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EXERCISE PHYSIOLOGY The Methods and Mechanisms Underlying Performance by Stephen Seiler (sections 1 - 12) ( http://home.hia.no/~stephens/exphys.htm ) Table of Contents The Endurance Performance Model 3 1) The Heart 5 a) Basic physiology i) More about how the heart adapts to training 8 ii) Maximal oxygen consumption - The VO2max 9 iii) The impact of body dimensions on endurance performance 15 iv) Gender differences in endurance performance & training 17 b) Myocardial Adaptations to Training 27 c) Aging and Cardiovascular Function 31 d) Understanding Heart Rate and Exercise 32 2) Skeletal Muscles a) Basic Skeletal Muscle Physiology 36 b) Training Adaptations in Skeletal Muscle 40 c) Aging Effects on Skeletal Muscle 45 d) Skeletal Muscle Fiber Type 47 i) The muscle biopsy 49 ii) Skeletal muscle fiber type - part 2 50 3) Putting the Pieces Together a) Lactate threshold? 53 b) Efficiency, economy and endurance performance 58 c) Brain - body link and adaptation to training 63 4) Aging, Exercise and Short Term Power 68 5) Principles of Training - Revisited 84 6) The time course of training adaptations 92 Cycling Articles: Physiology 1 Table of Contents 7) Understanding interval training 98 8) Elite male distance runners 22 yrs later 111 9) Strength training and endurance performance 118 10) Muscle hypertrophy vs hyperplasia - a review 123 11) Ventilation and endurance performance 134 12) Aerodynamics and Cycling 148 13) Lactate Threshold 154 14) Weight training for cyclists 175 15) Racing Techniques 198 16) Cycling Climbing Tips 204 Cycling Articles: Physiology 2 Table of Contents THE ENDURANCE PERFORMANCE MODEL Whether you run, row, ski or cycle, the goal is always the same; you are attempting to maximize your ACHIEVED PERFORMANCE VELOCITY. All endurance sports demand some combination of three components: 1) High oxygen transport capacity, 2) High fatigue resistance in working muscles, and 3) High efficiency of transfer of physiological work to mechanical movement. Every endurance athlete brings to the starting line some combination of Performance Power (1 and 2). The third variable, Efficiency of Power Transfer (3) links the engine to the specific movement task. These variables combine to determine Potential Performance Velocity. Finally, on a given race day, performance potential is influenced by psychological factors and the accuracy of pacing. The end product is ACHIEVED PERFORMANCE VELOCITY, a personal best, a Masters record etc. Conservatively, we can list dozens of factors that impact endurance performance. To make things more complex (and interesting), these factors are not independent, but influence each other. Finally, each particular sport discipline puts specific demands and constraints on the system through both the specific resistance to movement that must be overcome, and the race distance or duration. Given all of this complexity, it is helpful to have a unifying model. So, I am presenting one here for you that you can refer back to when you read other articles. This model summarizes the currently accepted understanding of the physiological limitations to endurance performance. In other words, it is the current paradigm. Perhaps time will show that other factors should be included, or some of these deemphasized. For now, this model seems to fit the data well. The concept of the figure or this discussion is certainly not original. It summarizes the findings of nearly 100 years of physiological and performance research. An excellent article on this subject based on research he has directed or assisted, and a fairly similar figure, were produced by Edward Coyle PhD (Exercise and Sport Science Reviews, vol.23, p25, 1995. Williams and Wilkens, Publishers.) Michael Joyner M.D. also wrote some excellent synthesizing material on the issue of physiological limitations on performance (running). Journal of Applied Physiology 70:683-687, 1991. Cycling Articles: Physiology 3 The Endurance Performance Model Now, as complicated as the figure above may appear, it is still a simplification. Underneath the physical and anatomical components we could add: 1) genotype, 2) genetically determined responsiveness to training, 3) nutrition, 4) immunological resistance to stress, 5) testosterone level, 6) intensity of training stimulus, 7) frequency of training, 8) years of training load, etc. It is a fantastic puzzle to explore, but remember, the solution is different for each person. Good Luck. Cycling Articles: Physiology 4 The Endurance Performance Model 1) HEART FACTS AND TRIVIA What's in a Name? The existence of the heart was well known to the Greeks, who gave it the name Kardia, still surviving in modern words such as cardiac and tachycardia. Aristotle believed that the heart was the seat of the soul and the center of man. Romans modified Kardia to Cor, the latter