for illegal doping dur- about efficacy and possible toxicity. “In a Practical Sense” on ing the 2000 Sydney Olympic Games. Track star Marion Jones, page 535 summarizes ingredients, purported benefits, and possi- who won five medals (gold in the 100-m, 200-m, and 1600-m ble side effects of commonly used herbal compounds. relay and bronze in the long jump and 40-m relay), pleaded The indiscriminate use of ergogenic substances increases guilty to two counts of lying to investigators about her doping the likelihood of adverse side effects that range from benign abuse and was sentenced to federal prison for 6 months, includ- physical discomfort to life-threatening episodes. Many of ing two years’ probation and community service. these compounds fail to conform to labeling requirements to correctly identify the strength of the product’s ingredients and contaminents.111,140 Urine Testing: The Method of Choice Testing of urine samples provides the primary method for drug detection. Chemicals are added to AN INCREASING CHALLENGE the urine sample, which is then heated and vaporized TO FAIR COMPETITION in testing. The vapor passes through an absorbent column and an electric or magnetic field (gas Examples of ergogenic use by athletes date to antiquity. chromatography-mass spectrometry). The pattern Physicians encouraged Roman and Greek athletes to eat raw made by the molecules deflected by the field is com- meat before competing to enhance their “animal competitive- pared with patterns made by known chemicals. ness.” In more modern times, trainers advised marathon 97818_ch23.qxd 8/4/09 4:46 PM Page 535

CHAPTER 23 Special Aids to Exercise Training and Performances 535

IN A PRACTICAL SENSE Commonly Used Herbal Compounds for Exercise and Training: User Beware

Aside from the influence of genetics and proper training, nutrition Intake of a broad range of herbal compounds as supplements for often exerts an important influence on athletic performance. In seek- ergogenic purposes has expanded considerably during the last ing the competitive edge, exercise enthusiasts and athletes fall prey to decade. Aside from the lack of documentation concerning the effi- fad diets and unnecessary supplements whose potency, quality, and cacy of these chemicals, many carry the potential for health risk. effectiveness lack scientific validation. Athletes often eat a suboptimal The prudent coach and exercise specialist should know the com- diet, particularly when attempting to reduce body weight while train- mon herbs used by athletes and their purported effects, contraindi- ing strenuously. This leads to the use of a diverse array of “nutritional” cations, and possible adverse side effects. The table lists the more supplements, including herbal compounds (used by 23% of U.S. popular herbs with uses, active ingredients, common dosage, and adults), to hopefully overcome nutritional inadequacies and insure precautionary information. optimal performance and training responsiveness.

Herbs Frequently Used to Improve Health, Reduces Stress, Elevate Emotional and Cognitive Responses, Enhance Muscular Development and Exercise Performance, and Speed Recovery Side Effects/ Purported Interactions/ Herb Other Name Use/Benefit Active Ingredients Dosage Comments Astragulus Huang qi Supports immune Flavonoids, polssaccharides, 9Ð15 g и dϪ1 None system; benefits triterpene glycosides, cardiovascular system; amino acids, and trace increases energy minerals level; promotes tissue repair Bilberry Vaccinium Diabetes; macular Anthocyanosides 240Ð600 mg и dϪ1 None myrtillus degeneration; (bioflavonoid) as herbal extract retinopathy or 20Ð60 g и dϪ1 fruit Bee pollen Buckwheat Allergies; asthma; Protein, carbohydrates, 500Ð1000 mg и dϪ1 Allergic reactions; pollen; cholesterol and minerals, and essential avoid with puhuang triacylglycerol fatty acids hypoglycemic lowering agents Chamomile Camomile, Stress reduction; ␣-Bisabol; bioflavonoids Taken as tea Avoid if allergic roman supports immune 3 to 4 times to plants camomile function; assists per day sleep; promotes tissue repair Echinacea Echinacea Common cold/sore Alkylamides, polyacetylenes; At onset of cold Avoid if allergic to purpurea; throat; immune increases interferon or flu; sunflower plant echinacea function; infection; production 3Ð4 mL и 2hϪ1 family angustifolia influenza or 300 mg powder и dϪ10 Ephedra Ephedra sinica; Asthma; cough; weight Alkaloids ephedrine and 1.5Ð6 g и dϪ1 in tea Banned substance; Ephedra loss; increases energy pseudo-ephedrine form; 12.5Ð amphetamine-like equisetina level 25 mg и 4 hϪ1 as side effects; avoid over-the-counter with hypertension drug or pregnancy Garlic Allium sativum High blood pressure; high Sulfer compound allicin 600Ð900 mg и dϪ1 Avoid with stomach triacylglycerols; problems; intermittent claudication heartburn, gastritis, or ulcers

Continued on page 536 97818_ch23.qxd 8/4/09 4:46 PM Page 536

536 Section 4 Enhancement of Energy Transfer Capacity

Ginseng, Pannax Mental alertness; memory; Eleutherosides 200Ð600 mg и dϪ1 Avoid with Asian physical endurance; hypertension, type 2 diabetes; heart disease; hyperlipidemia; pregnancy and congestive heart failure lactation; nervousness; fever or sleep disorders Ginseng, Eleuthero root Physical endurance; fatigue Eleutherosides 200Ð600 mg и dϪ1 Avoid with hyperten- Siberian prevention; immune sion, heart disease; function; motion sickness pregnancy; and lactation; nervousness; fever or sleep disorders Ginkgo Maidenhair Age-related cognitive Gingko flavone glycosides 120Ð240 mg и dϪ1 Mild headaches biloba tree decline; Alzheimer’s (bioflavonoid), terpene lasting 1 or 2 days; disease; intermittent (lactones) mild upset stomach claudication; depression; atheroscleroisis; impotence (of vascular origin) Guarana Paullinia Fatigue prevention; Guaranine (identical to 200Ð800 mg и dϪ1 Avoid with pregnancy, cupana weight loss caffeine) glucoma, heart disease, high blood pressure, history of stroke Kava Kava Piper Anxiety; restlessness; stress, Kava-lactones 200Ð250 mg и dϪ1 Avoid with pregnancy methysticum muscle relaxing or if lactating; can cause drowsiness Milk thistle Silybum Alcohol-related liver Bioflavonoid complex- 200Ð400 mg и dϪ1 None marianum disease; hepatitis; liver silymarin support Glucosamine Osteoarthritis; joint 1500 mg и dϪ1 Avoid with diabetes sulfatea inflammation; joint stiffness Grape seed Circulatory disorders; 75Ð300 mg и dϪ1 None extract varicose veins; atherosclerosis Saw Serenoa Benign prostatic hyper- Liposterolic extract of saw 200Ð300 mg и dϪ1 None palmetto repens, sabal plasia; urination problems palmetto provides fatty serrulata in males acids, sterols, and esters St. John’s Hypericum Depression; anxiety or Hypericin, flavonoids 900 mg и dϪ1 Heightens sun wort perforatum nervous unrest; mood sensitivity; disturbance of interferes with menopause iron absorption Witch hazel Hamamelis Eczema; hemorrhoids; Tannins and volatile oils As ointment Not for internal use; virginiana varicose veins or cream 3Ð causes stomach 4 times и dϪ1 irritation Yohimbe Pausinystalia Impotence; depression Yohimbine (alkaloid) 15Ð30 mg и dϪ1 Use only under ohimbe medical supervision Valerian Heliotrope; Stress reduction; improves Essential oils 300Ð500 mg before None setwall; sleep; benefits sleep vandal root cardiovascular system

aNot truly listed as an herb; usually listed as a supplement. From Fetrow C, Avila JR. Professionals handbook of complementary & alternative medicines. Springhouse, PA: Springhouse Corporation, 1999; and Schuyler W, et al. The natural pharmacy. 2nd ed. New York: Three Rivers Press. Imprint of Crown Publishing Group, 1999. 97818_ch23.qxd 8/4/09 4:46 PM Page 537

CHAPTER 23 Special Aids to Exercise Training and Performances 537

Percentage Difference 2004 Winning from World Record Men World Record (Year) Time/Distance –15 –10 –5 0 100M 9.78 (2002) 9.85 – 0.7

200M 19.32 (1996) 19.79 – 2.4 400M 43.18 (1999) 44.00 – 1.9

800M 1:41.11 (1997) 1:44.45 – 3.3

1500M 3:26.00 (1998) 3:34.20 – 4.0 5000M 12:37.35 (2004) 13.14.39 – 4.9 10,000M 26:20.31 (2004) 27:05.10 – 2.8 Steeplechase 7:55.28 (2001) 8:05.80 – 2.2

110M Hurdles 12.91 (1993) 12.91 Tied World Record 400M Hurdles 46.78 (1992) 47.63 – 1.8

Shot-put 75.10 1/4 (1990) 69-5 1/4 – 8.5

Discus 243 (1986) 229-3 1/2 – 5.7 Hammer 284-7 (1986) 272-11 1/4 – 4.1

Javelin 323-1 (1996) 283-9 1/2 – 12.2

Long Jump 29-4 1/2 (1991) 28-2 1/4 – 4.0

Triple Jump 60- 1/4 (1995) 58-4 1/2 – 2.7 High Jump 8- 1/2 (1993) 7-8 3/4 – 3.7

Pole Vault 20- 1 3/4 (1994) 19-6 1/4 – 3.1

Decathlon 9026 (2001) 8893 – 1.5

Percentage Difference 2004 Winning from World Record Women World Record (Year) Time/Distance –15 –10 –5 0

100M 10.49 (1988) 10.93 – 4.2 200M 21.34 (1988) 22.05 – 3.2

400M 47.60 (1985) 49.41 – 3.8

800M 1:53.28 (1983) 1:56.38 – 2.7 – 3.2 1500M 3:50.46 (1993) 3:57.90

5000M 14:24.68 (2004) 14.45.65 – 2.4

10,000M 29:31.78 (2004) 30:24.36 – 3.0

110M Hurdles 12.21 (2001) 12.37 – 1.3

400M Hurdles 52.34 (1993) 52.82 – 0.9

Shot-put 74-3 (1987) 64- 3 1/4 – 13.4

Discus 252 (1988) 219- 10 1/2 – 12.7

Hammer 249-7 (1999) 246-1 1/2 – 1.4 Figure 23.1 • Track and field 234-8 1/4 world records compared with Javelin 234-8 1/2 (2001) – 0.01 2004 Athens Olympic Long Jump 24-8 (1988) 23-2 1/2 – 6.0 performances. Negative values Triple Jump 50-10 1/4 (1995) 50-2 1/2 – 1.3 (red) reflect poorer performances in Athens for men (top) and High Jump 6- 10 1/4 (1987) 6-9 – 1.4

women (bottom). Note the gold- Pole Vault 16- 3/4 (2004) 16-11/4 + 0.20 colored area for the events that Heptathlon 7291 (1988) 6952 – 4.7 emphasize muscular strength and power. 97818_ch23.qxd 8/4/09 4:46 PM Page 538

538 Section 4 Enhancement of Energy Transfer Capacity A NEED TO CRITICALLY EVALUATE fail to demonstrate whether the same effects occur THE SCIENTIFIC EVIDENCE if subjects received the supplement with their baseline nutrient intake at recommended levels. It Companies expend considerable money and effort to show a should occasion little surprise, for example, that beneficial effect of an “aid.” Often, however, a placebo ef- supplemental iron enhances aerobic fitness in a fect, not the “aid,” improves performance because of psycho- group with iron-deficiency anemia. One cannot logical factors—the individual performs at a higher level infer, however, that iron supplements provide such because of the suggestive power of believing that a substance benefits to all individuals. or procedure should work. Those in the exercise sciences ¥ Health status: Nutritional, hormonal, and phar- must evaluate the scientific merit of articles and advertise- macologic interventions profoundly affect the ments about products and procedures. To separate marketing diseased and infirmed yet offer no benefit to “hype” from scientific fact, we pose five areas for questioning those in good health. Research findings from dis- the validity of research claims concerning the efficacy of eased groups should not be generalized to healthy chemical, pharmacologic, and nutritional ergogenic aids: populations. I. Justification III. Research sample, subjects, and design ¥ Scientific rationale: Does the study represent a ¥ Random assignment or self-selection: Apply re- “fishing expedition” or is there a sound rationale search findings only to groups similar to the sam- that the specific treatment should produce an effect? ple studied. If subject volunteers “self-select” into For example, a theoretical basis exists to believe an experimental group, does the experimental that ingesting creatine elevates intramuscular crea- treatment produce the results, or did a change tine and phosphocreatine to possibly improve short- occur from the individual’s motivation to take part term power output capacity. In contrast, no rationale in the study? For example, desire to enter a weight exists to hypothesize that hyperhydration, breathing loss study may elicit behaviors that produce hyperoxic gas, or ingesting medium-chain triacyl- weight loss independent of the experimental treat- glycerols should enhance 100-m dash performance. ment per se. Great difficulty exists in assigning II. Subjects truly random samples of subjects into an experi- ¥ Animals or humans: Many diverse mammals ex- mental group and a control group. When subjects hibit similar physiologic and metabolic dynamics, volunteer to take part in an experiment, they must yet significant species differences exist, which be randomly assigned to a control or experimental often limit generalizations to humans. For exam- condition, a process termed randomization. ple, the models for disease processes, nutrient re- When all subjects receive the experimental sup- quirements, hormone dynamics, and growth and plement and the placebo treatment (see below), development often differ markedly between hu- supplement administration is counterbalanced, mans and different animal groups. and half the subjects receive the supplement first, ¥ Sex: Sex-specific responses to the interactions be- while the other half takes the placebo first. tween exercise, training, and nutrient requirements ¥ Double-blind, placebo-controlled: The ideal exper- and supplementation limit generalizability of find- iment to evaluate performance-enhancing effects ings to the sex studied. of an exogenous supplement requires that experi- ¥ Age: Age often interacts to influence the outcome mental and control subjects remain unaware, or of an experimental treatment. Effective interven- “blinded” to, the substance administered. To tions for the elderly may not apply to growing chil- achieve this goal, subjects should receive a similar dren or young and middle-aged adults. quantity and/or form of the proposed aid. In con- ¥ Training status: Fitness status and training level trast, control group subjects receive an inert com- can influence the effectiveness (or ineffectiveness) pound or placebo. The placebo treatment evaluates of a particular diet or supplement intervention. the possibility of subjects performing well or Treatments that benefit the untrained (e.g., chemi- responding better simply because they receive a cals or procedures that enhance neurologic disinhi- substance they believe should benefit them (psy- bition) often have little effect on elite athletes who chological or placebo effect). To further reduce practice and compete routinely at maximal arousal experimental bias from influencing the outcome, levels. those administering the treatment and recording the ¥ Baseline level of nutrition: The research should es- response must not know which subjects receive the tablish the subjects’ nutritional status prior to ex- treatment or placebo. In such a double-blinded experimental treatment. Clearly, a nutrient periment, both investigator and subjects remain un- supplement administered to a malnourished group aware of the treatment condition. FIGURE 23.2 typically improves exercise performance and train- illustrates the design of a double-blind, placebo- ing responsiveness. Such nutritional interventions controlled study with an accompanying crossover 97818_ch23.qxd 8/4/09 4:46 PM Page 539

CHAPTER 23 Special Aids to Exercise Training and Performances 539

Select subjects

PreTest (all subjects)

Placebo Treatment condition Random assignment condition

Posttest Compare results Posttest

Treatment Placebo condition Crossover condition

Posttest Compare results Posttest

Figure 23.2 • Example of a randomized, double-blind, placebo-controlled, crossover study. Following appropriate subject selection, participants are pretested and then randomly assigned to either the experimental (treatment) or control (placebo) group. Following treatment a posttest is administered. Participants then cross over into the opposite group for the same time period as in the first condition. A second posttest follows. Comparisons of the posttests determine the extent of a “treatment effect.”

where treatment and placebo conditions are implications and generalizations of research find- reversed. ings must remain within the context of the mea- ¥ Control of extraneous factors: Under ideal condi- surements made, the subjects studied, and the tions, experiences should be similar for both exper- magnitude of the response. For example, increases imental and control groups, except for the in anabolic hormone levels in response to a dietary treatment variable. Random assignment of subjects supplement reflect just that; they do not necessar- to control or experimental groups goes a long way ily indicate an augmented training responsiveness to equalize control factors that could influence the or an improved level of muscular function. study’s outcome. Similarly, improvement in brief anaerobic power ¥ Appropriateness of measurements: Reproducible, output capacity with creatine supplementation objective, and valid measurement tools must evalu- does not justify the conclusion that exogenous create research outcomes. For example, a step test to atine improves overall “physical fitness.” predict aerobic capacity, or infrared interactance to ¥ Appropriate statistical analysis: Appropriate inferen- evaluate components of body composition, repre- tial statistical analysis must be applied to quantify sents an imprecise tool to answer meaningful ques- the potential that chance caused the research out- tions about the efficacy of a proposed ergogenic aid. come. Other statistics must objectify averages, vari- IV. Conclusions ability, and degree of association between variables. ¥ Findings should dictate conclusions: The conclu- ¥ Statistical versus practical significance: The find- sions of a research study must logically follow ing of statistical significance of a particular experi- from the research findings. Frequently, investiga- mental treatment only means a high probability tors who study ergogenic aids extrapolate conclu- exists that the result did not occur by chance. One sions beyond the scope of their data. The must also evaluate the magnitude of an effect for 97818_ch23.qxd 8/4/09 4:46 PM Page 540

540 Section 4 Enhancement of Energy Transfer Capacity its real impact on physiology and/or performance. randomized, double-blind, placebo-controlled studies published A reduced heart rate of 3 beats per minute during in peer-reviewed journals. But even the results of the best submaximal exercise may reach statistical signifi- designed research may not be enough. Reproducible results be- cance, yet have little practical effect on aerobic fit- come an important part of the evaluation process such that ness or cardiovascular function. strongest evidence emerges from the cumulative body of scientific literature and not simply the results of one study. Clearly, it V. Dissemination of findings is highly desirable that research evidence be strong before mak- ¥ Published in peer-reviewed journal: High-quality ing recommendations about a given ergogenic aid. This, how- research withstands the rigors of critical review ever, is not always possible, and recommendations are made and evaluation by colleagues with expertise in the supported only by fair or limited evidence, often anecdotal in specific area of investigation. Peer review pro- nature. We maintain that until strong evidence supports use of a vides a measure of quality control over scholarship purported ergogenic substance, athletes and those involved in and interpretation of research findings. Publications training, coaching, and advising these individuals should under- in popular magazines or quasi-professional journals stand the relative strength of available research in this area, as do not undergo the same rigor of evaluation as peer presented in Table 23.1. review. In fact, self-appointed “experts” in sports nutrition and physical fitness pay eager publishers for magazine space to promote their particular ON THE HORIZON viewpoint. In some cases, the expert owns the The day may be near when individuals born lacking certain magazine! “lucky” genes that augment growth and development and ¥ Findings reproduced by other investigators: exercise performance will simply add them, doping unde- Findings from one study do not necessarily estab- tectably with DNA, not drugs. In these instances, the use of lish scientific fact. Conclusions become stronger “gene doping” misappropriates the medical applications of and more generalizable when support emerges gene therapy that treats atherosclerosis, cystic fibrosis, and from the laboratories of other independent investi- other potentially debilitating and deadly diseases. Gene doping gators. Consensus reduces the influence of chance, offers the promise to increase the size, speed, and strength of flaws in experimental design, and investigator bias. healthy humans. Genes that cause muscles to enlarge would be ideal for sprinters, weightlifters, and other power athletes. Levels of Evidence Endurance athletes would benefit from genes that boost red blood cell production (e.g., gene for erythropoietin) or stimu- The National Heart, Lung and Blood Institute (NHLBI; part of late blood vessel development (e.g., gene for vascular endothe- the National Institute of Health [NIH]) issued guidelines to lial growth factor). The world of sports doping has changed consider when judging the strength of research evidence. The dramatically in the past 15 years, and it seems that thrust will evidence guidelines presented in TABLE 23.1 indicate that continue, but this time the athletes will have access to a new the strongest and most conclusive evidence comes from arsenal of “magic bullet” genetically engineered drugs.

TABLE 23.1 • Levels of Evidence on Which to Judge Research Findings

Evidence Category Source of Evidence Definition and Comment

I Randomized controlled trials Evidence derives from endpoints of well-designed RCTs (or trials that depart (RCTs) involving a rich body only minimally from randomization) that provide a consistent pattern of of data data of findings in the population for which the recommendation is made. Requires substantial number of participants. Very high confidence in findings. II RCTs involving a limited Evidence from endpoint of intervention studies that include only a limited body of data number of RCTs, post hoc or subgroup analysis of RCTs, or metaanalysis of RCTs. In general, this line of evidence is less convincing than level I because of some inconsistency in the results between studies. III Nonrandomized trials and Evidence derived from outcomes of uncontrolled or nonrandomized observational studies trials or from observational studies. IV Panel consensus judgment Expert judgment derived from experimental research described in the literature and/or derived from the consensus of panel members, based on clinical experience or knowledge that does not meet the above listed criteria on other levels. This category is used only in cases where the provision of some guidance was deemed valuable, but an adequately compelling clinical literature addressing the subject of the recommendation was deemed insufficient to justify placement in one of the other categories (I or III). 97818_ch23.qxd 8/4/09 4:47 PM Page 541

CHAPTER 23 Special Aids to Exercise Training and Performances 541 Anabolic Steroids Mechanism for How Purported Ergogenic Aids Might Work Anabolic steroids gained prominence in the early 1950s for medical purposes, to treat patients deficient in natural andro- ¥ Act as a central or peripheral nervous system gens or with muscle-wasting diseases. Other legitimate steroid stimulant (e.g., caffeine, choline, amphetamines, uses include treatment of osteoporosis and severe breast alcohol) cancer in women, and countering the excessive decline in lean ¥ Increase storage and/or availability of a limiting body mass and increase in body fat often observed in elderly substrate (e.g., carbohydrate, creatine, carnitine, men, HIV patients, and individuals who undergo kidney chromium) dialysis. ¥ Act as a supplemental fuel source (e.g., glucose, medium-chain triacylglycerols) ¥ Reduce or neutralize performance-inhibiting INTEGRATIVE QUESTION metabolic byproducts (e.g., sodium bicarbonate A student maintains that a chemical compound or sodium citrate, pangamic acid, phosphate) added to his diet produced profound improve- ¥ Facilitate recovery (e.g., high-glycemic carbo- ments in weightlifting performance. Your review hydrates, water) of the research literature indicates no ergogenic ¥ Enhance resistance-training responsiveness benefits for this compound. How would you (anabolic steroids, human growth hormone, reconcile the discrepancy? carbohydrate/protein supplements immediate postexercise)

Current estimates suggest that up to 4 million athletes (90% of male and 80% of female professional bodybuilders) currently use androgens, often combined with stimulants, hor- PHARMACOLOGIC AGENTS mones, and diuretics. Even in the sport of professional base- Athletes go to great lengths to promote all aspects of their ball, interviews of strength trainers and current players health: they train hard; eat well-balanced meals; consume the estimate that up to 30% of the players use anabolic steroids in latest sports drink with megadoses of vitamins, minerals, and their quest to enhance hitting and pitching performance. amino acids; and seek and receive medical advice for various injuries (no matter how minor). Yet ironically, they will ingest Structure and Action synthetic agents, many of which precipitate adverse effects ranging from nausea, hair loss, itching, and nervous irritability, Anabolic steroids function in a manner similar to testos- to severe consequences such as sterility, liver disease, drug ad- terone, the chief male hormone. By binding with receptor diction, and even death caused by liver and blood cancer. sites on muscle and other tissues, testosterone contributes to The World Anti-Doping Agency (WADA; www. male secondary sex characteristics. This includes gender dif- wadaama.org/en/prohibitedlist.ch2) currently bans the fol- ferences in muscle mass and strength that develop at puberty lowing nine categories of substances: onset. Testosterone production takes place mainly in the testes (95%), with the adrenal glands producing the remainder. 1. Anabolic androgenic steroids Synthetically manipulating the steroid’s chemical structure to 2. Hormones and related substances increase muscle growth (from anabolic tissue building and 3. Beta 2 agonists nitrogen retention) reduces the hormone’s androgenic or mas- 4. Hormone antagonists and modulators culinizing effects. A masculinizing effect of synthetically de- 5. Diuretics and other masking agents rived steroids still exists, particularly for females. 6. Stimulants Athletes typically combine multiple steroid preparations 7. Narcotics in oral and injectable form, a practice called stacking, because 8. Cannabinoids they believe that the various androgens differ in physiologic 9. Glucocorticosteroids action. They also progressively increase drug dosage—a prac- The Prohibited List was first published in 1963 (www. tice called pyramiding—usually in 6- to 12-week cycles. The olympic.org/). Since 2004, as mandated by the World Anti- drug quantity far exceeds the recommended medical dose, Doping Code, WADA prepares and publishes the List. The List often by 40-fold. The athlete then progressively reduces drug and Code represent an International Standard that identifies dosage in the months before competition to lower the chance substances and methods prohibited in competition, out of of detection during drug testing. The difference between competition, and in particular sports. WADA is composed of a dosages used in research studies and those used by athletes Foundation Board, an Executive Committee, and several other contributes to the credibility gap between scientific findings committees. The 38-member Foundation Board acts as WADA’s (often, little effect of steroids) and what most in the athletic supreme decision-making body and consists of representatives community “know” to be true through trial-and-error self- from the Olympic Movement and various governments. experimentation. 97818_ch23.qxd 8/4/09 4:47 PM Page 542

542 Section 4 Enhancement of Energy Transfer Capacity Designer Drug Unmasked. Researchers in the specific drugs and dosages, treatment duration, accompany- Department of Molecular and Medical Pharmacology at ing nutritional supplementation, training intensity, evaluation UCLA’s Olympic Analytical Laboratory (www.pathnet. techniques, previous experience of subjects, and individual medsch.ucla.edu/OlympicLab/index.html) unmasked an illegal differences in responsiveness to a drug’s effectiveness. The “designer” compound that mimics the chemical structure of the relatively small residual androgenic effect of the steroid facil- banned steroids gestrinome and trenbolone. Discovery of this itates central nervous system activation to make the athlete new stand-alone steroid chemical entity, not a “pro-steroid” or more aggressive (so-called roid rage), competitive, and “precursor steroid” like many performance-boosting substances fatigue resistant. Such facilitatory effects allow the person to on the market, introduced a drug with no prior record of manu- train harder for a longer time or to believe that augmented facture or existence. An anonymous tipster provided a syringe training effects have actually occurred. Abnormal mood alter- sample of the steroid identified as tetrahydrogestrinone, or ations and psychiatric dysfunction sometimes accompany an- THG. The researchers developed a new test to detect THG, ap- drogen use.53,96 parently taken not by injection but in droplets under the tongue. Research with animals suggests that anabolic steroid They then reanalyzed 350 urine samples from participants at the treatment combined with exercise and adequate protein intake U.S. track and field championships in June 2003 and 100 sam- stimulates protein synthesis and increases muscle protein con- ples from random out-of-competition tests. A remarkably high tent (myosin, myofibrillar, sarcoplasmic factors).222 In con- half-dozen athletes tested positive. On October 17, 2003, the trast, other research revealed that steroid treatment did not National Football League began testing players for THG to benefit leg muscle weight of rats subjected to functional over- avoid the scandal that has embarrassed track and field. load by surgical removal of the synergistic muscle.170 Treatment with anabolic steroids did not complement functional overload to stimulate additional muscular development. A Drug with a Considerable Following The situation with humans is difficult to interpret. Some One often pictures steroid abusers as extremely muscular studies show that steroid use by men who train augments bodybuilders, but abuse also occurs among competitive ath- body mass gains and reduces body fat, while other studies letes in road cycling, tennis, track and field, American colle- show no effect on strength and power or body composition, giate and professional football, canoeists, auto racing, even with sufficient energy and protein intake to support an swimming, and other highly competitive sport activities. anabolic effect.91 When steroid use produces body weight Surveys of United States Powerlifting Team members indicate gains, the compositional nature of the gains (water, muscle, that up to two-thirds used androgenicÐanabolic steroids.65 fat) remains unclear. Patients receiving dialysis and those in- Many competitive and recreational athletes obtain steroids on fected with the HIV virus commonly experience malnutrition, the black market. Thus, misinformed individuals may take a decrease in muscle mass, and chronic fatigue. Dialysis massive and prolonged dosages without medical monitoring patients given 6 months of supplementation with the anabolic and suffer harmful alterations in physiologic function. steroid nandrolone decanoate increased lean body mass and Steroid abuse among adolescents and its accompanying level of daily function.138 Similarly, in men with HIV, a mod- risks, including extreme virilization and premature cessation erately supraphysiologic androgen regimen that included the of bone growth, remains particularly worrisome. Boys and anabolic steroid oxandrolone increased lean tissue accrual girls as young as 11 years of age use anabolic-androgenic and strength gains from resistance training substantially more steroids.87 Teenagers cite improved athletic performance as than physiologic testosterone replacement alone.251 the most common reason for taking steroids, although 25% acknowledge enhanced appearance as a main reason. In this Dosage Is an Important Factor regard, a body image disturbance may contribute to anabolic steroid abuse among teenagers and adults.192,292 The National In many instances, dosage variations contribute to confu- Institutes of Drug Abuse, an arm of the National Institutes of sion and create a credibility gap between scientist and steroid Health, claims that steroid use among high school sopho- user regarding effectiveness. One study focused on 43 healthy mores more than doubled nationwide between 1992 and men with some resistance-training experience. Experimental 2000. A Blue Cross/Blue Shield national survey noted a 25% controls accounted for diet (energy and protein intake) and ex- increase in steroid and similar drug use from 1999 to 2000 ercise (standard weightlifting, 3 times weekly) with steroid among boys ages 12 to 17. dosage (600 mg of testosterone enanthate injected weekly or placebo) exceeding values in previous studies with humans. FIGURE 23.3 illustrates changes from baseline values for fat-free Effectiveness Questioned body mass (FFM; hydrostatic weighing), triceps and quadri- For five decades, researchers and athletes have debated ceps cross-sectional muscle areas (magnetic resonance imag- the true effect of anabolic steroids on human body composi- ing), and muscle strength (1-RM) after 10 weeks of treatment. tion and exercise performance. Much of the confusion about The men who received the hormone while continuing to train the ergogenic effectiveness of anabolic steroids stems from gained about 0.5 kg of lean tissue weekly with no increase in variations in experimental design, lack of control groups, body fat. Even the group receiving the drug without training 97818_ch23.qxd 8/4/09 4:47 PM Page 543

CHAPTER 23 Special Aids to Exercise Training and Performances 543 for anemia, renal insufficiency, impotence, or pituitary gland dysfunction. Prolonged high dosages of steroids (often at lev-

) 6 els 10 to 200 times therapeutic recommendations) can lead to 4 f ree long-lasting impairment of normal testosterone endocrine 2 function. In male power athletes, for example, 26 weeks of Fat-

mass (k g 0 steroid administration reduced serum testosterone to less than one-half the level when the study began, with the effect last- 91 ) 600 ing throughout a 12- to 16-week follow-up. Infertility, re- 2 400 duced sperm concentrations (azoospermia), and decreased testicular volume pose additional problems for the steroid 200 Triceps Triceps user.99 Gonadal function usually returns to normal within sev-

area (mm 0 eral months after cessation of steroid use. Other hormonal alterations during steroid use by males include a sevenfold g e ) 1200 2 increase in estradiol concentration, the major female hor- an 800 mone. The higher estradiol level represented the average 400 value for normal females; this possibly explains the gyneco- Quadriceps

area (mm 0 mastia (usually irreversible, excessive development of the Mean c h male mammary glands, sometimes secreting milk) often re- 20 ported when taking anabolic steroids.

(k g ) Steroid use with exercise training may damage connective -press

h 10 tissue to decrease tendon tensile strength and elastic compliance.162 Steroids also cause the following:3,72,92,105,118,142,254

Benc 0 stren g t h 1. Chronic stimulation of the prostate gland (with pos- 40 sible size increase) (k g ) 30 2. Injury and functional alterations in cardiovascular 20

S quat 10 function and myocardial cell cultures 0 3. Decreased diastolic relaxation and exacerbation of stren g t h No exercise Exercise normal cardiac hypertrophy with resistance training; potential negative effects on thyroid gland function and hormone action Placebo Testosterone 4. Increased blood platelet aggregation, which could Figure 23.3 • Changes from baseline in average fat-free compromise cardiovascular system health and func- body mass, triceps and quadriceps cross-sectional areas, and tion and possibly increase risk of stroke and myocar- muscle strength in bench press and squatting exercises over dial infarction 10 weeks of testosterone treatment. (From Bhasin S, et al. The effects of supraphysiological doses of testosterone on Dramatic life shortening resulted for adult mice ex- muscle size and strength in normal men. N Engl J Med posed for 6 months to the type and relative levels of steroids 1996;335:1.) used by athletes. One year after termination of steroid exposure, 52% of mice given a high steroid dose died compared with 35% given a low steroid dosage and only 12% of the increased muscle mass and strength compared with men receiv- control animals given no exogenous hormones (FIG. 23.4). ing the placebo. Notably, their increases averaged less than men Autopsy of steroid-treated mice revealed a broad array of who trained while taking testosterone. The researchers empha- pathologic effects that did not appear until long after steroid sized that that they did not design the study to justify or endorse use ceased—liver and kidney tumors, lymphosarcomas, and steroid use for athletic purposes because of the health risks (see heart damage, frequently in combination. A 6-month expo- next section). These data did, however, indicate a potential for sure represents about one-fifth of a male mouse’s life ex- medically supervised anabolic steroid treatment to restore and pectancy, a relative duration considerably longer than enhance muscle mass in individuals suffering from tissue- exposure of most humans to steroid use. Liver damage rep- wasting diseases. resents a typical effect in athletes who take steroids. If such findings prove applicable to humans, several decades may elapse before the true negative effects of anabolic steroid Risks Do Exist use emerge. Whether anabolic steroid use by athletes carries health risks remains controversial because research on risk generally has Steroid Use and Life-Threatening Disease. TABLE 23.2 involved medical observations of hospitalized patients treated lists adverse effects and medical risks of anabolic steroid use. 97818_ch23.qxd 8/4/09 4:47 PM Page 544

544 Section 4 Enhancement of Energy Transfer Capacity called peliosis hepatitis, is one of the serious effects of androgens on the liver. In the extreme case, the liver eventually 100 fails and the patient dies. We present these data not as a scare tactic but to emphasize the potentially serious adverse effects, even when a physician prescribes the drug in the recom- 75 mended dosage. Patients often take steroids for a longer dura- Steroid tion than do athletes, yet some athletes take steroids on and Exposure off for years at dosages exceeding typical therapeutic levels of 50Ð200 mg и dϪ1 versus the usual therapeutic dosage of 50 Ϫ1 g e survivin g 5Ð20 mg и d .

Steroid and Plasma Lipoproteins. Anabolic steroid 25 use (particularly the orally active 17-alkylated androgens) by Percenta healthy men and women reduces high-density lipoprotein cholesterol (HDL-C) levels, elevates both low-density 0 lipoprotein cholesterol (LDL-C) and total cholesterol levels, 0462 8 1012141618202224 and reduces the HDL-C:LDL-C ratio.56 Weightlifters who Age (months) take anabolic steroids averaged an HDL-C level of 26 mg и dLϪ1 compared with 50 mg и dLϪ1 for weightlifters not taking 141 Control Low dose High dose this drug! Reducing HDL-C to this level increases a steroid user’s risk of coronary artery disease. The dramatically low Figure 23.4 • Life-shortening effects of exogenous anabolic HDL-C levels among weightlifters remain low, even after steroid use in mice. (Modified from Bronson FH, Matherne they abstain for at least 8 weeks between consecutive steroid CM. Exposure to anabolic–androgenic steroids shortens life cycles.228 The long-term effects of steroid use on cardiovas- span of male mice. Med Sci Sports Exerc 1997;29:615.) cular morbidity and mortality remain unknown.

American College of Sports Medicine Position Concern centers on possible links between androgen abuse Statement on Anabolic Steroids. As part of their long-range and abnormal liver function. Because the liver almost exclu- educational program, the American College of Sports Medicine sively metabolizes androgens, it becomes susceptible to dam- (ACSM; www.acsm.org/) has taken a stand on the use of age from long-term steroid use and toxic excess. The anabolic-androgenic steroids, which appears in the following development of localized blood-filled lesions, a condition FYI6:

TABLE 23.2 • Side Effects and Medical Risks of Anabolic Steroid Use

Males Females

Increase Decrease Increase Decrease

Testicular atrophy Sperm count Voice change (deepening) Breast tissue Gynecomastia Testosterone levels Facial hair Menstrual irregularities Clitoral enlargement

Males and Females

Increase Decrease Possible

LDL-C HDL-C Hypertension LDL-C/HDL-C Connective tissue damage Potential for neoplastic liver disease Myocardial damage Aggressiveness, hyperactivity, irritability Myocardial infarction Withdrawal and depression when steroid use stops Impaired thyroid function Acne Altered myocardial structure Peliosis hepatitis 97818_ch23.qxd 8/4/09 4:47 PM Page 545

CHAPTER 23 Special Aids to Exercise Training and Performances 545 drug network as competitors try to circumvent detection. American College of Sports Medicine: Position One such drug, the sympathomimetic amine clenbuterol Stand on Use of Anabolic Steroids (brand names Clenasma, Monores, Novegan, Prontovent, and Based on a comprehensive survey of the world lit- Spiropent) has become popular among athletes because of its erature and a careful analysis of the claims made purported tissue-building, fat-reducing benefits. When a for and against the efficacy of anabolicÐandrogenic bodybuilder discontinues steroid use before competition to steroids in improving human physical perform- avoid detection and possible disqualification, the athlete sub- ance, it is the position of the American College of stitutes clenbuterol to retard loss of muscle mass and facilitate Sports Medicine that: fat burning to achieve the desirable “cut” look. Clenbuterol has particular appeal to female athletes because it does not ¥ AnabolicÐandrogenic steroids in the presence of produce the androgenic side effects of anabolic steroids. an adequate diet and training can contribute to Clenbuterol, one of a group of chemical compounds increases in body weight, often in the lean mus- (albuterol, clenbuterol, salbutamol, salmeterol, terbutaline, cle mass compartment. ␤ formoterol) classified as 2-adrenergic agonists, facilitates ¥ The gains in muscular strength achieved through responsiveness of adrenergic receptors to circulating epineph- high-intensity exercise and proper diet can occur rine, norepinephrine, and other adrenergic amines. A review of by the increased use of anabolicÐandrogenic the available studies of animals (to our knowledge, no human steroids in some individuals. exercise studies have been conducted) indicates that when fed ¥ AnabolicÐandrogenic steroids do not increase to sedentary, growing livestock in dosages in excess of those aerobic power or capacity for muscular exercise. prescribed in Europe for human use for bronchial asthma, ¥ AnabolicÐandrogenic steroids have been associ- clenbuterol increases skeletal and cardiac muscle protein dep- ated with adverse effects on the liver, cardiovascu- osition and slows fat gain (enhanced lipolysis). It also in- lar system, reproductive system, and psychologic creases FFM and decreases fat mass when administered long status in therapeutic trials and in limited research term at therapeutic levels to thoroughbred racehorses.144 on athletes. Until further research is completed, Clenbuterol has been used experimentally in animals to the potential hazards of the use of the counter the effects on muscle of aging, immobilization, malnu- anabolicÐandrogenic steroids in athletes must in- trition, and pathologic tissue-wasting conditions. Under these clude those found in therapeutic trials. ␤ conditions, 2-agonists show specific growth-promoting ac- ¥ The use of anabolicÐandrogenic steroids by ath- tions on skeletal muscle.76,294 For rats, clenbuterol altered letes is contrary to the rules and ethical princi- muscle fiber type distribution, inducing enlargement and in- ples of athletic competition as set forth by many creased proportion of type II muscle fibers.64 A decrease in of the sports governing bodies. The American protein breakdown and increase in protein synthesis accounted College of Sports Medicine supports these ethi- for the animals’ increased muscle size.2,22 cal principles and deplores the use of anabolic- androgenic steroids by athletes. Potential Negative Effects on Muscle, Bone, and Cardiovascular Function (Animal Studies) Specific Risks for Females. Females have additional Female rats treated with clenbuterol (2 mg и kgϪ1) injected concerns about dangers from anabolic steroids. These include subcutaneously versus controls sham-injected with the same virilization (more apparent than in men), disruption of normal volume of fluid carrier each day for 14 days increased muscle growth pattern by premature closure of the plates for bone mass, absolute maximal force-generating capacity, and hyper- growth (also for boys), altered menstrual function, dramatic trophy of fast- and slow-twitch muscle fibers.73 A negative find- increase in sebaceous gland size, acne, hirsutism (excessive ing was hastened fatigue during short-term, intense muscle body and facial hair), and generally irreversible deepening of actions. In contrast, regular exercise combined with clenbuterol the voice, decreased breast size, enlarged clitoris, and hair decreased muscular dystrophy progression in mice, reflected by loss. Serum levels of LH, FSH, progesterone, and estrogens increased muscle force-generating capacity.294 However, the also decline. These may negatively affect follicle formation, group receiving clenbuterol experienced increased muscle ovulation, and menstrual function. The long-term effects on fatigability and cellular deformities not noted in the exercise- reproductive function, including possible sterility, require fur- only group. This negative effect on muscle structure and func- ther clarification. tion may explain findings that clenbuterol treatment negated the beneficial effects of exercise training on endurance perform- 127 Clenbuterol and Other ance, despite increased muscle protein content. Clenbuterol ␤ -Adrenergic Agonists treatment induced muscular hypertrophy in young male rats but 2 also inhibited longitudinal bone growth.149 Negative effects of Extensive, random testing of competitive athletes for steroid clenbuterol and salbutamol affected mechanical properties and use has ushered in a number of steroid “substitutes.” These have microarchitecture of trabecular bone of animals. An increase of appeared on the health food, mail order, and “black market” muscle mass with enhanced bone fragility increases fracture risk 97818_ch23.qxd 8/4/09 4:47 PM Page 546

546 Section 4 Enhancement of Energy Transfer Capacity ␤ 29,30 58 when treated with 2-agonists as part of a doping regimen. performance in two 10-minute cycling trials. Similarly, no ef- The negative effect on bone contraindicates its use for prepubes- fect occurred in power output during a 30-second Wingate test cent and adolescent humans. in nonasthmatic trained cyclists who received 360 ␮g (twice the Echocardiographic evaluations of Standard bred mares normal dose administered by inhaler in 4 measured doses of showed that chronic clenbuterol administration even at low ther- 90 ␮g each) 20 minutes before testing.156 For men without apeutic levels alters the heart’s structural dimensions, which neg- asthma, acute therapeutic (200 ␮g) or supratherapeutic (800 ␮g) atively affects cardiac function.240 Effects occurred whether the doses of inhaled salbutamol had no effect on quadriceps animals exercised or remained inactive. Clenbuterol also caused strength, fatigue, and recovery.67 In other research, twice the aortic enlargement after exercise to a degree that indicated recommended dose of salbutamol (albuterol: 400 mg adminis- increased risk of aortic rupture and sudden death. Clenbuterol tered in four inhalations 20 minutes before exercising) did not treatment when combined with aerobic training blunts the nor- enhance anaerobic power output, endurance performance, venti- mal training-induced increase in plasma volume in Standard bred latory threshold, or dynamic lung function of trained endurance mares; this effect accompanied decreased aerobic exercise per- cyclists.186 The researchers maintained that competitive athletes formance and ability to recover.143 should not be prohibited from these compounds because they provide no ergogenic benefit, yet “normalize” individuals with obstructive pulmonary disorders. Differences in training status Clenbuterol: Not Approved for may explain discrepancies among studies concerning albuterol’s Human Use in the United States effect on short-term power output. Clenbuterol is commonly prescribed abroad as an in- Albuterol’s ergogenic benefit supposedly comes from its ␤ haled bronchodilator to treat obstructive pulmonary disorders. stimulating effects on skeletal muscle 2-receptors to increase ␤ Reported short-term side effects in humans who accidentally muscle force and power. With exercise training, the muscle 2- “overdosed” from eating clenbuterol-tainted meat include: receptors undergo downregulation (become less sensitive to a skeletal muscle tremor, agitation, palpitations, dizziness, nau- given stimulus) from chronic exposure to training-induced sea, muscle cramps, rapid heart rate, and headache. Despite elevations in blood catecholamine levels. This makes the these negative side effects, clenbuterol may benefit humans trained athlete less responsive to a sympathomimetic drug than when used to treat muscle wasting (in disease), forced immo- an untrained counterpart. bilization, and aging. Unfortunately, no data exist for potential toxicity level or its efficacy and long-term safety. Clearly, Growth Hormone: Genetic clenbuterol use cannot be justified or recommended as an Engineering Comes to Sports ergogenic aid. Human growth hormone (GH or hGH), also known as somatotropin, currently competes with anabolic steroids in the Other Adrenergic Agonists illicit market of alleged tissue-building, performance- Research has focused on possible strength-enhancing effects enhancing drugs. The adenohypophysis of the pituitary gland ␤ produces GH, a potent anabolic and lipolytic agent in tissue- of sympathomimetic 2-adrenergic agonists other than clenbuterol. Men with cervical spinal-cord injuries took 80 mg of building processes and growth. Specifically, GH stimulates metaproterenol daily for 4 weeks in conjunction with physical bone and cartilage growth, enhances fatty acid oxidation, and therapy. Increases occurred in estimated muscle cross- reduces glucose and amino acid breakdown. Reduced GH sectional area and elbow flexor and wrist extensor strength secretion accounts for some of the decrease in FFM and compared with a placebo condition.239 Albuterol administra- increase in fat mass that accompanies aging. This condition tion (16 mg и dϪ1 for 3 wk) without exercise training im- reverses somewhat with exogenous recombinant GH supple- proved muscular strength 10 to 15%.167 Therapeutic doses of ments produced by genetically engineered bacteria. Healthy albuterol also facilitated isokinetic strength gains from slow- elderly men who received GH supplements increased FFM 190 speed concentric/eccentric isokinetic training.44 (4.3%) and decreased fat mass (13.1%). Supplementation did not reverse the negative effects of aging on functional measures of muscular strength and aerobic capacity. Men Training State Makes a Difference receiving the supplement also experienced hand stiffness, Animals. Untrained skeletal muscle of animals responds malaise, arthralgias, and lower-extremity edema. One of the ␤ to the effects of 2-adrenergic agonists. The increase in muscle largest studies to date determined the effects of exogenous GH mass with clenbuterol treatment plus exercise training is more over a 6-month period on changes in body composition pronounced in animals without prior training experience than and functional capacity of healthy men and women aged in trained animals that continue training and then receive this mid-60s to late 80s.27 Men who took GH gained 7 pounds of drug.184 lean body mass and reduced a similar amount of fat mass. Women gained about 3 pounds of lean body mass and lost Humans. Some research with humans shows improved 5 pounds of body fat compared with counterparts receiving a muscle power output with albuterol administration.238 However, placebo. Unfortunately, serious side effects afflicted between no ergogenic effect occurred from salbutamol on short-term 24 and 46% of the subjects. These included swollen feet and 97818_ch23.qxd 8/4/09 4:47 PM Page 547

CHAPTER 23 Special Aids to Exercise Training and Performances 547 ankles, joint pain, carpal tunnel syndrome (swelling of tendon synthesis in skeletal muscle, torso and limb circumferences, or sheath over a nerve in the wrist), and development of a dia- muscle function in dynamic and static strength measures betic or prediabetic condition. As in prior research, no effects (TABLE 23.3). The authors attributed the greater increase in occurred for GH treatment on measures of muscular strength whole-body protein synthesis in the GH group to a possible in- or endurance capacity despite increases in lean body mass. crease in nitrogen retention in lean tissue other than skeletal Excessive GH production during skeletal growth pro- muscle—for example, connective tissue, fluid, and noncontrac- duces gigantism, an endocrine and metabolic disorder char- tile protein. acterized by abnormal size or overgrowth of the entire body GH occurs naturally in the body, making ready detection or any of its parts. Excessive hormone production following as an ergogenic substance difficult. Blood markers are cur- growth cessation produces the irreversible disorder acromegaly rently available for screening. Nonprescription GH can only be that presents as enlarged hands, feet, and facial features. obtained on the black market and often in an adulterated form. Medically, children who suffer from kidney failure or who Human cadaver-derived GH (used until May 1985 by U.S. produce insufficient GH receive thrice-weekly biosynthetic physicians to treat children of short stature) greatly increases GH injections until adolescence to help them achieve near- risk for contracting Creutzfeldt-Jakob disease, an infectious, normal size. In young adults with hypopituitarism, GH incurable, and fatal brain-deteriorating disorder. A synthetic replacement therapy improves muscle volume, isometric form of GH (Protoropin and Humantrope), produced by strength, and exercise capacity. genetic engineering, currently treats GH-deficient children. Undoubtedly, child athletes who receive GH believing they gain a competitive edge will suffer increased incidence of gi- No Unanimity Among Researchers gantism, while adults will develop acromegalic syndrome. At first glance, GH use seems appealing to strength and Additional, less obvious side effects include insulin resistance power athletes because at physiologic levels, this hormone stim- that leads to type 2 diabetes, water retention, and carpal tunnel ulates amino acid uptake and muscle protein synthesis while en- compression syndrome. Any potential benefits of GH must be hancing fat breakdown and conserving glycogen reserves. weighed against potential adverse effects.100 Claims that Unfortunately, few well-controlled studies have examined how growth hormone enhances physical performance are not sup- GH supplements affect healthy subjects who undertake exercise ported by the scientific literature. Although the limited avail- training. In one study, six well-trained men maintained a high- able evidence suggests that growth hormone increases lean protein diet while taking either biosynthetic GH or a placebo.63 body mass, it may not improve strength; in addition, it may During 6 weeks of standard resistance training with GH, per- worsen exercise capacity and increase adverse events. More re- centage body fat decreased and FFM increased. No changes in search is needed to conclusively determine the effects of body composition occurred for the group training with the growth hormone on athletic performance.163 placebo. Subsequent investigations failed to replicate these findings. For example, 16 previously sedentary young men who par- DHEA ticipated in a 12-week resistance training program received recombinant human GH supplements (40 ␮g и kgϪ1 и dϪ1) or a Dehydroepiandrosterone (DHEA and its sulfated ester, placebo.293 FFM, total body water, and whole-body protein syn- DHEA sulfate, or DHEAS, the most common hormone in the thesis increased more in the GH recipients. No significant dif- body) is a weak steroid hormone synthesized primarily from ferences emerged between groups in fractional rate of protein cholesterol by the adrenal cortex of primates. The body

TABLE 23.3 • Maximal Force Production of Knee Extensor and Flexor Muscle Groups Before and After Training With or Without Growth Hormone Supplements

Exercise plus Placebo Exercise plus GH

Initial Final % Change Initial Final % Change

Concentric Knee extensors 212 Ϯ 13a 248 Ϯ 10 17 191 Ϯ 11 214 Ϯ 912 Knee flexors 137 Ϯ 11a 158 Ϯ 7 15 122 Ϯ 12 143 Ϯ 617 Isometric Knee extensors 220 Ϯ 13a 252 Ϯ 13 14 198 Ϯ 15 207 Ϯ 75 Knee flexors 131 Ϯ 8a 158 Ϯ 8 20 127 Ϯ 13 140 Ϯ 16 10

From Yarasheski KF, et al. Effect of growth hormone and resistance exercise on muscle growth in young men. Am J Physiol 1992;262:E261. aValues are mean Ϯ SE. Maximum force (N и m) determined using a Cybex dynamometer. Concentric force measured at 60¡ и sϪ1 angular velocity. Isometric force measured at 135¡ of knee extension. The maximum concentric force production of knee flexor and extensor muscles increased significantly in both groups (P Ͻ .05), but these increments and the increments in maximum isometric force production were not greater in the exercise plus GH group. 97818_ch23.qxd 8/4/09 4:47 PM Page 548

548 Section 4 Enhancement of Energy Transfer Capacity

Cholesterol

Delta-5 pathway Delta-4 pathway

Pregnenolone Progesterone

17-Hydroxy- 17-Hydroxy- progenenolone progesterone

Dehydroepi- Androstene- androsterone Estrone dione (DHEA) 4-Androstenediol

5-Androstenediol Testosterone Estradiol

Dihydro- testosterone

Figure 23.5 • Outline of metabolic pathways for dehydroepiandrosterone (DHEA), androstenedione, and related compounds. Directional arrows signify one-way and two-way conversions. Compounds in bold print are DHEA-precursor products currently available on the market.