word still surviving in "cordial greetings". The old Teutonic word herton was also derived from Cor and gives us heart via the medieval heorte. Where is it Located? Dumb question right? Well if you answered left chest, you're wrong! The heart is situated almost dead center in the middle of the chest nested between the two lungs. However, the apex or tip of the heart is shifted towards the left chest wall and hits against the ribs during contraction. Consequently, the rhythm is best detected on the left side, just below the pectoralis. How Big is it? It is generally about the size of your fist. This is not really very big when you think about the job it does. In some animals, such as horses, the heart size to body size ratio is much greater. This helps explain why horses are such great endurance athletes! The heart is also bigger in champion endurance athletes, due to genetics and training. (see subcategory-(b) below). The average untrained heart can pump about 15 to 20 liters of blood per minute at max. Large, elite athletes may have a maximal cardiac output of nearly 40 liters / min. This is a huge flow moving through a pump the size of your fist! To get some perspective on these output rates, go to your kitchen sink and turn on the water full blast. Now find a milk jug or something that will give you a measure of volume. I bet you find that your faucet does not flow as fast as the heart can pump. In a sense, the heart is really two linked pumps, the left heart and the right. Both sides pump the same amount of blood, but to different locations at different pressures. The right side pump (right ventricle) pumps oxygen- depleted blood that has returned from the body to the lungs for reoxygenation. This is a short trip and requires little pressure development, so the right ventricle is rather thin walled, like a fireplace bellows. The left side (left ventricle) is the real workhorse, pumping oxygenated blood that has returned Cycling Articles: Physiology 5 1. Heart Facts and Trivia from the lungs (the right and left side of the heart are thus connected) to the entire body. That means moving blood through an incredible maze of blood vessels from the top of the head to the toes! Consequently it must develop more pressure each beat (about 120mm Hg at rest). The left heart muscle is thicker as a result, just as your bicep would become thicker if you had to lift heavy weights with it all day. How Does it Pump Blood? Classically, we have been taught that the heart squeezes blood through the aorta by decreasing the external circumference of the heart. This view is supported by the fact that during heart surgery (with the chest cracked open), the heart does pump in this manner. However, under normal conditions, the heart operates within the thoracic cavity in a closed, fluid-filled volume. There is now growing evidence to indicate that during exercise, the heart performs more like a piston or a vacuum pump, with little change in external circumference. As we learn more about the dynamics of heart function, it is evident that this model is critical to the efficiency of the heart as a pump. More recent models of heart performance indicate that the heart takes advantage of vacuum effects and fluid inertia as heart rate increases during exercise. One reason why artificial hearts have performed so poorly is that they have tried to use a design based on erroneous assumptions about how the human heart pumps. The classical view of heart pumping mechanics will die slowly, due to its pervasiveness. However, it seems reasonable to say that the heart performs more like a vacuum pump than like a hand squeezing the juice out of a lemon. When the heart pumps, the ventricular wall’s outer diameter changes little, while the internal diameter dramatically decreases as blood is ejected from the ventricle. What Controls the Heart Rate? Now this is a tough question to answer without using a little physiology lingo. Unlike skeletal muscle, which is under voluntary control, the heart is an involuntary muscle. Most of us cannot just tell our heart to slow down or speed up (biofeedback training not withstanding). The beating frequency (heart rate) is controlled by the balance of stimulation coming from the sympathetic and parasympathetic branches of the Autonomic Nervous System. Both nervous inputs to the heart converge on a small area of tissue in the right atrium called the Sino-atrial (SA) node. Parasympathetic (rest and recover) stimulation tends to slow down the rate, while sympathetic (fight or flight) input increases the rate (and the force of contraction). Normally, there is a balance between the two Cycling Articles: Physiology 6 1. Heart Facts and Trivia inputs leaning toward the parasympathetic side. However, even without any nervous input, the heart will beat automatically due to some unique features of its membrane physiology.