produces more DHEA than all other known steroids. This levels of DHEA at birth, which then decline sharply (not “mother hormone” has a chemical structure that closely resem- shown). DHEA production increases steadily from age 6 to bles testosterone and estrogen; a small amount of DHEA and re- 10 years (may contribute to the beginning of puberty and sexu- lated prohormone compounds are naturally derived precursors ality), and then rises sharply with peak production (higher in to testosterone or other anabolic steroids. FIGURE 23.5 outlines males than females) between ages 20 and 25 years. In contrast to the major pathways for synthesizing DHEA, androstenedione, the glucocorticoid and mineralocorticoid adrenal steroids, and related compounds. whose plasma levels remain relatively high with aging, DHEA Because DHEA occurs naturally, the FDA exerts no levels undergo a steady decline after age 30. By age 75, the control over its distribution or claims for its action and plasma level averages only about 20% of that in young adults. effectiveness. The Drug Enforcement Administration This low level means that plasma DHEA levels might serve as a (www.usdoj.gov/dea/) does not consider DHEA to be an ana- biochemical marker of biologic aging and disease susceptibility. bolic steroid as defined in section 102(6) of the Controlled Popular reasoning concludes that supplementing with Substances Act (www.usdoj.gov/dea/pubs/csa.html). Instead, DHEA blunts the negative effects of aging by raising plasma DHEA fits the definition of a dietary supplement. levels to more “youthful” concentrations. Many persons sup- The lay press, mail order, Internet, and health food indus- plement with this “natural” hormone just in case it proves try and advertisements tout DHEA as a “superhormone”— beneficial—typically without considering the potential for a Holy Grail that increases testosterone production; protects biologic harm. against cancer, heart disease, diabetes, and osteoporosis; bol- sters the immune system; preserves youth; invigorates sex life; An Unregulated Compound decreases joint pain and fatigue; facilitates lean tissue gain and with Uncertain Safety body fat loss; enhances mood and memory and generally counters the debilitating effects of aging; and extends life. The hor- Appropriate DHEA dosage for humans remains uncer- mone’s detractors consider it the “snake oil” of the twenty-first tain. Concern exists about possible harmful effects on blood century, and WADAhas banned DHEA at zero-tolerance levels. lipids, glucose tolerance, and prostate gland health, particu- FIGURE 23.6 illustrates the generalized trend for plasma larly because medical problems associated with hormone DHEA levels during a lifetime, with six common claims by supplementation often do not appear until years after initia- manufacturers of supplements. Boys and girls have substantial tion of drug use. 97818_ch23.qxd 8/4/09 4:47 PM Page 549

CHAPTER 23 Special Aids to Exercise Training and Performances 549 immune function in middle-aged men and women. Subsequent research evaluated short-term ingestion of 50 mg of DHEA daily on serum steroid hormones and 8 weeks supplementation Peak production (20-25y) (150 mg daily) on resistance-training adaptations in young men.32 Short-term supplementation rapidly increased serum androstenedione (see next section) concentrations but exerted no effect on serum testosterone and estrogen concentrations. Furthermore, long-term DHEA supplementation elevated serum androstenedione levels but did not affect anabolic hormones, serum lipids, liver enzymes, muscular strength, and lean body mass, compared with a placebo for men undergoing similar training. These and similar results verify that relatively low dosages of DHEA do not increase serum testosterone levels, en- DHEA level DHEA hance muscular strength, change muscle and fat cross-sectional areas, or facilitate adaptations to resistance training.196,283 Concern exists about the effect of unregulated long-term DHEA supplementation (particularly at or above 50-mg daily) on bodily function and overall health. Converting DHEA into potent androgens such as testosterone promotes facial hair growth in females and alters normal menstrual function. Like 0 102030405060 70 80 90 100 exogenous anabolic steroids, DHEA lowers HDL-C levels to in- Age (y) crease heart disease risk. Conflicting data concern its effects on Female Male breast cancer risk. Clinicians have expressed fear that elevating plasma DHEA by supplementation might stimulate the growth of otherwise dormant prostate gland tumors or cause benign hy- Claims for DHEA pertrophy of the prostate gland. If cancer exists, DHEA may accelerate its growth. Despite its popularity among exercise • Blunts aging • Facilitates weight loss enthusiasts, no data support an ergogenic effect of exogenous • Boosts immune function DHEA on young adult men and women. • Inhibits development of Alzheimer's disease • Protects against heart disease Androstenedione: Benign Prohormone • Retains and increases muscle mass Nutritional Supplement or Potentially Harmful Drug? Figure 23.6 • Generalized trend for plasma levels of DHEA for men and women over a lifetime. The over-the-counter supplement androstenedione (in addition to norandrostenediol and norandrostenedione, which convert to With humans, cross-sectional observations relating the steroid nandrolone) supposedly does the following: DHEA levels to risk of death from heart disease provided early indirect evidence for a beneficial effect. A high DHEA 1. Stimulates production of endogenous testosterone or level conferred protection in men; for women, however, ele- forms androgen-like derivatives (as shown in Fig. 23.5) vated DHEA increased heart disease risk. Subsequent re- 2. Enables more intense training search showed only a moderate protective association for men 3. Builds muscle mass and no association for women. Studies suggest that DHEA 4. Rapidly repairs tissue injury supplements may provide cardioprotection during aging 133 Found naturally in meat and some plant extracts, an- (more beneficial in men than in women), decrease abdomi- drostenedione is often touted as a prohormone, a metabolite nal fat and improve insulin sensitivity among the elderly, only one step away from the biosynthesis of testosterone. The which could play a role in the prevention and treatment of the National Football League, NCAA, Men’s Tennis Association, metabolic syndrome,274 boost immune function in disease,270 7 and WADA ban its use because they believe it provides unfair and provide antioxidant protection. competitive advantage and may endanger health. In additional research on humans, eight men and eight women (ages 50 to 65 y) received either 100 mg of DHEA or a INTEGRATIVE QUESTION placebo daily for 3 months and the other treatment for the next 3 months.182 All subjects showed a 1.2% increase in lean body Respond to the question: If testosterone, growth mass during DHEA supplementation. Fat mass decreased in hormone, and DHEA occur naturally in the body, men but increased slightly in women. Chemical markers indi- what harm could exist in supplementing with cated improved immune function. These findings suggest some these “natural” compounds? positive effects of exogenous DHEA on muscle mass and 97818_ch23.qxd 8/4/09 4:47 PM Page 550

550 Section 4 Enhancement of Energy Transfer Capacity In the United States in 1994, the FDA developed rules for plasma total and free testosterone concentrations compared marketing androstenedione as a food, not as a drug. By calling with a placebo.78 Androstenedione dosages as high as 300 mg the substance a supplement and avoiding any claims of med- per day have elevated testosterone levels by 34%.155 Chronic ical benefit, savvy marketers and distributors created a androstenedione administration also elevates serum estradiol lucrative business for androstenedione, mostly via Internet and estrone in men and women, perhaps offsetting any poten- sales and over-the-counter at health food stores. An tial anabolic effect. androstenedione-containing chewing gum and steroid lozenge Little scientific evidence supports claims of androstene- that dissolves under the tongue are currently available. dione’s ergogenic effectiveness or anabolic qualities. One study Androstenedione, an intermediate (precursor) hormone systematically evaluated whether short- and long-term an- between DHEA and testosterone, aids the liver in synthesizing drostenedione supplementation elevates blood testosterone other biologically active steroid hormones. Androstenedione is concentrations or enhances muscle size and strength gains dur- normally produced by the adrenal glands and gonads and con- ing resistance training. In one phase of the investigation, young verted to testosterone enzymatically by 17␤-hydroxysteroid adult men received either a single 100-mg dose of androstene- dehydrogenase found in the body’s diverse tissues. It also dione or a placebo containing 250 mg of rice flour. FIGURE 23.7A serves as an estrogen precursor. shows that serum androstenedione rose 175% during the first Research has demonstrated the effectiveness of exoge- 60 minutes following ingestion and then increased further to nous androstenedione for raising testosterone levels. Daily about 350% above baseline values between minutes 90 and oral treatment with 200 mg of 4-androstene-3,17-dione or 270. However, short-term supplementation did not affect serum 200 mg of 4-androstene-3␤,17␤-diol increased peripheral concentrations of either free or total testosterone.

45 40

) 35 –1

L 30 . 25 20 (nmol 15 160 400 ) A ndrostenedione 140 10 –1 L .

0 ) 120 300

–1 100 L . 80 200 45 60 40 (pmol 40 100

) 35 Free testosterone

–1 20 Estradiol (pmol Estradiol

L 30 . 0 0 25 20 (pmol 15 160 400 )

Free testosterone 10 140 –1 L . 0 ) 120 300

–1 100 L . 45 80 200 40 60 (nmol 35 40 100 )

Total testosterone Total 20 Estrone (pmol

–1 30 L

. 0 0 25 0 2468 0 2468 B C 20 Weeks of supplementation Weeks of supplementation

(nmol 15 10 Total testosterone Total 0 Placebo Androstenedione A 0 60 180120 300240360 Time after ingestion (min)

Figure 23.7 • A. Effect of short-term (single-dose) exogenous supplementation with 100 mg of androstenedione or placebo on serum concentrations of androstenedione and free and total testosterone. B. Serum free and total testosterone, and C. serum estradiol and estrone with 300-mg daily supplementation of androstenedione (N ϭ 9) and placebo (N ϭ 10) during 8 weeks of resistance training. (From King DS, et al. Effect of oral androstenedione on serum testosterone and adaptations to resistance training in young men. JAMA 1999;281:2020.) 97818_ch23.qxd 8/4/09 4:47 PM Page 551

CHAPTER 23 Special Aids to Exercise Training and Performances 551 In the experiment’s second phase, 20 young, untrained androstenediol, respectively, except with slight chemical men received 300 mg of androstenedione daily (N ϭ 10) or modification that supposedly enhances anabolic properties 250 mg of a rice flour placebo during weeks 1, 2, 4, 5, 7, and 8 without converting to testosterone but to the steroid nan- of an 8-week total-body resistance-training program. Serum drolone. These modifications should theoretically confer ana- androstenedione levels increased 100% in the androstenedione- bolic effects via the compounds’ direct activation of the supplemented group and remained elevated throughout train- androgen receptors in skeletal muscle. To test this hypothesis, ing. Serum testosterone levels (FIG. 23.7B) remained higher in research evaluated 8 weeks of low-dose norsteroid supple- the androstenedione-supplemented group than the placebo mentation on body composition, girth measures, muscular group before and following supplementation. Free and total strength, and mood states of young adult, resistance-trained testosterone levels remained unaltered for both groups. Serum men.266 The men received 100 mg of 19-nor-4-androstene- estradiol and estrone concentrations only increased during 3,17-dione plus 56 mg of 19-nor-4-androstene-3,17-diol training for the supplemented group, suggesting increased (156 mg total norsteroid per day) or a multivitamin placebo. aromatization of the ingested androstenedione to estrogens Each subject did resistance training 4 days weekly for the (FIG. 23.7C). Resistance training increased muscle strength duration of the study. Norsteroid supplementation provided and lean body mass and reduced body fat for both groups, but no additional effect on any of the body composition or exer- no synergistic effect emerged for the group supplemented cise performance variables. with androstenedione. The supplement produced a 12% HDL- C reduction after only 2 weeks, which remained lower for the Competitive Athletes Beware 8 weeks of training and supplementation. Serum liver enzyme concentrations stayed within normal limits for both groups Elite athletes who take androstenedione can fail a urine throughout the experiment. test for the banned anabolic steroid nandrolone. This occurs Contrary to marketing and advertising claims, research to because the supplement often contains contaminates with date indicates that prohormone nutritional supplements (DHEA, trace amounts (as low as 10 ␮g) of 19-norandrosterone, the androstenedione, androstenediol, and other prohormone com- standard marker for nandrolone use. Many androstenedione pounds) do not produce anabolic or ergogenic effects in men.225 preparations are grossly mislabeled. Analysis of nine different Research findings also indicate no effect of androstenedione brands of 100-mg doses indicate wide fluctuations in overall supplementation on basal serum concentrations of testosterone content ranging from zero to 103 mg of androstenedione, with or training response for muscle size and strength and body com- one brand contaminated with testosterone.47 position. The potential negative effects of the HDL-C reduction on overall heart disease risk and the elevated serum estrogen INTEGRATIVE QUESTION levels on risk of gynecomastia and possibly pancreatic and other cancers cause concern. Findings must be viewed within the con- Outline the points you would make in a talk to text of this specific study, because subjects took smaller a high school football team concerning whether amounts of androstenedione than routinely consumed for they should consider using performance- ergogenic purposes (500 to 1200 mg per day). enhancing chemicals and hormones.

Summary of Research Findings Concerning Androstenedione Amino Acid Supplementation ¥ Conflicting findings concerning elevation of plasma testosterone concentrations An emerging trend involves using nutrition as a “legal” alter- ¥ No favorable effect on muscle mass native to activate the body’s normal anabolic mechanisms. ¥ No favorable effect on muscular performance Highly specific dietary changes supposedly create a hormonal ¥ No favorable alterations in body composition milieu that facilitates protein synthesis in skeletal muscle. ¥ Elevates a variety of estrogen subfractions More than 100 companies in the United States promote such ¥ No favorable effect on muscle protein synthesis alleged ergogenic stimulants. Weightlifters, bodybuilders, and or tissue anabolism fitness enthusiasts regularly use amino acid supplements, be- ¥ Impairs blood lipid profile in healthy men lieving they boost the body’s natural production of testos- ¥ Increases likelihood of a positive steroid test result terone, GH, insulin, or insulin-like growth factor I (IGF-I) and so improve muscle size and strength and decrease body fat. The rationale for nutritional ergogenic stimulants comes from the clinical use of amino acid infusion or ingestion to regulate anabolic hormones in deficient patients. A Modified Version Research on healthy subjects does not provide convinc- Norandrostenedione and norandrostenediol are nor- ing evidence for an ergogenic effect of a generalized regular steroid compounds available over the counter in the United intake of amino acid supplements above the recommended States. They are chemically similar to androstenedione and protein intake on hormone secretion, training responsiveness, 97818_ch23.qxd 8/4/09 4:47 PM Page 552

552 Section 4 Enhancement of Energy Transfer Capacity or exercise performance. In studies with appropriate design immediately following and then 2 hours following the train- and statistical analysis, oral supplements of arginine, lysine, ing session. Each nutritive supplement produced a hormonal ornithine, tyrosine, and other amino acids, either singly or in environment (elevated plasma insulin and GH concentrations) combination, produced no positive effect on GH levels,57,154 during recovery more conducive to protein synthesis and insulin secretion,34,90 diverse measures of anaerobic power,89 muscle tissue growth than the placebo condition. Subsequent á 248 or all-out running performance at VO2max. Elite junior research showed that proteinÐcarbohydrate supplementation weightlifters who regularly supplemented with all 20 amino before and immediately following resistance training altered acids did not improve physical performance or change resting the metabolic and hormonal responses to 3 consecutive days or exercise levels of testosterone, cortisol, or GH.95 Thus, reg- of heavy resistance training.151 Changes in the immediate re- ular intake of amino acids in the quantities recommended in covery period included increased concentrations of glucose, commercial supplements does not benefit the hormonal pro- insulin, GH, and IGF-I and decreased blood lactate concentra- file, body composition and muscle size, or exercise perform- tion. Such data provide indirect evidence for a possible train- ance. Additionally, indiscriminate consumption of amino acid ing benefit (e.g., enhanced glycogen and protein synthesis in supplements at dosages considered pharmacologic rather than recovery) from increasing carbohydrate and/or protein intake nutritional raises the possibility of direct toxic effects or the immediately after a workout. creation of an amino acid imbalance. A recent study compared the effects of supplement timing (i.e., the strategic consumption of protein and carbohydrate before and/or after each workout) compared with supplementa- Specific Timing of Intake May tion in the hours not close to the workout on muscle fiber Stimulate an Anabolic Effect hypertrophy, muscular strength, and body composition. Manipulation and timing of intake of nutritional variables Resistance-trained men matched for strength were placed in in the immediate pre- and postexercise periods can affect the one of two groups; one group consumed a supplement (1g per responsiveness to resistance training via mechanisms that alter kg body weight) containing proteinÐcreatineÐglucose immedi- nutrient availability, enzyme activity, circulating metabolites ately before and after resistance training, while the other and hormonal secretions, interactions with receptors on target group received the same supplement dose in the morning and tissues, and gene translation and transcription.82,147,260,277 late evening of the workout day. Measurements of body com- Resistance training stimulates protein synthesis and protein position by dual energy X-ray absorptiometry (DXA; see degradation in exercised muscle fibers. Muscle hypertrophy Chapter 28), strength (1-RM), and muscle fiber type, cross- occurs when a net increase in protein synthesis results from a sectional area, contractile protein, creatine, and glycogen con- shift in the body’s normal dynamic state of synthesis and degra- tent from vastus lateralis muscle biopsies took place the week dation. The normal hormonal milieu (e.g., insulin and GH lev- prior to and immediately after a 10-week training program. els) in the period following resistance exercise stimulates the Supplementation in the immediate preÐpost exercise period muscle fiber’s anabolic processes while inhibiting muscle pro- produced a greater increase in lean body mass and 1-RM tein degradation. Dietary modifications that increase amino strength in two of three measures (FIG. 23.8). Body composi- acid transport into muscles, raise energy availability, or in- tion changes were supported by greater increases in muscle crease anabolic hormones, particularly insulin, should theoreti- cross-sectional area of the type II muscle fibers and contrac- cally increase the rate of anabolism and/or depress catabolism. tile protein content. These findings indicate that supplement Either effect would create a positive body protein balance to timing provides a simple but effective strategy to enhance the improve muscle growth and strength. desired adaptations from resistance training.

CarbohydrateÐProtein-Creatine Supplementation in Postexercise Glucose Augments Protein Balance Recovery Augments Hormonal Response to Resistance After Resistance-Training Workouts. Research with post- Exercise. Studies of hormonal dynamics and protein an- exercise glucose ingestion complements the previously de- abolism indicate a transient but potential ergogenic effect (up scribed studies of carbohydrateÐprotein supplementation to 4-fold increase in protein synthesis)208 of carbohydrate following resistance training. Healthy men familiar with and/or protein supplements consumed prior to259,291or imme- resistance training performed 8 sets of 10 repetitions of uni- diately following a resistance exercise workout.25,129,176 lateral knee extensor exercise at 85% of maximum strength Supplementation in the immediate postexercise period may in a placebo-controlled, randomized, double-blind trial. also enhance repair and synthesis of muscle proteins follow- Immediately after the exercise session and 1 hour later, ing aerobic exercise.157,158 subjects received either a glucose supplement (1.0 g per kg Drug-free male weightlifters with at least 2 years of body mass) or a placebo of Nutrasweet. Measurements training experience consumed carbohydrate and protein sup- consisted of (1) urinary 3-methylhistidine excretion (3-MH) plements immediately after a standard workout.48 Treatment as a marker of muscle protein degradation, (2) vastus later- included either (1) placebo of pure water or a supplement of alis muscle incorporation rate for the amino acid leucine 13 (2) carbohydrate (1.5 g per kg body mass), (3) protein (1.38 g (L-[l- C]leucine) to indicate protein synthesis, and (3) urinary per kg body mass), or (4) carbohydrateÐprotein (1.06 g carbo- nitrogen excretion to reflect protein breakdown. FIGURE 23.9A hydrate plus 0.41 g protein per kg body mass) consumed and B shows that glucose supplementation reduced myofibrillar 97818_ch23.qxd 8/4/09 4:47 PM Page 553

CHAPTER 23 Special Aids to Exercise Training and Performances 553 protein breakdown as reflected by decreased excretion of 3-MH and urinary nitrogen. Although not statistically signif- 3.5 * icant, glucose supplementation also increased the rate of 3 leucine incorporation into the vastus lateralis over the 2.5 10-hour postexercise period (Fig. 23.8C). These alterations 2 indicated that the supplemented condition produced a more positive body protein balance after exercise. The beneficial 1.5 effect of a postexercise high-glycemic glucose supplementa- 1 tion most likely occurred from increased insulin release with

kg * 0.5 glucose intake, which should enhance muscle protein bal- 0 ance in recovery. –0.5 One should view the effects of immediate postexercise carbohydrate and/or protein supplementation in perspective. –1 The question awaiting answer concerns the degree that any –1.5 transient (albeit positive) change in hormonal milieu favoring –2 anabolism and net protein synthesis caused by postexercise LBM Fat mass Body fat % A dietary maneuvers contributes to long-term muscle growth Body composition and strength enhancement. In this regard, no effect occurred 25 from immediate postexercise ingestion of an amino acidÐ * carbohydrate mixture on muscular strength or size gains of 20 older men who did 12-weeks of knee extensor resistance training.102 Differences in study population, criterion vari- 15 ables, specific amino acid mixtures, overall diet composition, * and subjects’ age may account for future discrepancies in re- kg 10 search findings.

5 Dietary Lipid May Affect Hormonal Milieu. The diet’s lipid content can modulate resting neuroendocrine 0 homeostasis to modify tissue synthesis and training respon- Bench press Squat Dead-lift B siveness. Research evaluated the effects of an intense re- Muscular strength sistance-exercise bout on postexercise plasma testosterone. 1400 In agreement with prior research, testosterone levels in- ** creased 5 minutes postexercise. A more impressive finding 1200 was a close association between the macronutrient compo- 1000 sition of the individual’s regular diet and resting testos- 2 800 terone levels. TABLE 23.4 shows that the quantity and Um percentage of dietary macronutrients correlated with preex- 600 ercise testosterone concentrations. Dietary lipid and satu- 400 rated and monounsaturated fatty acid levels best predicted 200 testosterone concentrations at rest—lower levels of each of these dietary components accompanied lower resting levels 0 of testosterone. These findings support prior studies that Type I Type IIa Type IIx C showed that a low-fat diet (~20% fat) produced lower Muscle fiber cross-sectional area testosterone levels than a diet with higher lipid content (~40% fat).206,258 The diet’s protein percentage correlated * Statistically significant greater inversely with resting testosterone levels—higher dietary Pre/Post Mor/Eve change compared with Mor/Eve protein related to lower testosterone levels (see Table 23.4). Many resistance-trained athletes consume considerable di- Figure 23.8 • Effects of receiving a supplement (1 g per kg etary protein, so the implications of this association for the of body weight) or protein, creatine, and glucose immediately before and after resistance (Pre/Post) exercise training or in training response remain unresolved. If a low dietary lipid the early morning (Mor) or late evening (Eve) of the training intake decreases resting testosterone levels, then individu- day on changes in (A) body composition (B) 1-RM strength als who typically consume low-fat diets (e.g., vegetarians, and (C) muscle cross-sectional area (From Cribb PJ, Hayes A. dancers, gymnasts, wrestlers) may experience a diminished Effects of supplement timing and resistance exercise on training response. Furthermore, athletes who show low skeletal muscle hypertrophy. Med Sci Sports Exerc plasma testosterone levels from overtraining may benefit 2006;38:1918.) from changing their diet’s macronutrient composition to lower protein and higher fat. 97818_ch23.qxd 8/4/09 4:47 PM Page 554

554 Section 4 Enhancement of Energy Transfer Capacity

TABLE 23.4 • Relationships Between Preexercise Testosterone Concentration and Selected Nutritional Variables Correlation with Nutrient Testosteronea

Energy, kJ Ϫ0.18 Protein, %b Ϫ0.71* CHO, %b Ϫ0.30 Lipid, %b 0.72* SFA, g 1000 kCalϪ1 и dϪ1 0.77† MUFA, g 1000 kCalϪ1 и dϪ1 0.79‡ PUFA, g 1000 kCalϪ1 и dϪ1 0.25 Cholesterol, g 1000 kCalϪ1 и dϪ1 0.53 PUFA/SFA Ϫ0.63‡ 130 Dietary fiber, g 1000 kCalϪ1 и dϪ1 Ϫ0.19

) Protein/CHO Ϫ0.59‡ –1 120 Protein/lipid 0.16 * CHO/lipid 0.16

lhistidine 110 a Pearson product-moment correlations. b

g creatine Nutrient percentage values expressed as percentage of total energy . per day. 100 *P Յ .01; †P Յ .005; ‡P Յ .05.

3-Meth y SFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, (μmol polyunsaturated fatty acids; CHO, carbohydrate. 0 From Volek JS, et al. Testosterone and cortisol in relationship to dietary A nutrients and resistance exercise. J Appl Physiol 1997;82:49. 16 14 ) –1 12 * Amphetamines 10 Amphetamines, or “pep pills,” comprise a group of pharma- 8 cologic compounds that exert powerful stimulating effects on 6

g creatine central nervous system function. Amphetamine (Benzedrine) .

Urea nitrogen 4 and dextroamphetamine sulfate (Dexedrine) have frequently (g 2 been used by athletes. Amphetamines exert sympathomimetic 0 effects—their action mimics epinephrine and norepinephrine B (sympathomimetic)—to increase blood pressure, heart rate, 0.035 cardiac output, breathing rate, metabolism, and blood glucose. Five to 20 mg of amphetamine usually exerts its effect 0.030 for 30 to 90 minutes after ingestion, although its influence 0.025 often persists for longer. Amphetamines increase alertness, 0.020 ) difference

–1 0.015 h .

leg control 0.010 Figure 23.9 • Effects of glucose (1.0 g per kg body mass)

w een leg exercise and 0.005 versus Nutrasweet placebo, ingested immediately after

MPS (% exercise and 1 hour later, on protein degradation reflected by

bet 0.000 24-hour urinary output of (A) 3-methylhistidine, (B) urinary C urea nitrogen, and (C) rate of muscle protein synthesis (MPS) measured by vastus lateralis muscle incorporation of leucine * Statistically significant compared 13 Glucose Placebo to placebo condition (L-[l- C]). Bars for MPS indicate difference between exercise and control leg for glucose and placebo conditions. (From Roy BD, et al. Effect of glucose supplement timing on protein metabolism after resistance training. J Appl Physiol 1997;82:1882.) 97818_ch23.qxd 8/4/09 4:47 PM Page 555

CHAPTER 23 Special Aids to Exercise Training and Performances 555

IN A PRACTICAL SENSE Nutrient Timing to Optimize Muscle Response to Resistance Training

An evidence-based nutritional approach may enhance the quality state to accentuate gains in muscle mass and muscle strength. of resistance training and facilitate muscle growth and strength de- The first several hours (rapid segment) of this phase is geared to velopment. This easy-to-follow new dimension to sports nutrition maintaining increased insulin sensitivity and glucose uptake to emphasizes not only the specific type and mixture of nutrients but maximize glycogen replenishment. It also speeds elimination of also the timing of nutrient intake. Its goal is to blunt the catabolic metabolic wastes via increased blood flow and stimulates tissue state (release of hormones glucagon, epinephrine, norepinephrine, repair and muscle growth. The next 16 to 18 hours (sustained cortisol) and activate the natural muscle-building hormones (testos- segment) maintains a positive nitrogen balance. This occurs with terone, growth hormone, IGF-1, insulin) to facilitate recovery from a relatively high daily protein intake (between 0.91 and 1.2 g of exercise and maximize muscle growth. Three phases for optimizing protein per pound of body weight) that fosters sustained but specific nutrient intake are outlined: slower muscle tissue synthesis. An adequate carbohydrate intake emphasizes glycogen replenishment. 1. The energy phase enhances nutrient intake to spare muscle glycogen and protein, enhance muscular endurance, limit im- The recommended growth phase supplement contains the fol- mune system suppression, reduce muscle damage, and facilitate lowing nutrients: 14 g of whey protein, 2 g of casein, 3 g of leucine, recovery in the postexercise period. Consuming a carbohydrate– 1 g of glutamine, and 2 to 4 g of high-glycemic carbohydrates. protein supplement in the immediate preexercise period and during exercise extends muscular endurance; the ingested pro- Ivy J, Portman R. Nutrient timing: the future of sports nutrition. New tein promotes protein metabolism, thus reducing demand for Jersey: Basic Health Publications, 2004. amino acid release from muscle. The carbohydrates consumed Crigg PJ, Hayes A. Effects of supplement timing and resistance exer- during exercise suppress release of cortisol. This blunts the sup- cise on skeletal muscle hypertrophy. Med Sci Sports Exerc pressive effects of exercise on immune system function and 2006;38:1918. lessens the use of branched-chain amino acids generated by protein breakdown for energy. The recommended energy phase supplement contains the following nutrients: 20 to 26 g of high-glycemic carbohydrates (glucose, sucrose, maltodextrin), 5 to 6 g of whey protein (rapidly digested, high-quality protein separated from milk in the cheese-making process), 1 g of leucine; 30 to 120 mg of vitamin C, 20 to 60 IU of vitamin E, 100 to 250 mg of sodium, 60 to 100 mg of potassium, and 60 to 220 mg magnesium. Ingestion of the more slowly digested whole protein casein after exercise produces similar increases in muscle protein net balance and a short-term net muscle protein synthesis compared with whey protein. 2. The anabolic phase consists of the 45-minute postexercise metabolic window—a period of enhanced insulin sensitivity for muscle glycogen replenishment and repair and synthesis of muscle tissue. This shift from catabolic to anabolic state occurs largely by blunting the action of the catabolic hormone cortisol and increasing the anabolic, muscle-building effects of the hormone insulin by consuming a standard high-glycemic carbohydrate– protein supplement in liquid form (e.g., whey protein and high-glycemic carbohydrates). In essence, the high-glycemic carbohydrate consumed postexercise serves as a nutrient acti- vator to stimulate insulin release, which, in the presence of amino acids, increases muscle tissue synthesis and decreases protein degradation. The recommended anabolic phase supplement profile contains the following nutrients: 40 to 50 g of high-glycemic carbohydrates (glucose, sucrose, maltodextrin), 13 to 15 g of whey protein, 1 to 2 g of leucine; 1 to 2 g of glutamine, 60 to 120 mg of vitamin C, and 80 to 400 IU of vitamin E. 3. The growth phase extends from the end of the anabolic phase to the beginning of the next workout. It represents the time period to maximize insulin sensitivity and maintain an anabolic 97818_ch23.qxd 8/4/09 4:47 PM Page 556

556 Section 4 Enhancement of Energy Transfer Capacity

TABLE 23.5 • Effects of Amphetamines on Athletic Performance Study Dose (mg) Experiment Effect of Amphetamines

(1) 10Ð20 Two all-out treadmill runs with 10-min rest between runs None Consecutive 100-yd swims with 10-min rest intervals None 220Ð440-yd swims for time None 220-yd track runs for time None 100-yd to 2-mile track runs for time None (2) 10 Bench stepping to fatigue carrying weights equal to None one-third body mass, 3 times with 3-min rest intervals (3) 5 100-yd swim for speed None (4) 15 All-out treadmill runs None á (5) 10 Stationary cycling at work rates of 275Ð2215 None on submaximal or maximal VO2, kg-m и minϪ1 for 25Ð35 min followed by heart rate, ventilation volume, or blood a treadmill run to exhaustion lactate; time on the bicycle and treadmill increased significantly (6) 20 Reaction and movement time to a visual stimulus None; subjective feelings of alertness or lethargy unrelated to reaction or movement time (7) 5 Psychomotor performance during a simulated Enhanced performance and lessened fatigue; airplane flight if preceded by secobarbital (barbiturate), performance decreased

1. Karpovich PV. Effect of amphetamine sulfate on athletic performance. JAMA 1959;170:558. 2. Foltz EE, et al. The influence of amphetamine (Benzedrine) sulfate and caffeine on the performance of rapidly exhausting work by untrained subjects. J Lab Clin Med 1943;28:601. 3. Haldi J, Wynn, W. Action of drugs on efficiency of swimmers. Res Q 1959;17:96. 4. Golding LA, Barnard RJ. The effects of d-amphetamine sulfate on physical performance. J Sports Med Phys Fitness 1963;3:221. 5. Wyndham CH, et al. Physiological effects of the amphetamines during exercise. S Afr Med J 1971;45:247. 6. Pierson WR, et al. Some psychological effects of the administration of amphetamine sulfate and meprobamate on speed of movement and reaction time. Med Sci Sports 1961;12:61. 7. McKenzie RE, Elliot LL. Effects of secobarbital and D-amphetamine on performance during a simulated air mission. Aerospace Med 1965;36:774.

wakefulness, and capacity to perform work by depressing the 4. Inhibition or suppression of the body’s normal sensation of muscle fatigue. The deaths of two famed cy- mechanisms for perceiving and responding to clists in the 1960s during competitive road racing were at- pain, fatigue, or heat stress jeopardizes health and tributed to amphetamine use. In one of these deaths in 1967, safety. British Tour de France rider Tom Simpson overheated and 5. Effects of prolonged intake of high doses remain suffered a fatal heart attack during the ascent of Mont unknown. Ventoux in Provence. Amphetamine Use and Exercise Performance

Dangers of Amphetamines TABLE 23.5 summarizes the results of seven experiments on amphetamines and physical performance. In general, am- Amphetamine use in athletics makes little sense for the phetamines did not affect exercise capacity or performance of following five reasons: simple psychomotor tasks. 1. Regular use can lead to either physiologic or emo- Athletes take amphetamines to “get up” for the event and tional drug dependency. This causes a cyclical re- keep psychologically ready to compete. The day or evening liance on “uppers” (amphetamines) or “downers” before a contest, competitors often become nervous and irrita- (barbiturates)—the barbiturates reduce or tranquilize ble and have difficulty relaxing. Under these circumstances, a the “hyper” state brought on by amphetamines. barbiturate induces sleep. The athlete then regains the hyper 2. General side effects include headache, tremulous- condition by popping an “upper” prior to competition. WADA ness, agitation, fever, dizziness, and confusion, all of and international sport-governing groups disqualify athletes which negatively affect sports performance that for amphetamine use. Ironically, most research indicates that requires rapid reaction and judgment and a high level amphetamines do not enhance physical performance. Perhaps of steadiness and mental concentration. their greatest influence lies in the psychologic realm; athletes 3. Larger doses are required to achieve the same effect be- are easily convinced that any supplement augments perform- cause drug tolerance increases with prolonged use; this ance. A placebo containing an inert substance often produces can aggravate and precipitate cardiovascular disorders. similar results! 97818_ch23.qxd 8/4/09 4:47 PM Page 557

CHAPTER 23 Special Aids to Exercise Training and Performances 557 Caffeine Caffeine benefits maximal swimming performance. In a double-blind, cross-over research design, seven male and four Caffeine represents a possible exception to the general rule female competent distance swimmers (Ͻ25 min for 1500 m) against taking stimulants for ergogenic effects. Caffeine’s consumed caffeine (6 mg и kg body massϪ1) 2.5 hours before classification and prior regulatory status depend on its use as swimming 1500 m. FIGURE 23.10 shows that split times im- either a drug (over-the-counter for migraine headaches), food proved with caffeine for each 500-m of the swim. Swim time (in coffee and soft drinks), or dietary supplement (alertness averaged 1.9% faster with caffeine than without it (20:58.6 products). The most widely consumed behaviorally active vs. 21:21.8). Enhanced performance with caffeine associated substance in the world, caffeine belongs to a group of lipid- with a lower plasma potassium concentration before exercise soluble purines (proper chemical name: 1,3,7-trimethylxan- and higher blood glucose levels at the end of the trial. These thine) found naturally in coffee beans, tea leaves, chocolate, responses suggest a possible caffeine effect on electrolyte bal- cocoa beans, and cola nuts and often added to carbonated bev- ance and glucose availability. erages and nonprescription medicines (TABLE 23.6). For coffee consumption, this translates to a total of over 500 million cups No DoseÐResponse Relationship. FIGURE 23.11 illus- of coffee consumed daily! Sixty-three plant species contain trates the effects of preexercise caffeine intake on endurance caffeine in their leaves, seeds, or fruits. In the United States, time of nine trained male cyclists. Subjects received a placebo 75% (14 million kg) of caffeine intake (per capita, 150 mg и Ϫ or a capsule containing 5, 9, or 13 mg of caffeine per kg of d 1) comes from coffee (3.5 kg per person per year), 15% body mass 1 hour before cycling at 80% of maximal power from tea, and the remainder from the other items listed in output on a Vá O test. All caffeine trials showed a 24% im- Table 23.6. Depending on preparation, one cup of brewed 2max provement in performance with no additional benefit from coffee contains between 60 and 150 mg of caffeine, instant Ϫ caffeine quantities above 5 mg и kg body mass 1. coffee about 100 mg, brewed tea between 20 and 50 mg, and caffeinated soft drinks about 50 mg. For comparison, 2.5 cups of percolated coffee contain 250 to 400 mg, or generally be- Proposed Mechanism for Ergogenic Effect tween 3 and 6 mg per kg of body mass. The intestinal tract absorbs caffeine rapidly; peak plasma A precise explanation for the ergogenic boost from caf- concentration is reached within 1 hour. It also clears from the feine remains elusive. The ergogenic effect of caffeine (or body relatively quickly, taking about 3 to 6 hours for blood related methylxanthine compounds) in intense endurance caffeine concentrations to decrease by one-half, compared exercise has generally been attributed to facilitated fat use as with about 10 hours for the stimulant methamphetamine. an exercise fuel, thus sparing carbohydrate reserves. In the quantities usually administered to humans, caffeine probably affects metabolism in either of two ways: (1) directly on Ergogenic Effects adipose and peripheral vascular tissues or (2) indirectly by Drinking 2.5 cups of regularly percolated coffee up to stimulating epinephrine release from the adrenal medulla. 1 hour before exercising often extends endurance in strenuous Epinephrine then acts as an antagonist of the adenosine re- aerobic exercise under laboratory conditions; it also improves ceptors on adipocyte cells, which normally repress lipolysis. higher intensity, shorter duration exercise, muscular strength and Caffeine’s inhibition of adenosine receptors increases cellu- power in prolonged exercise, cognitive performance and complex lar levels of the second messenger cyclic 3Ј,5Ј-adenosine cognitive ability, and team sport performance.68,74,124,233,252 Elite monophosphate or cyclic AMP. Cyclic AMP then activates distance runners who consumed 10 mg of caffeine per kg of hormone-sensitive lipases to promote lipolysis; this effect body mass immediately before a treadmill run to exhaustion causes the release of free fatty acids (FFAs) into the plasma. improved performance time compared with placebo or control Elevated FFA levels increase fat oxidation, thus conserving conditions.93 Ergogenic effects during exhaustive exercise at liver and muscle glycogen to benefit intense endurance á и Ϫ1 80% VO2max that follows a 5-mg kg caffeine dose are exercise. maintained 5 hours later in a subsequent exercise challenge.17 Caffeine’s ergogenic effects also appear unrelated to Thus, no need exists to ingest an additional dose to maintain hormonal or metabolic changes. This suggests a possible high blood caffeine levels and ergogenic effects during subse- direct action of caffeine on specific tissues, including the quent exercise within 5 hours. Furthermore, caffeine ingestion nervous system. Caffeine and its metabolites readily cross does not impede glycogen resynthesis with carbohydrate sup- the bloodÐbrain barrier to produce analgesic effects on the plementation after extreme depletion of muscle glycogen.15 central nervous system, potentially reducing the perception Data presented in “Focus on Research,” page 560, show of effort during exercise. Caffeine enhances motoneuronal that subjects performed on average 90.2 minutes of exercise excitability to facilitate motor unit recruitment. The stimu- with caffeine and 75.5 minutes without it. Consuming caffeine lating effects of caffeine do not occur from its direct action before exercise increased fat catabolism and reduced carbohy- on the central nervous system. Instead, caffeine acts indi- drate oxidation during exercise. The ergogenic effect of rectly by blocking the receptors for adenosine (discussed caffeine also applies to exercise performed at high ambient earlier) that also serve a neuromodulator function to calm temperatures.55 brain and spinal cord neurons. The following four factors 97818_ch23.qxd 8/4/09 4:47 PM Page 558

558 Section 4 Enhancement of Energy Transfer Capacity

TABLE 23.6 • Caffeine Content of Common Foods, Beverages, and Over-the-Counter Medications Beverages and Food Over-the-Counter Products

Caffeine Caffeine Substance Content (mg) Substance Content (mg)

Coffee Cold Remedies Coffee, Starbucks, grande, 16oz 550 Dristan Coryban-D, Triaminicin, Sinarest 30Ð31 Coffee, Starbucks, tall, 12 oz 375 Excedrin 65 Coffee, Starbucks, short, 8 oz 250 Actifed, Contac, Comtrex, Sudafed 0 Coffee, Starbucks, Americano, tall, 12 oz 70 Diuretics Coffee, Starbucks, latte or 70 Aqua-ban 200 cappuccino, grande, 16 oz Pre-Mens Forte 100 Brewed, drip method 110Ð150 Pain Remedies Brewed, percolator 64Ð124 Vanquish 33 Instant 40Ð108 Anacin; Midol 32 Expresso 100 Aspirin, any brand; Bufferin, Tylenol, Excedrin PM 0 Decaffeinated, brewed or instant; Sanka 2Ð5 Stimulants Tea, 5-oz cupa Vivarin tablet, NoDoz maximum-strength 200 Brewed, 1 min 9Ð33 caplet, Caffedrine Brewed, 3 min 20Ð46 NoDoz tablet 100 Brewed, 5 min 20Ð50 Energets lozenges 75 Iced tea, 12 oz; instant tea 12Ð36 Weight control aids Chocolate Dexatrim, Dietac 200 Baker’s semi-sweet, 1 oz; Baker’s 13 1 Prolamine 140 chocolate chips, ⁄4 cup b Cocoa, 5-oz cup, made from mix 6Ð10 Pain drugs Milk chocolate candy, 1 oz 6 Cafergot 100 Sweet/dark chocolate, 1 oz 20 Migrol 50 Baking chocolate, 1 oz 35 Fiornal 40 Chocolate bar, 3.5 oz 12Ð15 Darvon compound 32 Jello chocolate fudge mousse 12 Ovaltine 0 Candy Pit Bull Energy Bar (1 barÐ2 oz) 165 Crackheads (1 boxÐ1.3 oz) 120 Blitz energy gum (2 pieces) 110 Jolt gum (1 piece) 60 Snickers Charged (1 barÐ2 oz) 60 Jelly Belly Extreme Sports Beans (14 piecesÐ1 oz) 50 Warp Energy Mints (10) 50 VoJo Extreme Energy Mints (4) 40 Headshot Energy (1 barÐ1.8 oz) 20 Soft Drinks Sugar-Free Mr. Pibb 59 Mellow Yellow, Mountain Dew 53Ð54 Tab 47 Coca Cola, Diet Coke, 7-Up Gold 46 Shasta-Cola, Cherry Cola, Diet Cola 44 Dr. Pepper, Mr. Pibb 40Ð41 Dr. Pepper, sugar free 40 Pepsi Cola 38 Diet Pepsi, Pepsi Light, Diet RC, RC Cola, Diet Rite 36 Energy drinks Jolt (23.5 oz) 280 Rockstar—Punched, Roasted, or Zero Carb 240 Arizona Green Tea Energy or SoBe No Fear1 170 Rockstar—Juiced, Original, or Sugar Free 160 AMP, Full Throttle, Glacéau Vitamin 150 Energy, or Monster1 SoBe Adrenaline Rush—Sugar Free or regular 150 Nestea Enviga (12 oz) or BAWLS 100 TAB (10.5 oz) or SoBe Essential 95 Red Bull—regular or Sugar Free (8.3 oz) 80 Glacéau Vitamin Water, Energy (20 oz) 50 Propel Invigorating Waters (20 oz) 50

Data from product labels and manufacturers and Nation Soft Drink Association. a Brewing tea or coffee for longer periods slightly increases the caffeine content. b Prescription, 1 oz or 30 mL. 97818_ch23.qxd 8/4/09 4:47 PM Page 559

CHAPTER 23 Special Aids to Exercise Training and Performances 559 3. Facilitate nerve transmission 4. Increase ion transport within the muscle 448 444 Inconsistent Effects. Prior nutrition partly accounts for ) 440 why individual differences exist in exercise response after –1 436 consuming caffeine. Those who normally consume a high- 432 carbohydrate diet show a depressed effect for caffeine on FFA

500 m 428 285 . mobilization. Individual differences in caffeine sensitivity, 424 tolerance, and hormonal response from short- and long-term 420 patterns of caffeine consumption also affect this drug’s

Time (s 416 ergogenic qualities. Interestingly, the ergogenic effects of caf- 412 feine are less for caffeine in coffee than for an equivalent dose 408 in capsule form.106 Apparently, components in coffee counteract caffeine’s actions. Beneficial effects do not occur consis- 500 1000 1500 tently in habitual caffeine users. This indicates that an athlete Distance (m) should consider “caffeine tolerance” rather than assume that caffeine provides a consistent benefit to all people. From a practical standpoint, the athlete should omit caffeine-contain- Placebo Caffeine ing foods and beverages 4 to 6 days before competition to op- 269 Figure 23.10 • Split times for each 500 m of a 1500-m time timize caffeine’s potential for ergogenic effects. trial with caffeine and placebo. Caffeine produced significantly faster split times. (From MacIntosh BR, Wright BM. Caffeine Effects on Muscle ingestion and performance of a 1500-metre swim. Can J Appl Physiol 1995;20:168.) Caffeine acts directly on muscle to enhance exercise capacity, particularly repeated submaximum muscle actions.178,226,264 A double-blind research design evaluated 70 voluntary and electrically stimulated muscle actions under “caffeine-free” conditions and following oral administration 60 of 500 mg of caffeine.164 Electrically stimulating the motor nerve allowed the researchers to remove central nervous 50 system control and quantify caffeine’s direct effects on 40 skeletal muscle. Caffeine produced no effect on maximal muscle force during voluntary or electrically stimulated 30 muscle actions. For submaximal effort, caffeine increased force output for low-frequency electrical stimulation before 20 and after muscle fatigue. Preexercise caffeine administration

Endurance time (min) Endurance 10 also increased by 17% repeated submaximum isometric muscular endurance.198 Caffeine exerts no ergogenic effect 0 13950 on anaerobic metabolic capacity (glycolysis) as measured during repeated high-intensity Wingate exercise tests.112 Caffeine (mg . kg BW–1) Page 582 of this chapter discusses caffeine’s lessening effect on the ergogenic benefits of creatine supplementation on Caffeine Placebo short-term muscular power. Figure 23.11 • Endurance performance (time to fatigue) following preexercise doses of caffeine in different con- Warning About Caffeine centrations. Cycling time (min) represents the average for nine male cyclists. All caffeine trials produced significantly better Individuals who normally avoid caffeine may experience performance than the placebo condition. No dose–response adverse effects when they consume it. Caffeine stimulates the relationship emerged between caffeine concentration and central nervous system and in quantities greater than 1.5 g per endurance performance. (From Pasman WJ, et al. The effect day can produce typical symptoms of caffeinism: restless- of different dosages of caffeine on endurance performance ness, headaches, insomnia, nervous irritability, muscle twitch- time. Int J Sports Med 1995;16:225.) ing, tremulousness, psychomotor agitation, and elevated heart rate and blood pressure; and it can trigger premature left- probably interact to produce caffeine’s facilitating effect on ventricular contractions. From the standpoint of temperature neuromuscular activity: regulation, caffeine acts as a diuretic, although with moderate 1. Lower threshold for motor unit recruitment caffeine consumption (Ͻ456 mg) it does not produce waterÐ 2. Alter excitationÐcontraction coupling electrolyte imbalances or reduced exercise heat tolerance.8 97818_ch23.qxd 8/4/09 4:47 PM Page 560

FOCUS ON RESEARCH Ergogenic Benefits of Caffeine

Costill DL, et al. Effects of caffeine ingestion on me- Costill tested its effects on muscle glycogen levels, the meta- tabolism and exercise performance. Med Sci Sports bolic mixture in exercise, and endurance performance in Exerc 1978;10:155. humans. Two female and seven male competitive cyclists (aver- á Ϫ1 Ϫ1 ➤ age VO ϭ 60 mL и kg и min ), consuming the same The potential ergogenic benefits of various substances and 2max á procedures have always interested sports competitors and ex- diet, performed a cycle ergometer VO2max test and two addi- ercise physiologists. Costill and colleagues tested the hypoth- tional endurance exercise trials separated by 3 days. In one esis that ingesting caffeine stimulated free fatty acid (FFA) trial, they consumed 200 mL of hot water containing5gof mobilization, retarded depletion of muscle glycogen, and decaffeinated coffee (D) 60 minutes before the exercise trial. The cycling test continued for as long as possible at a work consequently enhanced endurance exercise performance. á Previous research with animals and humans demonstrated intensity of 80% VO2max. In the second trial, subjects that elevating plasma FFA spared muscle glycogen and ex- consumed a hot drink containing5gofDplus 330 mg of tended exercise capacity. Because caffeine mobilizes FFA, caffeine (C) 60 minutes before the exercise test. Subjects remained unaware of the experiment’s purpose, with test order randomized for C and D trials. Blood samples, taken before and 0.28 during each trial, provided informa- 0.24 tion on plasma lactate, FFA, glycerol, 0.20 glucose, and triacylglycerols. In 0.16 addition, respiratory gas exchange 0.12 throughout exercise allowed compu- 0.08 tation of RQ and estimation of the G lycerol (mM) 0.04 nonprotein metabolic mixture. 0 The accompanying figure shows that total exercise time to ex- 0.6 haustion increased 19.5% during trial C (90.2 min) compared with trial D 0.5 (75.5 min). FFAs did not differ significantly between conditions (al-

0.4 though consistently higher in C trial), but the caffeinated drink produced

FFA (mM) FFA significantly higher plasma glycerol 0.3 levels and significantly lower RQ values. The RQ allowed the re- 0 searchers to estimate carbohydrate

1.0 oxidation during exercise (about 240 g in both trials). In contrast, fat oxidation with caffeine (118 g)

) exceeded oxidation without caffeine 2 (57 g). Subjects also perceived the 0.9

/ VO exercise as easier in the C condition. 2 This study demonstrated that C O consuming caffeine before exercise increased the lipolysis rate during RQ (V 0.8 sustained exercise. The effect of increased lipolysis could spare liver 0 and muscle glycogen early in exer- 0 102030405060 70 80 90 100 cise for later use. Subsequent re- Exercise time (min) search has confirmed caffeine’s ergogenic role in endurance exer- Decaffeinated trial Caffeine trial cise performance.

Average values for plasma glycerol, free fatty acid (FFA), and respiratory quotient (RQ) during endurance exercise after consuming either a caffeinated or decaffeinated liquid. Vertical bars (I) represent standard error of the mean. 97818_ch23.qxd 8/4/09 4:47 PM Page 561

CHAPTER 23 Special Aids to Exercise Training and Performances 561 Caffeine’s effect on fluid loss lessens when consumed during ginseng supplementation failed to affect performance or recov- exercise because (1) catecholamine release in exercise greatly ery from 30-second Wingate tests. Supplementation had no ef- reduces renal blood flow and (2) exercise enhances renal fect on mucosal immunity indicated by changes in secretory solute reabsorption and consequently water conservation IgA at rest or following intense exercise.84 When effectiveness (osmotic effect). has been demonstrated, the research failed to use adequate con- Although the effects of excess caffeine generally pose no trols, placebos, or double-blind testing protocols. health risk, a caffeine overdose can be lethal. The LD50 (lethal oral dose required to kill 50% of the population) for caffeine Ϫ Ephedrine is about 10 g (150 mg и kg body mass 1) for a 70-kg person. A 50-kg woman has an acute health risk with a caffeine intake Unlike ginseng, Western medicine recognizes the potent of 7.5 g. Moderate caffeine toxicity exists for small children amphetamine-like alkaloid compound ephedrine (with sym- who consume 35 mg per kg of body mass. Such observations pathomimetic physiologic effects) present in several species provide clear indication of the inverted U-shaped relationship of the plant ephedra (dried plant stem called ma huang [ma between certain exogenous chemicals and health and safety wong; Ephedra sinica]). The ephedra plant contains two (and probably exercise performance). Ingesting even small major active components, first isolated in 1928, ephedrine quantities of caffeine usually produces desirable effects— and pseudoephedrine. The medicinal role includes treatment consuming an excess can wreak havoc. of asthma, symptoms of the common cold, hypotension, and urinary incontinence, and as a central stimulant to treat de- Ginseng and Ephedrine pression. Physicians in the United States discontinued ephedrine as a decongestant and asthma treatment in the The popularity of herbal and botanical remedies to improve 1930s in favor of safer medications. The milder pseu- health, control body weight, and improve exercise perform- doephedrine remains common in nonprescription cold and flu ance has soared. Ginseng and ephedrine have been commonly medications and clinically treats mucosal congestion that ac- marketed as nutritional supplements to “reduce tension,” “re- companies hay fever, allergic rhinitis, sinusitis, and other res- vitalize,” “burn calories,” and “optimize mental and physical piratory conditions. This drug has been removed from the performance,” particularly during fatigue and stress. Ginseng banned substance list by the IOC and placed on the monitor- also plays a role as an alternative therapy to treat diabetes and ing program because of lack of evidence for an ergogenic ef- male impotence and stimulate immune function. fect. Labeling that indicates ephedra-containing compounds includes ephedra, ma huang, ephedrine, Ephedra sinica, sida cordifolia, epitonin, pseudoephedrine, and methyl ephedrine. Ginseng Ephedrine exerts central and peripheral effects, with the The ginseng root (Panax ginseng, C. A. Meyer), often latter reflected in increased heart rate, cardiac output, and sold as Panax or Chinese or Korean ginseng, serves no recog- blood pressure. Ephedrine produces bronchodilation in the nized medical use in the United States except as a soothing lungs owing to its ␤-adrenergic effect. High ephedrine agent in skin ointments. Commercial ginseng root prepara- dosages produce hypertension, insomnia, hyperthermia, and tions generally take the form of powder, liquid, tablets, or cardiac arrhythmias. Other side effects include dizziness, rest- capsules; widely marketed foods and beverages also contain lessness, anxiety, irritability, personality changes, gastroin- various types and amounts of ginsenosides. Dietary supple- testinal symptoms, and difficulty concentrating. ments need not meet the same quality control for purity and Despite the legal and scientific categorizations of potency as pharmaceuticals. Considerable variation exists in ephedrine as a potent drug, one could legally sell it as a di- the concentrations of marker compounds for ginseng, includ- etary supplement. Its claim for accelerated metabolism and ing potentially harmful levels of impurities and toxins such as enhanced exercise performance greatly increased ephedrine’s pesticides and heavy metals.116 popularity as a nutritional supplement. Many commercial Common claims for ginseng in the Western world are as weight-loss products have contained high-dosage combina- an energy booster, to diminish the negative effects of overall tions of ephedrine and caffeine designed to speed up metabo- stress, and to reduce the severity of cold symptoms. Little ob- lism, yet no credible evidence exists that any initial weight jective evidence exists to support the effectiveness of ginseng loss lasts beyond 6 months.235 as an ergogenic aid.159,276 For example, volunteers consumed The potent physiologic effects of ephedrine have led re- either 200 or 400 mg of the standardized ginseng concentrate searchers to investigate its potential as an ergogenic aid. No daily for 8 weeks in a double-blind research protocol.83 effect of a 40-mg dose of ephedrine occurred on indirect indi- Neither treatment affected submaximal or maximal exercise cators of exercise performance or ratings of perceived exer- performance, ratings of perceived exertion, or physiologic tion (RPE).70 The less concentrated pseudoephedrine also á parameters of heart rate, oxygen consumption, or blood lac- produced no effect on VO2max, RPE, aerobic cycling effi- tate concentrations. No ergogenic effects occurred for physio- ciency,122,253 anaerobic power output (Wingate test), time to logic and performance variables following a 1 week treatment exhaustion on a bicycle and a 40-km cycling trial,101 or phys- with a ginseng saponin extract administered in doses of either iologic and performance measures during 20 minutes of run- 181 á 50 8 or 16 mg per kg of body mass. Similarly, 8 weeks of ning at 70% of VO2max followed by a 5000-m time trial. 97818_ch23.qxd 8/4/09 4:47 PM Page 562

562 Section 4 Enhancement of Energy Transfer Capacity In contrast, a series of double-blind, placebo-controlled because the active muscle fibers rely predominantly on anaer- studies by the Canadian Defense and Civil Institute of obic energy transfer. Lactate accumulates with a concurrent Environmental Medicine using a preexercise ephedrine dosage fall in intracellular pH. Increased acidity ultimately inhibits (0.8 to 1.0 mg per kg body mass), either alone or combined energy transfer and contractile dynamics in the active muscle with caffeine, produced small but statistically significant ef- fibers, and exercise performance deteriorates. fects on endurance performance16,18,20 and anaerobic power The bicarbonate aspect of the body’s buffering system output during the early phase of the Wingate test.19 (see Chapter 14) provides a rapid first line of defense against Furthermore, an ergogenic effect of a relatively high dosage of intracellular increases in H+ concentration. Maintaining extra- pseudoephedrine (2.5 mg per kg body mass) was shown to en- cellular bicarbonate at a high level facilitates H+ efflux from hance runners’ times by 2.1% in a 1500-m time trial.123 the cell, which reduces intracellular acidosis. Increasing the Ephedrine supplementation also increased muscular endurance bicarbonate reserve before short-term anaerobic exercise during the first set of traditional resistance-training exercise.132 might enhance performance by delaying the fall in intracellu- Whether central mechanisms that increase arousal and toler- lar pH associated with exhaustive effort. Variations in preex- ance to discomfort, peripheral mechanisms that influence sub- ercise dosage of sodium bicarbonate and type of exercise to strate metabolism and muscle function, or the combined effect evaluate preexercise alkalosis have produced conflicting of both account for any ergogenic effect remains undetermined. results about the ergogenic effectiveness of buffering agents.108,124,231,249,268 To improve experimental design, one study investigated Not Without Risk the effects of acute metabolic alkalosis on exhaustive exercise Products containing ephedra represent less than 1% of that increased anaerobic metabolites. Six trained middle- sales of all herbal supplements, yet they account for 64% of distance runners ran an 880-m race under control conditions all reported adverse reactions. Consequently, ephedra poses a and following alkalosis induced by ingesting a sodium bicar- 200-fold greater risk than all other herbal supplements com- bonate solution (300 mg per kg body mass) or a calcium car- bined. Nearly 1400 adverse effects from ephedra use have bonate placebo of similar concentration. TABLE 23.7 shows that been reported to the FDA (www.fda.gov) from January 1993 the alkaline drink raised pH and standard bicarbonate level to February 2000. Incidents included 81 deaths, 32 heart at- before exercise. Subjects ran on average 2.9 seconds faster tacks, 62 cases of cardiac arrhythmia, 91 cases of increased under alkalosis and exhibited higher postexercise blood lac- blood pressure, 69 strokes, and 70 seizures. An evaluation of tate, pH, and extracellular H+ concentration than in the more than 16,000 adverse reactions showed “five deaths, five placebo condition. Augmented anaerobic energy transfer heart attacks, 11 cerebrovascular accidents, four seizures, and and/or delayed onset of intracellular acidification during in- eight psychiatric cases as ‘sentinel events’ associated with tense exercise most likely explains the ergogenic effect of prior consumption of ephedra or ephedrine.”235 In general, the preexercise alkalosis.26,204,211 Increased extracellular buffering cardiovascular toxic effects of ephedra (increased heart rate from preexercise sodium bicarbonate ingestion facilitates H+ ef- and blood vessel constriction) are not limited to massive flux from active muscle fibers during exercise in a dose depend- doses but rather to the amount recommended by the manufac- ent manner.75 This delays the fall in intracellular pH and its turer. In 2002, an Alabama jury awarded $4.1 million to four subsequent negative effects on muscle function. An improve- persons who suffered strokes or heart attacks after taking an ment of 2.9 seconds in 800-m race time represents a dramatic ephedra-based appetite suppressant produced by Metabolite performance improvement—a distance of 19 m at race pace International. In baseball spring training of 2003, ephedrine brings a last-place finisher to first place in most 800-m races! use was implicated in the death from organ failure complica- The ergogenic effect of preexercise alkalosis (use not tions in heat stroke of Baltimore Orioles pitcher Steve banned by WADA) also occurs for women (FIG. 23.12). Bechler. He allegedly used the ephedrine-containing supple- Physically active women performed one bout of maximal ment Xenadrine RFA-1 to facilitate weight loss. cycle ergometer exercise for 60 seconds on separate days Most sports organizations now ban ephedrine, and the under three conditions in a double-blind research design: (1) National Football League (NFL) was the first professional control, no treatment; (2) sodium bicarbonate dose of 300 mg sports league to do so. Professional baseball discourages и kg body massϪ1 in 400 mL of low-calorie flavored water 90 ephedrine use, but it does not ban it. Based on analysis of exist- minutes before testing; and (3) placebo of equimolar dose of ing data, the FDA banned ephedra on December 31, 2003, the sodium chloride (to maintain intravascular fluid status similar first time this federal agency banned a dietary supplement. In to bicarbonate condition) administered like the bicarbonate 2007, a petition for rehearing the ban in front of the tenth circuit treatment. Exercise capacity represented total work accom- of the U.S. Court of Appeals was denied by the U.S. Supreme plished in the 60-second ride. The figure’s inset box shows Court, upholding the FDA ban on sale of ephedra. that total work and peak power output reached higher levels with preexercise bicarbonate treatment than under either con- Buffering Solutions trol or placebo conditions. The bicarbonate treatment produced a higher blood lactate level in the immediate and Maximal exercise for 30 to 120 seconds dramatically alters 1-minute postexercise period; the effect explains the greater the chemical balance between intra- and extracellular fluids work capacity attained in the short-term, anaerobic exercise 97818_ch23.qxd 8/4/09 4:47 PM Page 563

CHAPTER 23 Special Aids to Exercise Training and Performances 563

TABLE 23.7 • Performance Time and Acid–Base Profiles for Subjects Under Control (Placebo) and Induced Preexercise Alkalosis Conditions Before and After an 800-M Race Variable Condition Pretreatment Preexercise Postexercise

pH Control 7.40 7.39 7.07 Placebo 7.39 7.40 7.09 Alkalosis 7.40 7.49a 7.18b Lactate Control 1.21 1.15 12.62 (mmol и LϪ1) Placebo 1.38 1.23 13.62 Alkalosis 1.29 1.31 14.29b Standard HCO3Ϫ1 Control 25.8 24.5 9.90 (mEq и LϪ1) Placebo 25.6 26.2 11.00 Alkalosis 25.2 33.5a 14.30b

Control Placebo Alkalosis

Performance time (min:s) 2:05.8 2:05.1 2:02.9c

From Wilkes D. et al. Effects of induced metabolic alkalosis on 800-m racing time. Med Sci Sports Exerc 1983;15:277. a Preexercise values significantly higher than pretreatment values. b Alkalosis values significantly higher than placebo and control values after exercise. c Alkalosis time significantly faster than control and placebo times.

Total work Peak power Trial (kJ) (W) Control 24.6 728.6 15 Placebo 24.5 727.2 ) Bicarbonate 26.9* 769.4* –1 L . * * 10

Blood lactate (mM 5

0 Pre Post 1 3 5 Time postexercise (min)

Control Placebo Bicarbonate

Figure 23.12 • Effects of bicarbonate loading on total work, peak power output, and postexercise blood lactate levels in moderately trained women. * Significantly higher than either control or placebo. (From McNaughton LR, et al. Effect of sodium bicarbonate ingestion on high intensity exercise in moderately trained women. J Strength Cond Res 1997;11:98.) 97818_ch23.qxd 8/4/09 4:47 PM Page 564

564 Section 4 Enhancement of Energy Transfer Capacity trial. Similar ergogenic benefits occur with exogenous the anterior pituitary gland to release adrenocorticotropic sodium citrate as the preexercise alkalinizing agent.120,171 hormone (ACTH), which induces the adrenal cortex to discharge the glucocorticoid hormone cortisol (hydrocortisone). Cortisol decreases amino acid transport into the cell; this Effect Related to Dosage and depresses anabolism and stimulates protein breakdown to its Degree of Anaerobiosis building-block amino acids in all cells except the liver. The Bicarbonate dosage and the cumulative anaerobic nature circulation delivers these “liberated” amino acids to the liver of exercise interact to influence the potential ergogenic effect for glucose synthesis (gluconeogenesis). Cortisol also serves of preexercise bicarbonate loading. Doses of at least 0.3 g per as an insulin antagonist by inhibiting cellular glucose uptake kg body mass facilitate H+ efflux from the cell and enhance a and oxidation. single 1- to 2-minute maximal effort and longer-term arm or A prolonged, elevated serum concentration of cortisol— leg exercise that exhausts within 6 to 8 minutes.168,174,218 No usually from therapeutic exogenous glucocorticoid intake in ergogenic effect emerges for performance typical of heavy- drug form—leads to excessive protein breakdown, tissue resistance training, perhaps because of the lower absolute wasting, and negative nitrogen balance. The potential cata- anaerobic metabolic load than in supramaximal whole-body bolic effect of cortisol has convinced many strength and running or cycling.202 Bicarbonate loading with all-out effort power athletes to use supplements thought to inhibit normal of less than 1 minute exerts an ergogenic effect with repetitive cortisol release. They believe that depressing cortisol’s nor- (intermittent) exercise.61 mal rise following exercise augments muscular development by attenuating catabolism. In this way, muscle tissue synthe- INTEGRATIVE QUESTION sis progresses unimpeded in recovery. Glutamine and phosphatidylserine are two supplements used to produce an Advise an Olympic-caliber weightlifter who plans anticortisol effect. to bicarbonate load because the competitive event requires all-out effort of an anaerobic nature. Glutamine Glutamine, a nonessential amino acid, is the most abundant amino acid in plasma and skeletal muscle. It accounts for High-Intensity Endurance Performance more than one-half of the muscles’ free amino acid pool. Glutamine exerts many regulatory functions, one of which pro- Preexercise-induced alkalosis does not benefit low- vides an anticatabolic effect that augments protein synthesis. intensity, aerobic exercise because pH and lactate remain at From a clinical perspective, glutamine supplementation effec- near-resting levels, but it may enhance aerobic exercise of tively counteracts the decline in protein synthesis and muscle higher intensity. Intense endurance exercise, while predomi- wasting from repeated glucocorticoid use.121 Infusing glutamine nantly aerobic, increases blood lactate and decreases pH, following exercise promotes muscle glycogen accumulation, which negatively affects performance. Eight trained male perhaps by serving as a gluconeogenic substrate in the liver.272 cyclists consumed sodium citrate (0.5 g per kg body mass) be- The potential anticatabolic and glycogen synthesizing 203 fore a 30-km time trial. Race times were faster and plasma effects of exogenous glutamine have promoted speculation pH and lactate concentrations higher after sodium citrate in- that supplementation might benefit resistance training effects. gestion than with the placebo. Despite the relatively small Daily glutamine supplementation (0.9 g per kg lean tissue anaerobic component in high-intensity aerobic exercise (com- mass) during 6 weeks of resistance training in healthy young pared with short-term, maximal exercise), ingesting a buffer adults did not affect muscle performance, body composition, before such exercise facilitates lactate and hydrogen ion or muscle protein degradation compared with a placebo.42 efflux and improves muscle function.172 Individuals who bicarbonate load often experience Glutamine and the Immune Response. Glutamine plays abdominal cramps and diarrhea about 1 hour after ingestion. an important role in normal immune function. One protective This adverse effect would surely minimize any potential er- aspect concerns glutamine’s use as metabolic fuel by infection- gogenic effect. Substituting sodium citrate (0.4 to 0.5 g per kg fighting cells, particularly lymphocytes and macrophages. body mass) for sodium bicarbonate reduces or eliminates ad- Glutamine plasma concentration decreases following pro- verse gastrointestinal effects while still providing ergogenic longed intense exercise, so glutamine deficiency has been 161,171 benefits. linked to immunosuppression from strenuous exercise (see Chapter 7).28,224 Anticortisol Compounds: Glutamine and Glutamine supplementation might lessen increased suscep- Phosphatidylserine tibility to upper respiratory tract infection (URTI) following prolonged competition or a bout of strenuous training. Marathoners The hypothalamus normally secretes corticotrophin-releasing who consumed a glutamine drink (5 g L-glutamine in 330 mL factor in response to emotional stress, trauma, infection, sur- mineral water) at the end of a race and then 2 hours later reported gery, and physical exertion. This releasing factor stimulates fewer URTI symptoms than unsupplemented athletes.45 More 97818_ch23.qxd 8/4/09 4:47 PM Page 565

CHAPTER 23 Special Aids to Exercise Training and Performances 565 specifically, 65% more athletes reported no symptoms of infec- dietary leucine catabolism. HMB supplements are taken be- tion than did a placebo group. The mechanism for gluta- cause of their potential nitrogen-retaining effects to prevent or mine’s effect on postexercise infection risk remains elusive. slow muscle damage and inhibit muscle breakdown (proteol- For example, subsequent studies by the same researchers ysis) with intense physical effort. showed no effect of glutamine supplementation on changes Research has studied the effects of exogenous HMB on in blood lymphocyte distribution.46 Dietary glutamine sup- skeletal muscle’s response to resistance training. In part 1 of plementation did not benefit lymphocyte metabolism or im- a 2-part study (FIG. 23.13), young adult men participated in mune function with more moderate exercise training in two randomized trials. In the first study, 41 subjects received rats.236 Research with humans indicates that preexercise 0, 1.5, or 3.0 g of HMB daily at two protein levels, either glutamine supplementation does not affect the immune re- 117 g or 175 g daily, for 3 weeks. The men resistance trained sponse following repeated bouts of intense exercise.213,284 during this time for 1.5 hours, 3 days a week. In the second Supplements of nine equal doses of 100 mg of L-glutamine study, 28 subjects consumed either 0 or 3.0 g of HMB daily per kg of body mass taken 30 minutes before the end of ex- and resistance trained for 2 to 3 hours, 6 days a week, for ercise, at the end of exercise, and 30-minutes into recovery 7 weeks. In the first study, HMB supplementation depressed abolished the postexercise decline in glutamine following a race but did not impact immune function.212

Phosphatidylserine 800 Phosphatidylserine (PS) is a glycerophospholipid typi- Control cal of a class of natural lipids that compose the structural 600 1.5g HMB components of the internal layer of the plasma membrane that surrounds all cells. Through its potential for modulating func- 3.0g HMB y strength (kg) 400 tional events in the plasma membrane (e.g., number and affinity of membrane receptor sites), PS might modify the neuroendocrine response to stress. In one study, healthy men 200 consumed 800 mg of PS derived from bovine cerebral cortex daily for 10 days.180 Three 6-minute intervals of cycle 0 ergometer exercise of increasing intensity induced physical –200 stress. Compared with the placebo condition, PS treatment di- Week 1 Week 3

minished ACTH and cortisol release without affecting growth Change in total bod A hormone release. These results confirmed that a single intravenous PS injection counteracted hypothalamic-pituitaryÐ 3.5 179 HMB + nutrient adrenal axis activation with exercise. A 750 mg per day powder supplement of PS for 10 days did not protect against delayed 2.5 onset muscle soreness or markers of muscle damage, inflammation, and oxidative stress following a bout of prolonged 1.5 downhill running.148 Soybean lecithin provides most PS for supplementation, yet research showing physiologic effects 0.5 has used bovine-derived PS. Subtle differences in the chemical structure of these two forms of PS may create differences –0.5 Placebo in physiologic action, including the potential for ergogenic effects.

Fat-free bod y mass gain (kg) Fat-free –1.5 0210 0304050 B Day of study ␤-Hydroxy–␤-methylbutyrate ␤-HydroxyÐ␤-methylbutyrate (HMB), a bioactive metabo- Figure 23.13 • A. Change in muscle strength (total weight lite generated in the breakdown of the essential branched- lifted in upper- and lower-body exercises) during study 1 chain amino acid leucine, decreases protein loss during stress (week 1 to week 3) in subjects who supplemented with HMB. by inhibiting protein catabolism. In rats and chicks, less pro- Each group of bars represents one complete set of upper- and tein breakdown and slight increase in protein synthesis oc- lower-body workouts. B. Total body electrical conductivity- assessed change in FFM during study 2 for a control group curred in muscle tissue (in vitro) exposed to HMB.151 An that received a carbohydrate drink (placebo) and a group that HMB-induced increase occurred in fatty acid oxidation in 49 received 3 g of Ca-HMB each day mixed in a nutrient powder mammalian muscle cells exposed to HMB. Depending on (HMB + nutrient powder). (From Nissen S, et al. Effect of the quantity of HMB in food (relatively rich sources include leucine metabolite ␤-hydroxy–␤-methylbutyrate on muscle catfish, grapefruit, and breast milk), humans synthesize be- metabolism during resistance-exercise training. J Appl Physiol tween 0.3 and 1.0 g of HMB daily, with about 5% from 1996;81:2095.) 97818_ch23.qxd 8/4/09 4:47 PM Page 566

566 Section 4 Enhancement of Energy Transfer Capacity the exercise-induced rise in muscle proteolysis (reflected by NONPHARMACOLOGIC APPROACHES urinary 3-methylhistidine and plasma creatine phosphokinase [CPK] levels) during the first 2 weeks of exercise training. Athletes often use physical, mechanical, physiologic, and nu- These biochemical indices of muscle damage were 20 to 60% tritional means to potentiate ergogenic effects. lower in the HMB-supplemented group. In addition, the supplemented group lifted more total weight during each training week (Figure. 23.13A), with the greatest effect in the group Red Blood Cell Reinfusion—Blood Doping receiving the largest HMB supplement. Muscular strength in- Red blood cell reinfusion, often called induced erythro- creased 8% in the unsupplemented group and more in the cythemia, blood boosting, or blood doping, gained public HMB-supplemented groups (13% for the 1.5-g group and prominence as a possible ergogenic technique during the 18.4% for the 3.0-g group). Added protein (not indicated in 1972 Munich Olympics, when a relatively unknown Finnish graph) did not affect any of the measurements; one should runner allegedly used this procedure prior to his two gold view this lack of effect in proper context—the “lower” pro- medalÐwinning 5000- and 10,000-m runs. tein quantity (115 g и dϪ1) equaled twice the RDA. In the second study, individuals who received HMB sup- How It Works plementation had higher FFM than the unsupplemented group at 2 and 4 to 6 weeks of training (Fig. 23.13B). However, at Red blood cell reinfusion involves withdrawing 1 to the last measurement during training, the difference between 4 units (1 unit ϭ 450 mL of whole blood) of a person’s blood, groups decreased and failed to differ from the difference be- immediately reinfusing the plasma, and placing the packed tween pretraining baseline values. red cells in frozen storage for later infusion (autologous The mechanism for any HMB effect on muscle metabo- transfusion). Homologous transfusion infuses a type- lism, strength improvement, and body composition remains matched donor’s blood. To prevent dramatic reductions in unknown. Perhaps this metabolite inhibits normal proteolytic blood-cell concentration, each unit of blood withdrawal takes processes that accompany intense muscular overload. place at 3- to 8-week intervals because it takes this time to Although the results demonstrate an ergogenic effect for reestablish normal red blood cell levels. Stored blood cells are HMB supplementation, it remains unclear just what compo- then infused 1 to 7 days before an endurance event; this nent of the FFM (protein, bone, water) HMB affects. increases red blood cell count and hemoglobin levels from Furthermore, the data in Figure 23.13B indicate potentially 8 to 20%. transient body composition benefits of supplementation that Hemoconcentration translates to an average hemoglobin tend to revert toward the unsupplemented state as training increase for men from a normal 15 g per dL of blood to 19 g progresses. per dL (hematocrit increases 40 to 60%). Hematologic param- Not all research shows beneficial effects of HMB sup- eters remain elevated for at least 14 days. Theoretically, the plementation with resistance training.207 One study evaluated added blood volume contributes to a larger maximal cardiac the effects of variations in HMB supplementation (approxi- output, while red blood cell packing increases the blood’s mately 3 vs. 6 g и dϪ1) on muscular strength during 8 weeks oxygen-carrying capacity. Enhanced oxygen transport and de- of whole-body resistance training in untrained young adult livery to active tissues provides meaningful performance ben- men.97 The study’s primary finding indicated that HMB sup- efits to endurance athletes. plementation, regardless of dosage, produced no difference An ergogenic effect occurs with infusion of 900 to in most of the strength data (including 1-RM strength) com- 1800 mL of freeze-preserved autologous blood. Each pared with the placebo group. In contrast to the findings pre- 500-mL infusion of whole blood (equivalent to 275 mL of sented in Figure 23.13A, increases in training volume packed red cells) adds about 100 mL of oxygen to the remained similar among groups. In both HMB-supplemented blood’s total oxygen-carrying capacity—each 100 mL of groups, lower CPK levels in recovery indicated some poten- whole blood carries about 20 mL of oxygen. An elite en- tial effect of HMB to inhibit muscle breakdown. The group durance athlete’s total blood volume circulates 5 to 6 times that consumed the lower HMB dosage increased more in each minute in intense exercise, so the potential “extra” oxy- FFM than the other two groups. Inferences from these find- gen available to the tissues from red cell reinfusion averages ings are limited because skinfolds assessed body composi- 500 mL (0.5 L). tion changes. HMB supplementation with a daily dosage as Blood doping might also produce effects opposite to high as 6 g и dϪ1 during 8 weeks of resistance training does those intended. For example, a large red blood cell infusion not adversely affect hepatic enzyme function, blood lipid (and increase in blood cell concentration) could increase profile, renal function, or immune function.98 Additional blood viscosity, or “thickness,” and thus decrease cardiac out- studies must assess the long-term effects of HMB supple- put, blood flow velocity, and peripheral oxygen supply-effects ments on body composition, training response, and overall that reduce aerobic capacity and endurance performance. Any health and safety. Age does not affect responsiveness to increase in blood viscosity could also compromise blood flow HMB supplementation.280 through narrowed, atherosclerotic vessels of individuals with artery disease to increase their risk for heart attack or stroke. 97818_ch23.qxd 8/4/09 4:47 PM Page 567

CHAPTER 23 Special Aids to Exercise Training and Performances 567 Does It Work?

A theoretical basis for blood doping exists and experi- +12 mental evidence justifies its use for physiologic reasons.230 +8 Much of the early conflict concerning ergogenic benefits came from poor experimental design, inconsistent criteria for +4 exercise performance, diverse blood storage techniques, and 0 Control value variations in timing and quantity of blood withdrawn and re- control value –4 placed. Early research in this area noted a rapid increase in Packed RBC 78 –8 VúO2max following infusion of whole blood. One study reported a 23% overnight increase in exercise performance and –12

Percent o f Percent 02 460246 8 10 12 14 16 ú 81 Red blood concentration: a 9% increase in VO2max with blood doping. Subsequent in- Removal Reinfusion vestigations (including a study by a past critic of the technique) Weeks support previous findings and show physiologic and performance improvements with red blood cell reinfusion.217,242 Figure 23.14 • Time course of hematologic changes after Differences in results among various studies of exercise removal and reinfusion of 900 mL of freeze-preserved blood. performance following red blood cell reinfusion largely result (From Gledhill N. Blood doping and related issues: a brief from variations in blood storage methods. Freezing red blood review. Med Sci Sports Exerc 1982;14:183.) cells permits storage for more than 6 weeks without significant loss of cells. With storage at 4¡C (used in some earlier studies), substantial hemolysis occurs after only 3 weeks. A New Twist: Hormonal Blood Boosting This represents an important difference because it usually takes a person 5 to 6 weeks to reestablish blood cells lost after Endurance athletes now use epoetin, a synthetic form of ery- withdrawal of two units of whole blood (FIG. 23.14). thropoietin (EPO), to eliminate the cumbersome and lengthy With appropriate blood storage methods, red blood cell blood doping process, This hormone, produced by the kidneys, reinfusion elevates hematologic parameters of men and regulates red blood cell production within the marrow of the women. This in turn translates to a 5 to 13% increase in aero- long bones, but also is essential in the synthesis and proper bic capacity, decreased heart rate and blood lactate during functioning of several erythrocyte membrane proteins, particu- submaximal exercise, and augmented endurance at sea level larly those facilitating lactate exchange.9,33,59 Medically, and altitude. In addition, thermoregulatory benefits during ex- exogenous recombinant human EPO, commercially available ercise in the heat (reduced body heat storage and improved since 1988, has proved useful in combating anemia in patients sweating response) result from red blood cell reinfusion. undergoing chemotherapy or with severe renal disease. Increased oxygen content in arterial blood in the infused state Normally, a decrease in red blood cell concentration or decline likely “frees” blood for delivery to the skin for heat dissipa- in the pressure of oxygen in arterial blood—as in severe pul- tion during exercise heat stress while adequately supplying monary disease or on ascent to high altitude—releases this active tissues. TABLE 23.8 illustrates hematologic, physiologic, hormone to stimulate erythrocyte production. The 12% in- and performance responses for five adult men during submax- crease in hemoglobin and hematocrit that typically follows a imal and maximal exercise before and 24 hours after infusion 6-week EPO treatment greatly improves endurance exercise of 750 mL of packed red blood cells. These response patterns performance.80,227 Unfortunately, self-administration in an generally represent the current thinking in this area. unregulated and unmonitored manner—simply injecting the

TABLE 23.8 • Physiologic, Performance, and Hematologic Characteristics Before and 24 Hours After Reinfusion of 750 ml of Packed Red Blood Cells Variable Preinfusion Postinfusion Difference Difference, %

Hemoglobin, g и dL bloodϪ1 13.8 17.6 3.8b ϩ27.5b Hematocrita, % 43.3 54.8 11.5b ϩ26.5b á и Ϫ1 Ϫ Ϫ Submaximal VO2, L min 1.60 1.59 0.01 0.6 Submaximal HR, b и minϪ1 127.4 109.2 18.2b Ϫ14.3b á и Ϫ1 b ϩ b VO2max, L min 3.28 3.70 0.42 12.8 и Ϫ1 Ϫ Ϫ HRmax, b min 181.6 180.0 1.6 0.9 Treadmill run time, s 793 918 125b 15.8b

From Roberston RJ, et al. Effect of induced erythrocythemia on hypoxia tolerance during exercise. J Appl Physiol 1982;53:490. aHematocrit expressed as the percentage (%) of 100 mL (1 dL) of whole blood occupied by red blood cells. bDifference statistically significant. 97818_ch23.qxd 8/4/09 4:47 PM Page 568

568 Section 4 Enhancement of Energy Transfer Capacity hormone requires much less sophistication than blood doping wisdom maintains that preliminary exercise helps the procedures—can increase hematocrit more than 60%. This performer prepare physiologically or psychologically and re- dangerously high hemoconcentration (and corresponding induces the likelihood of joint and muscle injury. With animals, crease in blood viscosity) increases the likelihood for stroke, injuring a “warmed-up” muscle requires more force and heart attack, heart failure, and pulmonary edema. greater muscle length than injuring a muscle in the “cold” EPO use has become particularly prevalent in cycling condition.229 The warming-up process stretches the muscle- competition and allegedly contributed to at least 18 deaths tendon unit to allow greater length and less tension on expo- (mainly from heart attack) among competitive cyclists. sure to a given external load. Because EPO cannot be detected in urine, the blood hemat- Warm-up generally fits into one of two categories ocrit serves as a surrogate marker. The International Cycling (although overlap exists): Union has set a hematocrit threshold of 50% for males and 1. General warm-up uses body movements or 47% for females; the International Skiing Federation uses a Ϫ “loosening-up” exercises unrelated to the specific hemoglobin concentration of 18.5 g и dL 1 as the threshold neuromuscular actions of the anticipated for disqualification. Hematocrit cutoff values of 52% for performance. Examples include calisthenics and men and 48% for women (roughly 3 standard deviations stretching. above the mean) represent “abnormally high” or extreme 2. Specific warm-up applies big-muscle, rhythmic values in triathletes.188 Use of hematocrit level cutoff raises movements that provide skill rehearsal in the activ- the unanswered question of the number of disqualified ity. Examples include swinging a golf club, throwing “clean” cyclists. Estimates place this number between 3 and a baseball or football, tennis practice, basketball 5% because of factors that affect normal variation in hemat- shooting and movements, and preliminary lead-up in ocrit such as genetics, posture, altitude training, and hydra- the high jump or pole vault. tion level. Current concern centers on an anomaly in iron metabo- Psychologic Considerations lism frequently observed among high-level international cyclists. Many of these athletes show serum iron levels above Competitors at all levels generally believe that perform- 500 ng и LϪ1 (normal: 100 ng и LϪ1), with some values as high ing some prior skill-related activity prepares them mentally to as 1000 ng и LϪ1. The elevated iron level results from their focus on the upcoming performance. A specific warm-up re- regular injections of supplemental iron to support increased lated to the intended activity also may improve the necessary synthesis of red blood cells induced by repeated EPO use. skill and coordination requirements. Consequently, sports that Chronic iron overload increases the risk of liver dysfunction require accuracy, timing, and precise movements generally among these athletes. benefit from some type of specific or “formal” preliminary The enhancement of oxygen availability to muscles by practice. EPO analog and mimetics constitutes one of the main chal- The notion also exists that prior exercise before strenuous lenges to doping control. The concern of sports governing effort gradually prepares a person to go “all out” without fear bodies has now shifted from simple red blood cell reinfusion of injury. The ritual warm-up of baseball pitchers exemplifies to concern about transfection to an athlete’s genes that code this belief. Is it conceivable that a pitcher would enter a game, for erythropoietin and its subsequent impact on exercise throwing at competitive speeds, without previously warming performance.193 Sports authorities have incorporated such up? Would any athlete begin competition without first stretch- “gene doping” among the prohibited practices. ing and engaging in a particular form, intensity, or duration of warm-up? Most performers would respond with a definite no, Other Means to Enhance Oxygen Transport yet objective support for this response remains elusive. One reason is the difficulty designing a well-controlled experiment New classes of substances may emerge to enhance aer- with topflight athletes to determine the necessity of warming obic exercise performance. These doping threats include up and whether it improves subsequent performance with re- perfluorocarbon emulsions and solutions formulated from duced injury risk. For preexercise stretching, research with either bovine or human hemoglobin that improve oxygen army recruits indicates that a typical muscle-stretching proto- transport and delivery to muscle. Despite their potential col in the preexercise warm-up produces no clinically mean- benefits in clinical use, these substances exhibit potentially ingful reductions in risk of exercise-related injury compared lethal side effects that include increased systemic and pul- with subsequent exercise without warm-up.201 In addition, monary blood pressure, renal toxicity, and impaired immune strength loss, loss of motion, soreness, or markers of muscle function. damage from eccentric exercise were no different between groups that received preexercise passive warm-up with short- Warm-Up (Preliminary Exercise) wave diathermy, active warm-up with concentric muscle actions, or no warm-up.86 Coaches, trainers, and athletes at all levels of competition Certain sport-related situations require peak perform- generally recommend engaging in some type of physical ac- ance with little time for warming up. A reserve player enter- tivity or warm-up prior to vigorous exercise. Conventional ing the last few minutes of a game has no time for stretching, 97818_ch23.qxd 8/4/09 4:47 PM Page 569

CHAPTER 23 Special Aids to Exercise Training and Performances 569 vigorous calisthenics, or taking practice shots; the player Clinical Considerations: Warm-Up Prior to must go all out and achieve optimal performance without Sudden Strenuous Exercise warm-up except that done before the game or at intermission. Do more injuries occur in such cases? Does physical perform- Sudden exertion can trigger the onset of myocardial infarction, particularly in sedentary persons and those with la- ance (e.g., shooting, rebounding, or basketball defense) dete- 35,177 riorate during the first few minutes of this “unwarmed” tent coronary artery disease. With this in mind, condition from that proceeded by a warm-up? Future research consideration of possible benefits from warming up takes on must address such questions. clinical significance. Several studies have evaluated the Psychologic factors, including an athlete’s ingrained be- effects of preliminary exercise on the cardiovascular response lief in the importance of warming up, establish a definite bias to sudden, strenuous exercise. The findings provide an essen- when comparing maximum performance with and without tially different physiologic framework to justify warm-up that warm-up. It is difficult if not impossible to obtain a maximum relates importantly to adult fitness and cardiac rehabilitation effort without warm-up if a subject believes in the importance programs and occupations and sports that require sudden of preliminary exercise. bursts of physical effort. In one study, 44 men free of overt symptoms of coronary artery disease ran on a treadmill at high intensity for 10 to 13 Physiologic and Performance Effects 15 seconds without prior warm-up. Evaluation of postexercise ECGs revealed that 70% of the subjects displayed abnor- One study evaluated the effect of warm-up on 2-minute mal changes attributable to inadequate myocardial oxygen sprint-cycling performance at 120% of the power output at supply unrelated to age or fitness level. To evaluate the effect ú VO2max. Warm-up produces a higher muscle temperature, in- of a warm-up, 22 of the men with an abnormal ECG from the creased local muscle oxygen availability and oxygen uptake, treadmill run jogged in place at moderate intensity (heart rate, lower blood lactate level, and higher oxygen consumption 145 b и minϪ1) for 2 minutes before treadmill running. With during the early phase of exercise than the no-warm-up con- this warm-up, 10 men now showed normal tracings during 69,216 dition. Warm-up exercise performed at moderate- and sudden exertion, while another 10 men displayed improved high-intensity improved intense cycling performance by 2 to ECG responses; only two subjects showed significant abnor- 39 3%. Also, a pre-exercise warm-up irrespective of intensity malities. In a subsequent study, the exercise blood pressure enhanced a 3 to 4 minute (3-km) cycling time trial time. response also improved with prior warm-up.14 For seven men This effect likely resulted from an acceleration of oxygen with no warm-up, systolic blood pressure averaged 168 mm uptake kinetics from augmented blood flow at the onset of Hg immediately after the 15-second treadmill run. This 113 exercise. An active warm-up 5 minutes prior to a 30-sec- decreased to 140 mm Hg when the 2-minute jog-in-place ond maximal sprint on a bicycle ergometer produced less warm-up preceded exercise. blood and muscle lactate than equivalent effort without a Coronary blood flow does not adjust instantaneously to a 109 physical warm-up. Differences in muscle temperature sudden increase in myocardial work; transient myocardial with an active warm-up could not account for the ergogenic ischemia (poor oxygen supply) can occur in apparently effect because exercise in the control condition also in- healthy and fit individuals. Prior warm-up (at least 2 min of volved passively heating the muscle to the same tempera- easy jogging) benefits the subsequent ECG and blood pres- ture. These findings suggest a decreased reliance on sure responses to vigorous exercise to indicate a more favor- anaerobic sources of energy during the exercise period pre- able relationship between myocardial oxygen supply and ceded by a physical warm-up. demand. Warming up before strenuous exercise is particularly Five mechanisms explain why warm-up “should” im- important for individuals with limited myocardial blood flow prove physical performance and exercise capacity because of from coronary artery disease. A brief warm-up provides more subsequent increases in blood flow and muscle and core tem- optimal blood pressure and hormonal adjustments at the onset perature: of subsequent strenuous exercise. The warm-up serves two 1. Faster muscle contraction and relaxation beneficial purposes under these conditions: 2. Greater economy of movement from lowered viscous 1. Reduces myocardial workload and thus the myocar- resistance within active muscles dial oxygen requirement 3. Facilitated oxygen delivery and use by muscles be- 2. Augments blood flow through the coronary arteries cause hemoglobin releases oxygen more readily at higher temperatures (Bohr effect) 4. Facilitated nerve transmission and muscle metabo- Oxygen Inhalation (Hyperoxia) lism because increased temperature accelerates bod- Athletes breathe oxygen-enriched or hyperoxic gas mixtures ily processes; a specific warm-up may also facilitate during time-outs, at half-time, or following strenuous exer- recruitment of required motor units cise. They believe this procedure enhances the blood’s 5. Increased blood flow through active tissues as the oxygen-carrying capacity to facilitate oxygen transport to ac- local vascular bed dilates from increased metabolism tive or recovering muscles. The fact remains that when and higher muscle temperature healthy persons breathe ambient air at sea level, hemoglobin 97818_ch23.qxd 8/4/09 4:47 PM Page 570

570 Section 4 Enhancement of Energy Transfer Capacity in blood leaving the lungs normally remains 95 to 98% satu- The athlete who breathes an oxygen-rich mixture on the rated with oxygen (see Chapter 13). In physiologic terms, sideline before returning to the competition does not gain a consider these two factors: competitive edge from physiologic benefits. This is particularly ironic in football, because metabolic reactions that do 1. Breathing air with a higher than normal oxygen con- not require oxygen generate almost all of the energy to power centration increases oxygen transport by hemoglobin each play. to only a small extent—by about 1 mL of extra oxygen for every deciliter of blood (10 mL O2 per liter). 2. Oxygen that dissolves in plasma when breathing a hy- Oxygen Breathing During Exercise peroxic mixture also increases by about 0.4 mL per deciliter of blood (4.0 mL O2 per liter), or from the Breathing hyperoxic gas during submaximal and maxi- normal 0.3 mL per deciliter (3.0 mL per liter) to about mal aerobic exercise enhances endurance performance. 0.7 mL per deciliter (7.0 mL per liter) of blood. Oxygen breathing during vigorous exercise accelerates oxygen consumption at the onset of exercise (smaller oxy- Based on these two factors, the blood’s oxygen-carrying gen deficit in repeated bouts of intense effort); reduces capacity under hyperoxic conditions potentially increases by blood lactate, heart rate, and pulmonary ventilation in sub- only about 14 mL of oxygen for every liter of blood—10 mL maximal exercise; and increases Vú O and the exercise “extra” attached to hemoglobin and 4 mL “extra” dissolved in 2max training intensity.166,194,214 In one study, subjects performed plasma. a 6.5-minute endurance ride on a bicycle ergometer at an ex- ú ercise level equal to 115% of VO2max while breathing either room air or 100% oxygen.286 Tanks of compressed gas sup- Preexercise Oxygen Breathing plied both air and oxygen to mask a subject’s knowledge of Blood volume for a 70-kg person averages about 5000 the breathing mixture. FIGURE 23.15A shows superior en- mL (5.0 L). Breathing hyperoxic gas adds about 70 mL of durance (less drop-off in pedal revolutions) while breathing oxygen to the total blood volume (5.0 L of blood ϫ 14 mL oxygen during exercise. FIGURE 23.15B shows that the hyper- “extra” O2 per liter of blood). Despite any potential psycho- oxic condition produced higher oxygen consumptions logic benefit for the athlete who believes that preexercise throughout exercise. oxygen breathing helps subsequent performance, this proce- FIGURE 23.16 shows that oxygen consumption of the dure confers only a trivial physiologic advantage from any quadriceps muscle of seven trained subjects during maximum additional oxygen per se. This small benefit emerges only if knee-extension exercise varied with the level of inspired oxy- subsequent exercise takes place without breathing ambient air gen, averaging lower in hypoxia (12% O2) than in normoxia in the interval between hyperoxic breathing and exercise. This (21% O2) and higher in hyperoxia (100% O2) than normoxia. occurs because ambient air’s lower oxygen pressure causes The figure also includes confirmatory results (dotted yellow any additional oxygen in the blood to exit the body. line) from a previous study of cycle ergometry under

60 5.0

–1 56 4.0 ) –1 min . 52 3.0 min . Pedal 48 (L 2.0 2

44 VO 1.0 revolutions

A 02123456 B 01 3456 Exercise duration (min) Exercise duration (min)

100% O2 Room air

Figure 23.15 • A. Endurance (measured by pedal revolutions each minute) while breathing 100% oxygen or ambient air. B. Oxygen consumption curves during the endurance rides show enhanced oxygen consumption while breathing oxygen. (Data from Weltman A, et al. Effects of increasing oxygen availability on bicycle ergometer endurance performance. Ergonomics 1978;21:427.) 97818_ch23.qxd 8/4/09 4:47 PM Page 571

CHAPTER 23 Special Aids to Exercise Training and Performances 571 exercising at a 20- to 30-L cardiac output. If the muscles me- ú tabolized the added oxygen during exercise, VO2max would 80 increase by 5 to 10%. The increased partial pressure of oxygen in solution from breathing hyperoxic gas also facilitates 70 its diffusion across the tissueÐcapillary membrane into the

) 60 mitochondria. More rapid oxygen diffusion may account for

–1 the higher oxygen consumption early in exercise under hyper- 2peak 100 50 oxic conditions. Reduced pulmonary ventilation under hyper- 21 100g oxic conditions lowers the oxygen cost of breathing. .

40 Theoretically, this liberates oxygen for use by the active, non- –1 12 ventilatory skeletal muscles. Hyperoxia also increases sus-

min 30 100 tained muscle performance in intense static and dynamic . Inspired O 21 2 (%) movements not affected by central circulatory factors. The 20 (mL (mL 12 high oxygen pressure in blood and fluids within the active Skeletal muscle VO muscle environment may explain this ergogenic effect. 10 Breathing hyperoxic mixtures offers positive ergogenic benefits during endurance exercise, but offers limited practi- 0 0 20 40 60 80 cal sports application. The “legality” of using an appropriate Oxygen delivery (mL . min–1 . 100g–1) breathing system during actual competition seems unlikely.

Cycle exercise Knee-extensor exercise Oxygen Breathing During Recovery

Figure 23.16 • Relationship between skeletal muscle V˙O2peak Breathing hyperoxic mixtures does not facilitate recov- and oxygen delivery per 100 g of muscle during conventional ery from exercise or improve performance in a subsequent maximal cycle ergometry exercise (yellow) and knee- exercise bout. FIGURE 23.17 illustrates the effects of breathing extension exercise (purple) under hypoxia, normoxia, and hyperoxic gas in recovery from strenuous exercise on subse- hyperoxia. (From Richardson RS, et al. Evidence of O2 quent exercise performance. Following 1 minute of all-out supply–dependent V˙O in exercise-trained human 2max bicycle ergometer exercise, subjects recovered while breath- quadriceps. J Appl Physiol 1999;86:1048.) ing either room air or 100% oxygen for 10 or 20 minutes. They then repeated the all-out bicycle ride. No significant differences emerged in cumulative revolutions (graph A) and 150 comparable conditions. Cycle ergometry produced lower 6-second-by-6-second revolutions (graph B) for the 1-minute ú muscle-specific VO2peak values than knee-extension exercise. ride after breathing room air or 100% oxygen during recovery However, the slopes of the lines relating oxygen delivery to from previous exercise. Also, breathing either room air or peak muscle oxidative metabolism were remarkably similar oxygen yielded similar blood lactate levels in the 10- or for both exercise modes. For maximal knee-extension exer- 20-minute recovery periods. This indicated that breathing oxy- cise, oxygen content of venous blood leaving the active mus- gen in recovery did not facilitate lactate removal. Subsequent cles remained essentially equal among conditions averaging research supports these findings; breathing oxygen after short и Ϫ1 4mL dL . Oxygen delivery in arterial blood increased intervals of submaximal and maximal exercise did not affect и Ϫ1 from 17.3 to 19.5 to 21.8 mL dL with increasing levels of recovery kinetics for minute ventilation, heart rate, or serum oxygen inhalation. Consequently, the hyperoxic condition lactate or the level of ensuing exercise performance.215,289 during maximal exercise produced the largest skeletal muscle ú a-vO2 difference and VO2peak. Similarly, maximal exercise intensity decreased 25% when breathing 12% inspired oxygen Modification of Carbohydrate Intake and increased 14% under 100% inspired oxygen compared with normoxic conditions. Oxygen delivery to active muscles Increased carbohydrate intake before and during intense aero- in the circulation, not use via mitochondrial metabolism, limbic exercise, including periods of strenuous training, is a sound its aerobic exercise. macronutrient manipulation that benefits exercise performance, Breathing hyperoxic gas does not increase maximal car- lowers ratings of perceived exertion, and improves psychologic 1,262 diac output; thus, an expanded a-vøO2 difference must account state. Vigilance and mood also improve with a carbohy- for the increased exercise oxygen consumption. The small drate beverage administered during a day of sustained aerobic increases in arterial hemoglobin saturation and dissolved activity interspersed with rest periods.160 One of the more pop- plasma oxygen with hyperoxic breathing increase total oxy- ular nutritional exercise modifications used by endurance ath- gen availability as blood volume circulates 4 to 7 times each letes to augment glycogen reserves involves carbohydrate minute in strenuous exercise. The additional but relatively loading, or glycogen supercompensation. The procedure pro- small 14 mL of oxygen in each 1 L of blood from breathing duces considerably higher “packing” of muscle glycogen than hyperoxic gas represents considerable extra oxygen when simply maintaining a high-carbohydrate diet. Normally, each 97818_ch23.qxd 8/4/09 4:47 PM Page 572

572 Section 4 Enhancement of Energy Transfer Capacity

14 13 120 12

100 11 10 80 9 8 60 7 40 6 6-s by revolutions

C umlative revolutions 5 20 4

A 0 12 24 36 48 60 B 066 12 18 24 30 36 42 48 54 0 Exercise duration (s) Exercise duration (s)

100% O2 Room air

Figure 23.17 • Cumulative (A) and absolute (B) 6-second pedal revolutions on a bicycle ergometer during 1 minute of maximal exercise after breathing either 100% oxygen or ambient air during recovery from a previous maximal exercise bout. (From Weltman A, et al. Exercise recovery, lactate removal, and subsequent high-intensity exercise performance. Res Q 1977;48:786.)

100 g of muscle contains about 1.7 g of glycogen; carbohydrate fed a high-carbohydrate diet was triple that when the same loading packs up to 4 to 5 g of glycogen. subjects consumed a high-fat diet of similar energy content (see Fig. 1.9).23 Carbohydrate represents the important energy substrate during 1 to 2 hours of high-intensity exercise, so re- Nutrient-Related Fatigue searchers searched for additional ways to increase preexercise in Prolonged Exercise glycogen reserves. Glycogen stored in the liver and active muscle supplies most of the energy for intense aerobic exercise. Prolonging Classic Loading Procedure such exercise reduces the body’s glycogen reserves. This allows fat catabolism—from adipose tissue and liver fatty acid TABLE 23.9 presents the classic procedure for achieving the mobilization and intramuscular fat stores—to supply a pro- supercompensation effect. The first phase involves reducing the gressively greater percentage of energy. A substantially low- muscle’s glycogen content with prolonged exercise about ered muscle glycogen level precipitates fatigue, although 6 days before competition. Glycogen supercompensation oc- active muscle maintains sufficient oxygen with an almost un- curs only in the specific muscles depleted by exercise, so ath- limited potential energy from fat. Consuming a glucose and letes must engage the muscles activated in their sport. Preparing water solution near the point of fatigue allows exercise to for marathon running, endurance swimming, or bicycling re- continue, but for all practical purposes, “the muscles’ fuel quires 90 minutes of moderately intense submaximal exercise tank reads empty.” Reliance on fat catabolism decreases in the specific activity. The athlete then maintains a low-carbo- power output from the considerably slower mobilization and hydrate diet (about 60 to 100 g и dϪ1) for several days to further breakdown of fat than carbohydrate. Marathon runners use deplete glycogen stores. (Note: Glycogen depletion increases in- the term hitting the wall (endurance cyclists use bonking) to termediate forms of the glycogen-storing enzyme glycogen syn- describe sensations of fatigue and muscle pain associated thase within the depleted muscle fibers.) Moderate training when exercising with severe glycogen depletion. continues during this time. Then, 3 days before competing, the In the late 1930s, Nordic scientists reported enhanced athlete switches to a high-carbohydrate diet (400 to 700 g и dϪ1) endurance performance when athletes consumed carbohydrate- and maintains this intake up to the precompetition meal. The rich diets. Conversely, switching to high-fat diets drastically re- supercompensation diet should also contain adequate daily duced endurance capacity. Modifying the diet’s macronutrient protein, minerals and vitamins, and abundant water. Super- composition alters carbohydrate stores and profoundly affects compensated muscle glycogen levels remain stable for at least subsequent prolonged high-intensity exercise performance. In 3 days during a maintenance phase (in a nonexercising individ- a classic series of experiments, endurance capacity for subjects ual) if the diet contains 60% of calories as carbohydrate.103 97818_ch23.qxd 8/4/09 4:47 PM Page 573

CHAPTER 23 Special Aids to Exercise Training and Performances 573 diet—but maintain the low-carbohydrate diet for only 1 day. TABLE 23.9 • Two-Stage Dietary Plan to With no adverse effects, the low-carbohydrate diet can gradu- Increase Muscle Glycogen ally extend to a maximum of 4 days. Storage Stage 1—Depletion Sample Diets to Achieve the Supercompensation Day 1: Exhausting exercise to deplete muscle glycogen in Effect. TABLE 23.10 provides a sample meal plan for carbohy- specific muscles drate depletion (stage 1) and carbohydrate loading (stage 2) Ϫ Days 2, 3, 4: Low-carbohydrate intake (60Ð100 g и d 1; high preceding an endurance event. percentage of protein and lipid in daily diet) Limited Applicability. Carbohydrate loading’s benefits Stage 2—Carbohydrate loading to exercise performance apply only to intense aerobic activities и Ϫ1 Days 5, 6, 7: High-carbohydrate intake (400Ð700 g d ; lasting longer than 60 minutes. Exercise lasting less than normal percentage of protein in daily diet) 60 minutes requires only normal carbohydrate intake and glyco- Competition day 12,115,165,189,197 High-carbohydrate precompetition meal gen reserves. For example, carbohydrate loading did not benefit trained runners in a 20.9-km (13-mile) run compared with a run following a low-carbohydrate diet. Similarly, no ergogenic effect emerged for time trial performance, heart Athletes should learn all they can about carbohydrate rate, and rating of perceived exertion (RPE) for endurance- loading before manipulating dietary and exercise habits to trained cyclists in a 100-km trial that simulated continuous achieve a supercompensation effect. If an athlete decides to changes in exercise intensity typical of competition.38 supercompensate after weighing the pros and cons, the new For sports competition and exercise training, a daily diet food regimen should proceed in stages during training, not for that contains about 60 to 70% of calories as carbohydrates the first time before competition. For example, the athlete provides adequate muscle and liver glycogen reserves. This should start with a long run followed by a high-carbohydrate diet ensures about twice as much muscle glycogen as a typical diet. A detailed log should record how the dietary manipula- diet of 45 to 50% carbohydrate. For well-nourished athletes, tion affects performance. A record of subjective feelings the supercompensation effect remains relatively small. During should include exercise depletion and replenishment phases. intense training, athletes who do not upgrade daily calorie and With positive results, the athlete can try the entire series— carbohydrate intakes to meet energy demands can experience depletion, low-carbohydrate diet, and high-carbohydrate chronic muscle fatigue and staleness.62

TABLE 23.10 • Sample Meal Plan for Carbohydrate Depletion and Carbohydrate Loading Preceding an Endurance Event Stage 1 Stage 2 Meal Depletion Carbohydrate Loading

Breakfast 0.5 cup fruit juice 1 cup fruit juice 2 eggs 1 bowl hot or cold cereal 1 slice whole-wheat toast 1 to 2 muffins 1 glass whole milk 1 Tbsp butter Lunch 6 oz hamburger 2Ð3 oz hamburger with bun 2 slices bread 1 cup juice salad (normal size) 1 orange 1 Tbsp mayonnaise and salad 1 Tbsp mayonnaise dressing pie or cake (one 8-in slice) 1 glass whole milk 1 cup yogurt, fruit, or cookies Snack 1 cup yogurt 1Ð1.5 pieces of chicken, baked Dinner 2Ð3 pieces of chicken, fried 1 cup vegetables 1 baked potato with sour cream 0.5 cup sweetened pineapple 0.5 cup vegetables iced tea (sugar) iced tea (no sugar) 1 Tbsp butter 2 Tbsp butter 1 glass chocolate milk with 4 cookies Snack 1 glass whole milk

During stage 1, the intake of carbohydrate approaches 60 g or 240 kCal; in stage 2, the carbohydrate intake increases to 400Ð700 g or about 1600Ð2800 kCal. 97818_ch23.qxd 8/4/09 4:47 PM Page 574

574 Section 4 Enhancement of Energy Transfer Capacity 250 Glycogen Supercompensation Enhanced by –1 t Prior Creatine Supplementation w A synergy exists between glycogen storage and creatine 200 supplementation. For example, preceding glycogen loading

kg w et with a 5-day creatine loading protocol (20 g per day) pro- . duced 10% greater glycogen packing in the vastus lateralis muscle than achieved with only glycogen loading.220 More 150 than likely, increases in creatine and cellular volume with cre- y l units atine supplementation facilitate subsequent storage of muscle glycogen. 100 Negative Aspects of Carbohydrate Loading The addition of 2.7 g of water with each gram of glyco- 50 gen makes it a heavy fuel compared with equivalent energy stored as fat. Athletes often feel “heavy” and uncomfortable with this added water weight; any extra load also directly y cogen (mmol) glucos

Gl adds to the energy cost of weight-bearing activities. The extra 0 weight may negate any potential benefits from increased Preloading Postloading glycogen storage. On the positive side, water liberated during Men Women glycogen breakdown aids in temperature regulation, which Figure 23.18 • Muscle glycogen concentrations pre- and benefits exercise in hot environments. post-carbohydrate loading (12 g carbohydrate per kg lean The classic model for supercompensation may pose body mass) in exercise-trained men and women. (From James potential hazards for individuals with specific health problems. AP, et al. Muscle glycogen supercompensation: absence of a A severe chronic carbohydrate overload, interspersed with pe- gender-related difference. Eur J Appl Physiol 2001;85:533.) riods of high lipid and/or high protein intake, can increase blood cholesterol and urea nitrogen levels. High lipid intake often causes gastrointestinal distress plus poor recovery from Gender Differences in Glycogen Storage the exercise-depletion sequence of the loading procedure. and Catabolism in Exercise During the low-carbohydrate phase of loading, marked ketosis can occur in individuals who exercise while carbohydrate Gender-related differences in muscle glycogen super- depleted. Failure to eat a balanced diet also produces mineral compensation remain controversial. One study reported a and vitamin deficiencies, particularly of the water-soluble vi- relatively small 13% increase in the muscle glycogen con- tamins. The glycogen-depleted state reduces the ability to tent of women when they switched from a mixed diet to a train, possibly leading to a detraining effect during portions of 281 high-carbohydrate diet. Other research indicated that the loading sequence. Dramatically reducing dietary carbohy- women do not increase glycogen storage when dietary car- drate for 3 or 4 days also could set the stage for lean tissue bohydrate increases from 60 to 75% of total caloric in- loss because muscle protein serves as gluconeogenic substrate 256 take. Importantly, this increase in carbohydrate intake as to maintain blood glucose levels in the glycogen-depleted a percentage of total calories represents considerably less state. total carbohydrate intake relative to lean body mass for women than for men. FIGURE 23.18 illustrates that equalizing Modified Loading Procedures daily carbohydrate intake for endurance-trained men and women at 12 g per kg of lean body mass for 3 consecutive A less stringent modified loading procedure outlined in days produced no gender differences in glycogen loading. FIGURE 23.19 eliminates many potential negative aspects of the These and other findings show that men and women pos- classic glycogen-loading sequence. The protocol increases sess an equal capacity to accumulate muscle glycogen when glycogen synthase activity without requiring dramatic glyco- fed comparable amounts of carbohydrate relative to lean gen depletion with exercise as with the classic loading proce- body mass.255,257 Women oxidize more lipid and less carbo- dure; it increases glycogen storage to nearly the same level. hydrate and protein compared with men during endurance The 6-day protocol does not require prior exercise to exhaus- 54,94,125 ú exercise. The increase in fat oxidation is associated tion. Rather, the athlete trains at about 75% of VO2max with higher intramyocellular lipid content and use as well (85% HRmax) for 1.5 hours and then, on successive days, as greater adipocyte lipolysis. The greater fat oxidation for gradually reduces (tapers) exercise duration. During the first women during submaximal endurance exercise seems to 3 days, carbohydrates represent about 50% of total calories. occur partly through a sex hormoneÐmediated enhancement Three days before competition, the diet’s carbohydrate con- of lipid-oxidation pathways.255 tent increases to 70% of total energy intake. 97818_ch23.qxd 8/4/09 4:47 PM Page 575

CHAPTER 23 Special Aids to Exercise Training and Performances 575 –1

t 250 Diet and exercise regimen w 1 week before marathon

100 100 Percenta Rest 200 kg w et

80 day . 75

60 g e carbo h ydrate 150 50 40 100 25 20 Exercise duration (min) Exercise duration 0 0 50 123456Race Days day 0 Muscle gl y cogen level (mmol Preloading Postloading Exercise time Dietary carbohydrate Figure 23.20 • Muscle glycogen concentration of the vastus Figure 23.19 • A modified approach to carbohydrate lateralis before (preloading) and after 180 seconds of near- loading. Recommended combination of diet and exercise for maximal intensity cycling exercise followed by 1 day of high- overloading muscle glycogen stores in the week before an carbohydrate intake (postloading). (From Fairchild TJ, et al. endurance contest. Exercise time is gradually reduced during Rapid carbohydrate loading after short bout of near maximal- the week, while the diet’s carbohydrate content increases for intensity exercise. Med Sci Sports Exerc 2002;34:980.) the last 3 days. (From Sherman WM, et al. Effect of exercise- diet manipulation on muscle glycogen and its subsequent insulin function, yet its precise mechanism of action remains un- utilization during performance. Int J Sports Med 1981;2:114.) clear. Insulin promotes carbohydrate transport into cells, augments fatty acid catabolism, and triggers cellular enzyme activity that facilitates muscle protein synthesis. Chronic INTEGRATIVE QUESTION chromium deficiency can increase blood cholesterol and de- What advice would you give to a sprint athlete crease the body’s sensitivity to insulin, thus raising the risk for who plans to carbohydrate load for competition? type 2 diabetes. Some adult Americans consume less than the 50 to 200 ␮g of chromium considered the estimated safe and adequate daily dietary intake (ESADDI). This occurs largely because chromium-rich foods—brewer’s yeast, broccoli, wheat Rapid Loading Procedure: A One-Day Requirement. germ, nuts, liver, prunes, egg yolks, apples with skins, aspara- The 2 to 6 days required to achieve supranormal muscle glyco- gus, mushrooms, wine, and cheese—do not usually form part of gen levels represents a limitation of typical carbohydrate-loading the regular diet. Food processing also removes substantial procedures. The desired loading effect occurs with a shortened chromium from foods. In addition, strenuous exercise and asso- duration that combines a brief bout of high-intensity exercise with ciated high-carbohydrate intake promote urinary chromium only 1 day of high-carbohydrate intake. Endurance-trained ath- losses, thus increasing the potential for chromium deficiency. letes cycled for 150 seconds at an exercise intensity of 130% For athletes with chromium-deficient diets, dietary modification ú VO2max followed by 30 seconds of all-out cycling. In the recov- to increase chromium intake or prudent use of chromium sup- Ϫ1 ery period, the men consumed 10.3 g и kg body mass of high plements seems appropriate. glycemic carbohydrate foods. Biopsy data presented in FIGURE 23.20 indicated that glycogen in the vastus lateralis mus- Numerous Alleged Benefits cle increased from a 109.1 mmol и kgϪ1 preloading average to 198.3 mmol и kgϪ1 after only 24 hours. This 82% increase in Touted as a “fat burner” and “muscle builder,” glycogen storage equaled or exceeded values reported by others chromium is one of the most hyped minerals in the health using a 2- to 6-day regimen. The short-duration loading proce- foodÐfitness literature. Supplemental intake of chromium, ␮ dure benefits individuals who do not wish to disrupt normal usually as chromium picolinate, often reaches 600 g daily. training with the time required and potential negative aspects of This chelated picolinic acid combination supposedly yields longer loading protocols.234 better chromium absorption than the inorganic salt chromium chloride. Millions of Americans believe the unsubstantiated Chromium claims of health food faddists, television infomercials, and exercise zealots that additional chromium promotes muscle The trace mineral chromium serves as a cofactor (as trivalent growth, curbs appetite, fosters body fat loss, and even length- chromium) for a lowÐmolecular-weight protein that potentiates ens life. Advertising targets chromium to bodybuilders and 97818_ch23.qxd 8/4/09 4:47 PM Page 576

576 Section 4 Enhancement of Energy Transfer Capacity other resistance-trained athletes as a safe alternative to ana- picolinate supplementation with a typical preseason training bolic steroids to favorably change body composition. program with identical training without supplementation.282 Chromium supplements supposedly potentiate insulin action Loss of muscle mass commonly affects older individu- to increase amino acid anabolism in skeletal muscle. This be- als, so potential ergogenic effect on muscle from chromium lief persists despite data that chromium supplements exert no supplementation should emerge readily in this age group. effect on glucose or insulin concentrations in nondiabetic in- This did not occur for older men involved in high-intensity dividuals.5 resistance training; a high chromium picolinate dosage Generally, studies suggesting beneficial effects of (924 ␮g и dϪ1) did not augment muscle size, strength, or chromium supplements on body fat and muscle mass infer power or FFM accretion above the unsupplemented condi- body composition changes from changes in body weight (or tion.41 Obese personnel enrolled in the United States unvalidated anthropometric measurements). One study ob- Navy’s mandatory remedial physical-conditioning program served that supplementing daily with 200 ␮g (3.85 ␮mol) of who consumed an additional 400 ␮g of chromium picoli- chromium picolinate for 40 days produced a small increase in nate daily showed no greater loss in body weight or per- FFM (estimated from skinfold thickness) and decrease in centage body fat or increase in FFM than a group receiving body fat in young men who resistance trained for 6 weeks.85 a placebo.261 The researchers provided no data to show increased muscular A comprehensive double-blind study examined the strength. Another study reported increases in body mass with- effects of a daily chromium supplement (3.3 to 3.5 ␮mol as out changes in strength or body composition in previously either chromium chloride or chromium picolinate) or a untrained female college students (no change in males) placebo for 8 weeks during resistance training in 36 young who received a daily 200-␮g chromium supplement during men. For each group, dietary intakes of protein, magnesium, 12 weeks of resistance training compared with unsupple- zinc, copper, and iron equaled or exceeded recommended lev- mented controls.119 els during training; subjects also maintained adequate base- Other research evaluated the effects of a chromium sup- line dietary chromium intakes. Supplementation increased plement of 200 ␮g daily on muscle strength, body composi- serum chromium concentration and urinary chromium excretion, and chromium excretion in 16 untrained males during tion equally regardless of its ingested form. TABLE 23.11 shows 12 weeks of resistance training.114 Muscular strength im- that compared with placebo treatment, chromium supplemen- proved 24% for the supplemented group and 33% for the tation did not affect training-related changes in muscular placebo group during training. No changes occurred in any of strength, FFM, or muscle mass. the body composition variables. The group receiving the supplement did show higher chromium excretion than controls Not Without a Potential Downside after 6 weeks of training. The researchers concluded that chromium supplements provided no ergogenic effect on any Chromium competes with iron for binding to transferrin, measured variable. Furthermore, supplementing with 800 ␮g the plasma protein that transports iron from ingested food and of chromium picolinate (plus 6 mg of boron) proved no more damaged red blood cells for delivery to tissues in need. The effective than a maltodextrin placebo to enhance lean tissue chromium picolinate supplement for the group whose data ap- gain or promote fat loss during resistance training.4 Daily pear in Table 23.11 reduced serum transferrin (a measure of supplementation with 400 ␮g of chromium picolinate for adequacy of current iron intake) compared with chromium chlo- 9 weeks did not promote weight loss in sedentary obese ride or placebo treatments. Conversely, other researchers ob- women; it actually caused weight gain during the treatment served that giving middle-aged men 924 ␮g of supplemental period.107 chromium daily as chromium picolinate for 12 weeks did not af- In support of chromium supplementation, greater body fat fect hematologic measures or indices of iron metabolism or iron loss (no increase in FFM) occurred in subjects “recruited from status.40 We are unaware of studies that have evaluated the a variety of fitness and athletic clubs” who consumed 400 ␮g of safety of long-term chromium supplementation or the ergogenic chromium daily over 90 days than in subjects who received a efficacy of supplementing in individuals with suboptimal placebo.139 Hydrostatic weighing and DEXA techniques as- chromium status. Concerning the bioavailability of trace miner- sessed body composition. However, body compositional data als in the diet, excessive dietary chromium inhibits zinc and iron from hydrostatic weighing do not appear in the report, and the absorption. At the extreme, this could induce iron-deficiency DEXA-derived analysis indicated average body fat values of anemia, blunt the ability to train intensely, and negatively affect 42% for both control and experimental subjects, an extraordi- exercise performance requiring high-level aerobic metabolism. nary level of obesity for members of fitness clubs. Collegiate Further potential bad news emerges from studies in football players who received daily 200-␮g supplements of which human tissue cultures that received extreme doses of chromium picolinate for 9 weeks showed no changes in body chromium picolinate showed eventual chromosomal damage. composition and muscular strength from intense weight train- Critics contend that such high laboratory dosages would not ing compared with controls receiving a placebo.52 Similar find- occur with supplement use in humans. Nonetheless, one could ings of no benefit on body composition and exercise argue that cells continually exposed to excessive chromium performance emerged from a 14-week study of NCAA (e.g., long-term supplementation) accumulate this mineral Division I wrestlers that compared combined chromium and retain it for years. 97818_ch23.qxd 8/7/09 3:54 PM Page 577

CHAPTER 23 Special Aids to Exercise Training and Performances 577

TABLE 23.11 • Effects of Two Different Forms of Chromium Supplementation on Average Values for Anthropometric, Bone, and Soft-Tissue Composition Measurements Before and After Resistance Training Placebo Chromium Chloride Chromium Picolinate

Pre Post Pre Post Pre Post

Age (y) 21.1 21.5 23.3 23.5 22.3 22.5 Stature (cm) 179.3 179.2 177.3 177.3 178.0 178.2 Weight (kg) 79.9 80.5a 79.3 81.1a 79.2 80.5 ⌺4 skinfold thickness (mm)b 42.0 41.5 42.6 42.2 43.3 43.1 Upper-arm girth (cm) 30.9 31.6a 31.3 32.0a 31.1 31.4 Lower-leg girth (cm) 38.2 37.9 37.4 37.5 37.1 37.0 FFMFM (kg)c 62.9 64.3a 61.1 63.1a 61.3 62.7a Bone mineral (g) 2952 2968 2860 2878 2918 2940 Fat-free body mass (kg) 65.9 67.3a 64.0 65.9a 64.2 66.1a Fat (kg) 13.4 13.1 14.7 15.1 14.7 14.5 Body fat (%) 16.4 15.7 18.4 18.2 18.4 17.9

From Lukaski HC, et al. Chromium supplementation and resistance training: effects on body composition, strength, and trace element status of men. Am J Clin Nutr 1996;63:954. a Significantly different from pretraining value. b Measured at biceps, triceps, subscapular, and suprailiac sites. c Fat-free, mineral-free mass.

Creatine concentration, 125 mM [range 90 to 160 mM] per kg dry muscle). About 40% exists as free creatine; the remainder combines Meat, poultry, and fish provide a rich source of creatine, con- readily with phosphate to form PCr. Type II, fast-twitch muscle taining 4 to 5 g of creatine per kg of food. The body synthe- fibers store about 4 to 6 times more PCr than ATP. As emphasizes only about 1 g of this nitrogen-containing organic sized in Chapter 5, PCr serves as the cells’ “energy reservoir” to compound daily from the nonessential amino acids arginine, provide rapid phosphate-bond energy to resynthesize ATP (more glycine, and methionine in the kidneys, liver, and pancreas. rapid than ATP regenerated in glycogenolysis) in the reversible The animal kingdom contains the richest creatine-containing reaction: foods, placing vegetarians at a distinct disadvantage for ready sources of exogenous creatine. Skeletal muscle contains ap- creatine kinase proximately 95% of the body’s total 120 to 140 g of creatine. PCr ϩ ADP ÐÐÐÐÐÐÐÐÐÐÐ: Cr ϩ ATP Creatine sold in supplemental form as creatine monohy- PCr also shuttles intramuscular high-energy phosphate be- drate (CrH O) comes as a powder, tablet, capsule, and stabi- 2 tween the mitochondria and muscle filament cross-bridge sites lized liquid. Adding phosphate salts to the CrH O molecule 2 that initiate muscle action. Maintaining a high sarcoplasmic creates phosphocreatine (PCr), a less frequently used form of ATP:ADP ratio by energy transfer from PCr plays an important creatine supplementation. Supplements in this form produce the role in maximum effort lasting up to 10 seconds. This exercise same training effects on body mass, muscular strength, and duration places high demands on ATP resynthesis that exceed FFM (estimated from skinfolds) as creatine ingested in mono- energy transfer from intracellular macronutrient breakdown. hydrate form.195 Creatine can be purchased over-the-counter or Improved energy transfer capacity from PCr also lessens reliance mail order as a nutritional supplement (but without guarantee of on energy from anaerobic glycolysis with associated increase in purity). Ingesting a liquid suspension of creatine monohydrate at intramuscular Hϩ and decrease in pH from lactate accumula- the relatively high dosage of 20 to 30 g per day for 2 weeks in- tion.11 Because of limited intramuscular PCr, it seems reasonable creases intramuscular concentrations of free creatine and PCr up that any PCr increase should accomplish the following: to 30%. These levels remain high for weeks after only a few days of supplementation.126,169 Sports governing bodies do not 1. Accelerate ATP turnover to maintain power output consider creatine an illegal substance. during short-term muscular effort. 2. Delay PCr depletion. 3. Diminish dependence on anaerobic glycolysis and Important Component of High-Energy decrease subsequent lactate formation. Phosphates 4. Facilitate muscle relaxation and recovery from re- Creatine passes through the digestive tract unaltered for ab- peated bouts of intense, brief effort via faster ATP sorption into the bloodstream by the intestinal mucosa. Just about and PCr resynthesis; rapid recovery allows continued all ingested creatine incorporates into skeletal muscle (average higher-level power output. 97818_ch23.qxd 8/4/09 4:47 PM Page 578

578 Section 4 Enhancement of Energy Transfer Capacity

TABLE 23.12 • Selected Studies Showing Increases in Exercise Performance Following Creatine Monohydrate Supplementation Reference Exercise Protocol Exercise Performance

d Isokinetic, unilat, knee 5 bouts of 30 ext, w/1-min rest Less decline in peak torque production during extensions (180¼иsϪ1) periods bouts 2, 3, and 4 e Running 4Ð300 m w/4-min rest periods Improved time for final 300- and 1000-m runs 4-1000 m w/3-min rest periods Improved total time for 4Ð1000-m runs; reduction in best time for 300- and 1000-m runs a Cycle ergometry Ten 6-s bouts w/1-min rest Better able to maintain pedal frequency during (140 revиminϪ1) periods second 4Ð6 of each bout f Cycle ergometry Five 6-s bouts w/30-s recovery Better able to maintain pedal frequency near end (140 revиminϪ1) followed by one 10-s bout of 10-s bout b Cycle ergometry Three 30-s bouts w/4-min rest Increase in peak power during bout 1 and (80 revиminϪ1) periods increase in mean power and total work during bouts 1 and 2 c Bench press 1-RM bench press and total reps Increase in 1-RM; increase in reps at 70% of at 70% 1-RM 1-RM g Bench press 5 sets bench press w/2-min rest Increase in reps completed during all 5 sets periods g Jump squat 5 sets jump squat w/2-min rest Increase in peak power during all 5 sets periods

a Balsom PD, et al. Creatine supplementation and dynamic high-intensity intermittent exercise. Scand J Med Sci Sports 1995;3:143. b Birch R, et al. The influence of dietary creatine supplementation on performance during repeated bouts of maximal isokinetic cycling in man. Eur J Appl Physiol 1994;69:268. c Earnest CP, et al. The effect of creatine monohydrate ingestion in anaerobic power indices, muscular strength and body composition. Acta Physiol Scand 1995;153:207. d Greenhaff PL, et al. Influence of oral creatine supplementation on muscle torque during repeated bouts of maximal voluntary exercise in man. Clin Sci 1993;84:565. e Harris RC, et al. The effect of oral creatine supplementation on running performance during maximal short-term exercise in man. J Physiol 1993;467:74P. f Soderlund K, et al. Creatine supplementation and high-intensity exercise: influence on performance and muscle metabolism. Clin Sci 1994;87(suppl):120. g Volek JS, et al. Creatine supplementation enhances muscular performance during high-intensity resistance exercise. J Am Diet Assoc 1997;97:765. From Volek JS, Kraemer WJ, Creatine supplementation: its effect on human muscular performance and body composition. J Strength Cond Res 1996;10:200.

Documented Benefits in Humans Creatine monohydrate supplements substantially increase muscle creatine content and performance in high-intensity Creatine supplementation received notoriety as an exercise, particularly repeated intense muscular effort ergogenic aid when British sprinters and hurdlers used it in 173,209,210,221,265,278 (TABLE 23.12). FIGURE 23.21 illustrates the er- the 1992 Barcelona Olympic Games. Creatine supplementa- gogenic effects of creatine supplementation on total work tion at recommended levels exerts the following three effects: accomplished during repetitive sprint cycling performance. 1. Improves performance in muscular strength and Physically active but untrained males performed sets of maxi- power activities mal 6-second bicycle sprints interspersed with various recovery 2. Augments short bursts of muscular endurance periods (24, 54, or 84 s) to simulate sport conditions. 3. Provides for greater muscular overload to augment Performance evaluations took place under creatine-loaded (20 g training effectiveness per day for 5 days) or placebo conditions. Supplementation in- No serious adverse effects from creatine supplementa- creased muscle creatine (48.9%) and PCr (12.5%), which pro- tion for up to 4 years have been reported.232 Anecdotes indi- duced a 6% increase in total work accomplished (251.7 kJ cate a possible association between creatine supplementation presupplement vs. 266.9 kJ creatine loaded) compared to the and cramping in multiple muscle areas during competition or placebo group (254.0 kJ pretest vs. 252.3 kJ placebo). Creatine lengthy practice in American football players. This effect may supplements have benefited an on-court “ghosting” routine of 223 result from (1) altered intracellular dynamics because of in- simulated positional play of competitive squash players. creased levels of free creatine and PCr or (2) osmotically in- Supplementation also augments repeated sprint cycle perform- duced enlarged cell volume (greater cellular hydration) from ance after 30 minutes of constant load, submaximal exercise in the 173 the muscle fibers’ increased creatine content. Gastrointestinal heat, without adversely affecting thermoregulatory dynamics. tract disturbances (nausea, indigestion, and difficulty absorb- One research study evaluated a creatine dose of 30 g daily ing food) have been linked to exogenous creatine ingestion. It for 6 days in trained runners under two conditions: (1) four re- remains unclear whether the ergogenic effect differs in vegetar- peated 300-m runs with a 4-minute recovery and (2) four 1000- 117 ians and meat eaters.237 m runs with a 3-minute recovery. Compared with placebo 97818_ch23.qxd 8/4/09 4:47 PM Page 579

CHAPTER 23 Special Aids to Exercise Training and Performances 579 recovery of muscle contractile capacity, enabling athletes to maintain repeated efforts of high-intensity exercise and train- 300 ing. A facilitated rate of muscle relaxation may also contribute to the ergogenic action of creatine supplementation.267 Besides benefiting weightlifting and bodybuilding, improved immediate anaerobic power output capacity aids sprint run- 280 ning, swimming, kayaking, cycling, jumping, football, and volleyball. Oral creatine supplementation combined with heavy-resistance training affects cellular processes in a man- 260 ner that increase protein deposition within the muscle’s contractile mechanism.287 This response could explain any increase in muscle size and strength associated with creatine supplementation. 240 Creatine supplementation does not improve cardiovas-

Work done (kJ) Work cular and metabolic responses during continuous incremental treadmill running or performance that requires a high level of aerobic energy transfer.10,110 220

Are There Risks? Potential dangers of short-term creatine supplementation 200 have been studied in healthy individuals, particularly on car- Creatine Placebo diac muscle and kidney function (creatine degrades to creatinine before excretion in urine). Creatine consumed 20 g per Pre-loading Post-loading day for 5 consecutive days produced no detrimental effect on blood pressure, insulin action, plasma creatine, plasma CK Figure 23.21 • Effects of creatine loading versus placebo on activity, or renal function, measured by glomerular filtration total work accomplished during repetitive sprint-cycling rate, kidney permeability, and total protein and albumin ex- performance. (From Preen CD, et al. Effect of creatine cretion rates.153,175,185,200 Only limited information exists loading on long-term sprint exercise performance and about the effects of long-term, high-dose supplementation metabolism. Med Sci Sports Exerc 2001;33:814.) with creatine. For healthy subjects, no differences in plasma contents and urinary excretion rates for creatinine, urea, and albumin emerged between control subjects and individuals treatment, creatine supplementation improved performance who consumed creatine for up to 5 years.199 Glomerular filtra- under both conditions with the most impressive gains in repeated tion rate, tubular reabsorption, and glomerular membrane per- 1000-m runs. Supplementing with 20 g of creatine daily for meability also remained normal with long-term creatine use. 4 days also benefited anaerobic capacity in three 30-second Individuals with suspected renal malfunction should refrain Wingate tests with a 5-minute rest between trials. For Division I from creatine supplementation because of the potential for football players, creatine supplementation with resistance train- exacerbating the disorder.205 ing increased body mass, lean body mass, cellular hydration, and muscular strength and performance.21 Similarly, supplementa- Age Effects Uncertain tion augmented muscular strength and size increases during 12 weeks of resistance training.287 The enhanced hypertrophic Whether creatine supplementation augments the training response with supplementation and resistance training possibly response in older individuals remains equivocal. For 70-year- results from accelerated myosin heavy-chain synthesis. For old men, a creatine supplementation loading phase (0.3 g per resistance-trained men classified as “responders” to creatine kg body mass for 5 days) followed by a daily maintenance supplementation (i.e., a creatine increase Ն32 mmol и kg dry phase (0.07 g per kg body mass) increased lean tissue mass, wt muscleϪ1), 5 days of supplementation increased body weight leg strength, muscular endurance, and average power of the and FFM, and peak force and total force during repeated legs during resistance training to a greater extent than a pla- maximal isometric bench-presses.146 For men classified as cobo.51 Similarly, creatine supplements benefit muscular per- “nonresponders” to supplementation (i.e., creatine increase formance in normally active older men.104 In contrast, no Յ21 mmol и kg dry wt muscleϪ1), no ergogenic effect occurred. enhancement in resistance-training response to creatine inges- FIGURE 23.22 outlines possible mechanisms for en- tion occurred among sedentary and weight-trained older hanced exercise performance and training response by ele- adults.24 These results were attributed to an age-related de- vating intramuscular free creatine and PCr. Consuming a cline in creatine transport efficiency. Short-term creatine sup- high dose of creatine helps replenish muscle creatine follow- plementation per se, without resistance training, does not ing intense exercise. This metabolic “reloading” promotes increase muscle protein synthesis or FFM.191 97818_ch23.qxd 8/4/09 4:47 PM Page 580

580 Section 4 Enhancement of Energy Transfer Capacity

MKK Supplements Exogenous Creatine Monohydrate

Pre-exercise Intramuscular Hydration status PCr availability Cr and PCr of cell

Dependence Pre-exercise on glycolysis Cr availability Protein synthesis

(Lactate) [H+] Flux through Cr Diameter of kinase reaction type II fibers

PCr resynthesis Fat-free pH body mass [PCr] at start of next exercise bout Figure 23.22 • Mechanisms to explain why increased intracellular creatine (Cr) and phosphocreatine Delayed onset Training (PCr) might enhance intense, short- of fatigue Intensity term exercise performance and the exercise-training response. (Modified from Volek JS, Kraemer WJ. Creatine Short-term supplementation: its effect on muscular human muscular performance and performance body composition. J Strength Cond Res 1996;10:200.)

resistance or agility training resulted partly from increases in Effects on Body Mass and Body Composition fat- or bone-free body mass unrelated to an increase in total Increases in body mass between 0.5 and 5.2 kg often ac- body water.152 company creatine supplementation, independent of changes in Resistance-trained men matched for physical character- testosterone or cortisol concentrations.77,130,279 How much of istics and maximal strength randomly received a placebo or the weight gain occurs from the anabolic effect of creatine on creatine supplement. Supplementation consisted of 25 g daily muscle tissue synthesis, retention of intracellular water from in- followed by maintenance at 5 g daily. Both groups engaged in creased creatine stores, or other factors remains unclear. heavy resistance training for 12 weeks. FIGURE 23.23A shows Creatine intake during resistance training (4-d pretrain- the greater training-induced increase in body mass and FFM ing dosage, 20 gиdϪ1, followed by 5 gиdϪ1 during training) for the creatine-supplemented group compared with controls. by young adult females increased maximal strength of trained Greater maximum bench press and squat strength increases muscles (20Ð25%), maximal intermittent exercise capacity of occurred in the creatine group than in controls (FIG. 23.23B). the arm flexors (10Ð25%), and FFM (6%) compared with the Creatine supplementation induced greater muscle fiber hyper- placebo condition.264 Additional muscle water content could trophy with resistance training, indicated by greater enlarge- account for a portion of the FFM increase. A 2.42-kg body ment in types I (35 vs. 11%), IIA (36 vs. 15%), and IIAB mass gain associated with creatine supplementation and muscle fiber cross-sectional areas (35 vs. 6%; FIG. 23.22C). 97818_ch23.qxd 8/4/09 4:47 PM Page 581

CHAPTER 23 Special Aids to Exercise Training and Performances 581 Creatine Loading

7 Many creatine users pursue a loading phase by ingesting 20 to 30 g of creatine daily for 5 to 7 days. Individuals who

g e (k ) 6 consume vegetarian-type diets show the greatest increase in

h an 5 muscle creatine levels because of their low dietary creatine con- * tent. Particularly large increases characterize individuals with 4 normally low basal levels of intramuscular creatine.36,43 A main- 3 tenance phase follows the loading phase. During this time, the athlete supplements with as little as 2 to5gofcreatine daily. 2 Practical questions for the athlete desiring to elevate in- 1 tramuscular creatine levels concern the magnitude and time course of intramuscular creatine increase with supplementa-

Body composition c 0 A BM FFM Fat tion, dosage needed to maintain the creatine increase, and rate of creatine loss or “washout” when supplementation ceases. 40

To provide insight into these questions, researchers studied 35 two groups of men. In one experiment, six men ingested 20 g 30 of creatine monohydrate (approximately 0.3 g per kg of body g e (k ) mass) for 6 consecutive days and then stopped the supple- 25 *

h an mentation. Biopsies assessed muscle creatine levels before 20 supplement ingestion and at days 7, 21, and 35. Similarly, 15 g t h c nine men took 20 g of creatine monohydrate daily for 6 con- 10 secutive days. Instead of discontinuing supplementation, they

S tren 5 reduced dosage to 2 g daily (approximately 0.03 g per kg body mass) for an additional 28 days. FIGURE 23.24A shows 0 B Squat Bench that total muscle creatine concentration increased approximately 20% after 6 days. Without continued supplementation,

) 1800 2 muscle creatine content gradually declined to near baseline in 35 days. The group that continued to supplement with re- 1500 * * duced creatine intake for an additional 28 days maintained 1200 * muscle creatine at the higher level (FIG. 23.24B). For both groups, the increase in total muscle creatine 900 content during the initial 6-day supplementation period aver- iber area (μm 600 aged about 23 mmol per kg of dry muscle; this represented about 20 g (17%) of total creatine ingested. A similar 20% in- g e in f 300 crease in total muscle creatine concentration occurred with only a 3-g daily supplement. However, the increase occurred

Ch an 0 C I IIA IIAB IIB more gradually and required 28 days rather than 6 days with Muscle fiber type the 6-g supplement. A rapid way to creatine-load skeletal muscle requires ingesting 20 g of creatine monohydrate daily for 6 days; switch- Creatine Placebo ing to a reduced 2-g per day dosage keeps these levels elevated for up to 28 days. If rapidity of loading is of little Figure 23.23 • Effects of 12 weeks of creatine supplementation plus heavy-resistance training on changes in concern, supplementing with 3 g daily for 28 days achieves (A) body mass (BM), fat-free body mass (FFM), and body fat; the same high levels. (B) muscular strength in the squat and bench press; and (C) cross-sectional areas of specific muscle fiber types. The Carbohydrate Ingestion Augments Creatine Loading. placebo group did identical training and received an Consuming creatine with a sugar-containing drink in- equivalent quantity of powdered cellulose in capsule form. creases creatine uptake and storage in skeletal muscle * Change significantly greater compared to the placebo 241 group. (From Volek JS, et al. Performance and muscle fiber (FIG. 23.25). For 5 days, subjects received either 5 g of crea- adaptations to creatine supplementation and heavy-resistance tine four times daily or a 5-g supplement followed 30 minutes training. Med Sci Sports Exerc 1999;31:1147.) later by 93 g of a high-glycemic simple sugar four times daily. The creatine-only group increased muscle PCr (7.2%), free The larger volume of weight lifted during weeks 5 to 8 by the creatine (13.5%), and total creatine (20.7%). Much larger in- creatine supplement group suggests that higher quality train- creases occurred for the creatine-plus-sugarÐsupplemented ing sessions mediated more favorable adaptations in FFM, group (14.7% for PCr, 18.1% for free creatine, and 33.0% for muscle morphology, and strength performance. total creatine). Creatine supplementation alone did not affect 97818_ch23.qxd 8/4/09 4:47 PM Page 582

582 Section 4 Enhancement of Energy Transfer Capacity

160 ) ) –1

–1 * 150 * 30 kg dm . kg dm

. 140

130

20 120

110 * Total creatine (mM Total 100 A Day 0Day 7Day 21 Day 35 10 160 )

–1 150

* ** (mM Increase in muscle concentration 0

kg dm 140 Phosphocreatine Creatine Total creatine .

130 Cr ingestion Cr + CHO ingestion

120 Figure 23.25 • Increases in dry muscle (dm) concentrations of phosphocreatine (PCr), creatine (Cr), and total creatine in 110 one group after 5 days of Cr supplementation and in another group after 5 days of Cr and carbohydrate (CHO) Total creatine (mM Total supplementation. Values represent averages. * Significantly 100 greater than creatine-only supplementation. (From Green AL, B Day 0Day 7Day 21 Day 35 et al. Carbohydrate ingestion augments skeletal muscle creatine accumulation during creatine supplementation in Figure 23.24 • A. Total muscle creatine concentration in six humans. Am J Physiol 1996;271:E821.) men who consumed 20 g of creatine for 6 consecutive days and then stopped the supplement. Muscle biopsies done subjects performed maximal intermittent knee-extension exer- before ingestion (day 0) and on days 7, 21, and 35. B. Total cise to fatigue on an isokinetic dynamometer. Creatine supple- muscle creatine concentration in nine men who ingested mentation, with or without caffeine, increased intramuscular 20 g of creatine for 6 consecutive days and then ingested 2 g PCr (evaluated by nuclear magnetic resonance spectroscopy) of creatine daily for the next 28 days. Muscle biopsies taken between 4 and 6%. Dynamic torque production also increased before ingestion (day 0) and on days 7, 21, and 35. Values refer to averages per dry mass (dm). * Significantly different 10 to 23% with creatine compared with the placebo. Consuming from day 0. (From Hultman E, et al. Muscle creatine loading caffeine totally negated creatine’s ergogenic effect. To optimize in men. J Appl Physiol 1996;81:232.) creatine’s benefits, athletes should abstain from caffeine- containing foods and beverages for several days prior to and insulin secretion, whereas adding sugar elevated plasma in- during creatine loading, training, and competition. sulin levels. More than likely, augmented creatine storage with a creatine-plus-sugar supplement resulted from insulin- Some Research Shows No Benefit mediated glucose transport into skeletal muscle, which facili- Not all research confirms positive effects of creatine tated creatine transport into muscle fibers. supplementation. Ergogenic effects may not emerge under the Stop Caffeine When Using Creatine. Caffeine negates following seven conditions, but the reason for the discrepan- the ergogenic effect of creatine supplementation. To evaluate cies remains unknown: the effect of preexercise caffeine ingestion on intramuscular 1. In untrained subjects performing a single 15-second creatine stores and intense exercise performance, subjects con- bout of sprint cycling60 sumed either a placebo, a daily creatine supplement (0.5 g и kgϪ1 2. In trained subjects performing bouts of sport-specific body mass), or the same daily creatine supplement plus caffeine physical activities such as swimming, cycling, and (5 mg и kgϪ1 body mass) for 6 days.263 Under each condition, running37,88 97818_ch23.qxd 8/4/09 4:47 PM Page 583

CHAPTER 23 Special Aids to Exercise Training and Performances 583 3. In trained and untrained older adults131,290 Exercise Benefits Inconclusive 4. In resistance-trained individuals250 Consuming MCTs does not inhibit gastric emptying, as 5. In trained rowers71 does common fat, but conflicting research supports their use 6. During rapid weight loss187 in exercise.136,137,271,275 In early studies, subjects consumed 7. When short-term supplementation does not increase 88,183 380 mg of MCT oil per kg of body mass 1 hour before exer- muscle PCr ú 66 cising at 60 to 70% of VO2max for 1 hour. Plasma ketone levels generally increased, but the exercise metabolic mixture Lipid Supplementation with Medium-Chain did not change compared with a placebo trial or a trial after Triacylglycerols subjects consumed a glucose polymer. Catabolism of 30 g of Do high-fat foods or lipid supplements elevate plasma fatty MCTs (estimated maximal amount tolerated in the gastrointestinal tract) consumed before exercising contributed only acid levels to increase energy availability from fat during pro- 134 longed aerobic exercise? Several factors affect the answer to 3 to 7% to the total exercise energy requirement. this question. First, consuming triacylglycerols composed of predominantly long-chain fatty acids (12 to 18 carbons) de- INTEGRATIVE QUESTION lays gastric emptying. This negatively affects the rapidity of Discuss the importance of the psychologic or fat availability and slows fluid and carbohydrate replenish- “placebo” effect to evaluate claims for the ment, both crucial factors in intense endurance exercise. effectiveness of particular nutrients, chemicals, or Second, after digestion and intestinal absorption (normally procedures as ergogenic aids. 3 to 4 h), long-chain triacylglycerols reassemble with phos- pholipids, fatty acids, and a cholesterol shell to form fatty droplets called chylomicrons. These substances travel slowly Subsequent research investigated possible metabolic and to the systemic circulation via the lymphatic system. They ergogenic effects of consuming 86 g of MCT (surprisingly eventually empty into the systemic venous blood in the neck well tolerated by subjects). Six endurance-trained cyclists region by way of the thoracic duct. Through the action of the ú rode for 2 hours at 60% of VO2peak while ingesting 2 L of enzyme lipoprotein lipase that lines capillary walls, chylomi- 4.3% MCT emulsion, 10% glucose plus 4.3% MCT emulsion, crons in the bloodstream readily hydrolyze to provide free or a 10% glucose solution during exercise. They then per- fatty acids and glycerol for use by peripheral tissues. The formed a simulated 40-km cycling time trial. FIGURE 23.26 relatively slow rate of gastric emptying and subsequent diges- shows the effects of the different beverages on average speed tion, absorption, and assimilation of long-chain triacylglyc- in the time trials. Replacing the carbohydrate beverage with erols makes this energy source an undesirable supplement to only MCTs produced an 8% decrement in performance (in augment energy metabolism during exercise. agreement with another study),136 but the combined carbohy- Medium-chain triacylglycerols (MCTs) provide a more drate plus MCT solution consumed throughout exercise pro- rapid source of fatty acid fuel. MCTs are processed oils, fre- duced a 2.5% improvement in cycling speed compared with quently produced for patients with intestinal malabsorption the two other conditions. This ergogenic effect occurred with and tissue-wasting diseases. Marketing for the sports enthusi- reduced total carbohydrate oxidation at a given level of oxy- ast hypes MCTs as “fat burners,” “energy sources,” “glycogen gen consumption, higher final circulating FFA and ketone sparers,” and “muscle builders.” Unlike longer-chain triacyl- levels, and lower final glucose and lactate concentrations. glycerols, MCTs contain saturated fatty acids with 8 to 10 car- The small ergogenic enhancement by MCT supplemen- bon atoms along the fatty acid chain. During digestion, lipase tation probably occurred because this exogenous source of in the mouth, stomach, and intestinal duodenum hydrolyzes fatty acids contributes relatively little to the total energy ex- MCTs to glycerol and medium-chain fatty acids (MCFAs). penditure (and total fat oxidation) during sustained exer- Their water solubility allows MCFAs to move rapidly across cise.135 MCT ingestion does not stimulate release of bile, the the intestinal mucosa directly into the bloodstream (portal gall bladder’s fat-emulsifying agent. Thus, cramping and di- vein) without first being transported as chylomicrons by the arrhea often accompany excess intake of this lipid. It provides lymphatic system as long-chain triacylglycerols require. Once little ergogenic effect. at the tissues, MCFAs move readily through the plasma membrane where they diffuse across the inner mitochondrial membrane for oxidation—they enter the mitochondria largely Pyruvate independent of the carnitineÐacyl-CoA transferase system. Ergogenic effects have been extolled for pyruvate, the three- The speed of cellular uptake and mitochondrial oxidation con- carbon end product of the cytoplasmic breakdown of glucose in trasts with the relatively slower transfer and oxidation rate of glycolysis. Exogenous pyruvate, as a partial replacement for long-chain fatty acids. MCTs do not usually store as body fat dietary carbohydrate, supposedly augments endurance per- because of their relative ease of oxidation. Ingesting MCTs formance and promotes fat loss. Pyruvic acid, a relatively un- rapidly elevates plasma FFAs, making it plausible that these stable chemical, causes intestinal distress, so various forms of lipids might spare liver and muscle glycogen during aerobic the salt of this acid (sodium, potassium, calcium, or magnesium exercise. pyruvate) are manufactured in capsule, tablet, or powder form. 97818_ch23.qxd 8/4/09 4:47 PM Page 584

584 Section 4 Enhancement of Energy Transfer Capacity endurance by 20% compared with exercise with a 100-g supplement of an isocaloric glucose polymer.244,245 The pyruvateÐ 40 DHA mixture increased cycle ergometer time to exhaustion of the legs by 13 minutes (66 vs. 79 min), while upper-body arm-cranking exercise time increased by 27 minutes (133 vs. 160 min). Exercising with the pyruvateÐDHA mixture reduced 38 local muscle and overall body ratings of perceived exertion * 219

) compared with the placebo condition.

–1 Proponents of pyruvate supplementation maintain that

h ** . elevated extracellular pyruvate augments glucose transport 36 into active muscle. Enhanced “glucose extraction” from the blood provides the important energy source to sustain high- intensity aerobic exercise while conserving intramuscular glycogen stores.128 When the individual’s diet contains a nor- 34 mal level of carbohydrate (approximately 55% of total energy intake), pyruvate supplementation also increases preexercise 245

verage speed (km verage muscle glycogen levels. Both of these effects—higher pre- A exercise glycogen levels and facilitated glucose uptake and 32 oxidation by active muscle—benefit endurance exercise similarly as preexercise carbohydrate loading and glucose feed- ings during exercise exert ergogenic effects.

Body Fat Loss 30 10% CHO+ 10% CHO 4.3% MCT 4.3% MCT Subsequent research by the same investigators who showed ergogenic effects of pyruvate supplementation indi- Figure 23.26 • Effects of carbohydrate (CHO; 10% cates that exogenous pyruvate intake augments body fat loss solution), medium-chain triacylglycerol (MCT; 4.3% when accompanied by a low-energy diet. Obese women in a emulsion), and carbohydrate ϩ MCT (10% CHO ϩ 4.3% metabolic ward maintained a liquid 1000-kCal daily energy in- MCT) ingestion during exercise on simulated 40-km time-trial take (68% carbohydrate, 22% protein, 10% lipid). Adding 20 g cycling speeds after 2 hours of exercise at 60% of V˙ O2peak. of sodium pyruvate plus 16 g of calcium pyruvate (13% of en- * Significantly faster than 10% CHO trials; ** Significantly ergy intake) daily for 3 weeks induced greater weight loss (13.0 faster than 4.3% MCT trials. (From Van Zyl CG, et al. Effects vs. 9.5 lb) and fat loss (8.8 vs. 5.9 lb) than a control group on of medium-chain triglyceride ingestion on fuel metabolism the same diet who received an equivalent amount of extra en- and cycling performance. J Appl Physiol 1996;80:2217.) ergy as glucose.246 These findings complement the researchers’ previous study with obese subjects that showed that adding Dosage recommendations range between a total of 2 and DHA and pyruvate (substituted as equivalent energy for glu- 5 g of pyruvate spread throughout the day and taken with cose) to a severely restricted low-energy diet facilitated body meals. One capsule usually contains 600 mg pyruvate. The weight and fat loss (without increased nitrogen loss).247 The calcium form of pyruvate also contains approximately 80 mg precise role of pyruvate in facilitating weight loss remains un- of calcium with 600 mg of pyruvate. Some advertisements known. Consuming pyruvate may stimulate small increases in recommend dosage of one capsule per 20 pounds of body futile metabolic activity (metabolism not coupled to ATP pro- weight. Manufacturers also combine creatine monohydrate duction) with a subsequent wasting of energy. and pyruvate; 1 g of creatine pyruvate provides about 80 mg Adverse side effects of a 30- to 100-g daily pyruvate in- of creatine and 400 mg of pyruvate. Recommended pyruvate take include diarrhea and gastrointestinal gurgling and dosages range from 5 to 20 g per day. Pyruvate content in the discomfort. Until studies from independent laboratories re- normal diet ranges from 100 to 2000 mg daily. The largest produce existing findings for exercise performance and body dietary amounts occur in fruits and vegetables, particularly fat loss, one should view the effectiveness of pyruvate supple- red apples (500 mg each), with smaller quantities in dark beer mentation with caution. (80 mg per 12 oz) and red wine (75 mg per 6 oz). Summary Endurance Performance 1. The term ergogenic aid describes substances or pro- Several reports indicate beneficial effects of exogenous cedures that improve physical work capacity, physi- pyruvate on endurance performance. Two double-blind, cross- ologic function, or athletic performance. over studies by the same laboratory showed that 7 days of daily 2. The strongest research studies apply a randomized, supplementation of a 100-g mixture of pyruvate (25 g) plus double-blind, placebo-controlled design. 75 g of dihydroxyacetone (DHA, another three-carbon com- 3. Different levels of evidence permit grading the pound of glycolysis) increased upper- and lower-body aerobic strengths of research studies. 97818_ch23.qxd 8/4/09 4:47 PM Page 585

CHAPTER 23 Special Aids to Exercise Training and Performances 585 4. Anabolic steroids compose a group of pharmaco- 17. A physiologic rationale for why warm-up should logic agents frequently used for ergogenic purposes. enhance exercise performance includes benefits on These drugs function like the hormone testosterone; muscle-shortening velocity and efficiency, enhanced they increase muscle size, strength, and power with oxygen delivery and use, and facilitated transmis- resistance training in some individuals. sion of nerve impulses. Limited research supports ␤ 5. The 2-adrenergic agonists clenbuterol and al- the benefits of warm-up beyond a positive psycho- buterol increase skeletal muscle mass and slow fat logic component. gain in animals to counter aging, immobilization, 18. Moderate warm-up proves beneficial immediately malnutrition, and tissue-wasting pathology. A nega- before sudden, strenuous exercise by reducing my- tive finding showed hastened fatigue during short- ocardial work and augmenting coronary blood flow term, intense muscle actions. when exercise begins. 6. Debate exists about whether administration of 19. Breathing hyperoxic gas during exercise extends growth hormone to healthy individuals augments endurance by increasing oxygen consumption, muscular hypertrophy when combined with resist- reducing blood lactate, and lowering pulmonary ance training. Health risks exist for those who abuse ventilation. Using this procedure before or after this chemical. exercise provides no ergogenic effect. 7. Dehydroepiandersterone (DHEA), a relatively weak 20. Carbohydrate loading augments endurance in pro- steroid hormone synthesized from cholesterol by the longed submaximal exercise. Athletes should be adrenal cortex, steadily decreases throughout adult- well informed about this procedure because of po- hood, prompting individuals to supplement, hoping tential negative effects. to counteract the effects of natural aging. DHEA 21. A modification of the classic loading procedure pro- does not produce an ergogenic effect. vides the same high level of glycogen storage without 8. Research indicates no effect of androstenedione dramatic alterations in the diet and exercise routine. supplementation on basal serum concentrations of 22. No benefits emerge from chromium supplements on testosterone or training response for muscle size and training-related changes in muscular strength, strength and body composition. physique, or muscle mass for individuals with ade- 9. No ergogenic effects exist for healthy subjects from quate dietary chromium intake. chronic oral amino acid supplements on hormone 23. Creatine supplements increase intramuscular crea- secretion, training responsiveness, or exercise tine and PCr, enhance brief anaerobic power output performance. capacity, and facilitate recovery from repeated bouts 10. Hormonal dynamics from carbohydrate and/or of intense effort. protein supplementation immediately following a 24. Medium-chain triacylglycerols (MCTs) enhance fat resistance-exercise workout suggests an ergogenic oxidation and conserve glycogen during endurance effect on training responsiveness. exercise. This procedure does enhance performance 11. Amphetamines, or pep pills, do not aid exercise by an additional 2.5%. performance or psychomotor skills, other than by a 25. Pyruvate supplementation purportedly augments placebo effect. Adverse effects include drug de- endurance performance and promotes fat loss, but a pendency, headache, dizziness, confusion, and gas- definitive conclusion concerning its effectiveness trointestinal distress. requires research verification. 12. Caffeine ingestion typically exerts an ergogenic effect by extending endurance in aerobic exercise References are available online at from increased fat use for energy and conservation http://thepoint.lww.com/mkk7e. of glycogen reserves. 13. No compelling evidence supports ginseng supplementation to benefit physiologic function or exer- On the Internet cise performance. Significant health risks World Anti-Doping Agency: Prohibited List accompany ephedrine use. www.wada-ama.org/en/prohibitedlist.ch2 14. Concentrated buffering solutions consumed before Official website of the Olympic Movement exercise improve anaerobic exercise performance. www.olympic.org/ 15. Further research must determine the benefits and American College of Sports Medicine risks of glutamine, phosphatidylserine, and ␤- www.acsm.org/ hydroxylÐ␤-methylbutyrate to provide a “natural” U.S. Drug Enforcement Administration anabolic boost with resistance training. www.usdoj.gov/dea/ 16. The additional blood volume and increased red cell U.S. Drug Enforcement Administration: mass and concentration from red blood cell reinfu- Drug Abuse Prevention and Control www.usdoj.gov/dea/pubs/csa.html sion contribute to a larger maximum cardiac output and an increase in the blood’s oxygen-carrying U.S. Food and Drug Administration ˙ www.fda.gov capacity and VO2max.