The Effects of Stretching Post Exercise and Delayed Onset Muscle Soreness
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Iowa State University Capstones, Theses and Creative Components Dissertations Spring 2019 Have we been stretching the truth? The effects of stretching post exercise and delayed onset muscle soreness Mackenzie Keil Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/creativecomponents Part of the Kinesiotherapy Commons, Movement and Mind-Body Therapies Commons, and the Physiotherapy Commons Recommended Citation Keil, Mackenzie, "Have we been stretching the truth? The effects of stretching post exercise and delayed onset muscle soreness" (2019). Creative Components. 203. https://lib.dr.iastate.edu/creativecomponents/203 This Creative Component is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Creative Components by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Mackenzie Keil BMS 599 4/12/2019 Have we been stretching the truth? The effects of stretching post exercise and delayed onset muscle soreness Committee: Dr. Michael Lyons, Dr. Alan Robertson, Dr. Gayle Brown 1 Abstract: Stretching is a commonly proposed mechanism used to prevent delayed onset muscle soreness (DOMS). Many coaches and medical professionals have always recommended to stretch after exercise to help reduce muscle soreness. Stretching reduces muscle tightness and can help improve flexibility which can help athletic performance. Another accepted belief involving stretching is that it is used to reduce lactic acid levels in the muscle which reduces soreness. There is not sufficient evidence to support either of these claims, however, stretching is commonly used and accepted throughout athletics and active individuals as a way to prevent or reduce muscle soreness. DOMS is muscle soreness that occurs 24-48 hours post-exercise. Eccentric exercise is the main cause to this soreness because it injures the cell membrane of sarcolemma. This injury leads to an acute inflammatory response and results in pain. Lactic acid build-up in the muscle is not the cause of muscle soreness. Pain is specifically the result of eccentric exercise. After reviewing glycolysis and the Cori Cycle, it is understood why lactic acid is not responsible for causing muscle soreness. This review of the literature investigates different studies involving stretching techniques and its effects on muscle soreness. The different types of stretching including ballistic, static, and PNF techniques were compared to each other determine their effects on DOMS and if one technique reduced soreness more than another. The amount of time a stretch was held was also taken into consideration. The literature concluded that stretching after exercise does not reduce muscle soreness caused by DOMS. It did not matter what type of stretching was done or how long the stretch was held. The stretching groups had the same level of soreness as the non-stretching groups. It is still important to stretch to maintain flexibility and reduce muscle tightness, but it has no effects on muscle soreness. 2 Introduction: Stretching is a common technique taught to help improve athletic performance. From a young age, it has been taught by parents, physical education, coaches, and medical professionals that stretching is a vital component to exercise. It has been embossed into everyone’s mind that stretching will not only improve performance, but it will help reduce muscle soreness. Additional reasons stretching is suggested is that it used to increase range of motion and decreases the risk of injury. It is also widely accepted that stretching post-exercise will decrease the lactic acid levels from the muscle and decrease pain. Coaches have been preaching this theory for many of years, but it is not clear why it was proposed that lactic acid builds up and causes muscle soreness. The main reason lactic acid it is thought to cause pain is because the lactic acid decreases the pH which can lead to injury. There is conflicting research on the true effects of stretching has on delayed onset muscle soreness (DOMS). Many research studies conclude that there is not enough evidence to say people should stop stretching or say people should stretch. In this review of the current literature, the effects that stretching post-exercise has on muscle soreness will be examined as well as what types of stretching are being recommended. Background: Stretching is known to cause relaxation in tense muscles by a method of shortening and lengthening the target muscle. It is a technique used to increase range of motion and flexibility in joints, which are the main components that allow movement to occur. Muscle tightness causes a decrease in range of motion and affects an individual’s movement. The tightness in the muscle is due to muscle tension which occurs by active tension or passive tension. Passive tension involves the muscle’s viscoelasticity and surrounding fascia, whereas active tension involves proprioceptors such as alpha and gamma motor neurons. (1) There are three types of neurons known as sensory, interneurons and motor neurons. Stretching involves the motor (efferent) neurons that are found in the ventral horn and send axons to skeletal muscle. The function of these motor neurons is to trigger a contraction in the target muscle. The two types of motor neurons are alpha and gamma motor neurons. The alpha motor neurons, when activated, release acetylcholine at the neuromuscular junction which leads to a muscle contraction. They are 3 activated by the interneurons and higher-level motor systems and innervate extrafusal muscle fibers. Gamma motor neurons innervate the muscle spindle. The muscle spindle is a proprioceptive sensory receptor that conveys information about the muscle length and rate of change. Specifically, the Ia sensory fiber within the muscle spindle is responsible for constantly monitoring the velocity of muscle change. The Ia fiber fires when the muscle is stretching and stops firing when muscle length stops changing. When the muscle spindle is contracted or stretched, this stretches the non-contractile portion of the spindle which prompts the sensory endings in the Ia fiber to send information to the spinal cord. This information includes the length of muscle and rate of change in length of the muscle. When the muscle length change stops, the Ia fiber will stop firing and adapt to the new muscle length. The stretch reflex occurs when a muscle spindle detects a fast rate of change in the muscle. The Ia fiber, which innervates the spindle, will then send this sensory information to the interneuron and stimulate the motor neuron of the same muscle to contract. Contracting the muscle will stop over elongation of the muscle and prevent injury. The Golgi tendon organ (GTO) is another proprioceptive sensory receptor that lies connected in the origin/insertion of a muscle/tendon as seen in Figure 1. It relays information about the muscle tendon tension or rate Figure 1 shows the connection between the Ia fiber and muscle spindle and the Ib fiber and GTO. of change of tension in the muscle. It relays this https://o.quizlet.com/WJaCaJfGU3FzOBtTe4VyLw .png information via the Ib sensory fiber. The Ib sensor fiber innervates the GTO and synapses on the interneuron. The function of the GTO is to sense change in muscle tension. When a muscle generates a force, the sensory endings of the Ib fiber become compressed. This leads to the opening of stretch-sensitive cation channels and causes depolarization generating a nerve impulse to the interneuron. The Golgi tendon reflex prevents the excessive tension in the muscle fibers to prevent injuring the muscle. The reflex occurs when a potentially damaging muscle force is detected by the GTO. The Ib fiber will send this sensory information to the inhibitory interneurons in the spinal cord. The interneurons will then inhibit the activity of the motor 4 neurons that control the muscle being contracted. This reduction in motor neuron activity will reduce the muscle contraction, causing relaxation and preventing a possible injury. (1) There are many types of stretching such as static, dynamic, ballistic and proprioceptive neuromuscular facilitation (PNF) as seen in Figure 2. Static stretching is the most commonly known type. It requires the person to lengthen the tight muscle until a stretched sensation is felt. This pose is then held from 10-60 seconds and then performed on the other side. Each major muscle group is typically only stretched once. Dynamic stretching involves movement and to get into full range of motion. The muscle is lengthened until stretch sensation is felt, but the position is not held for a long amount of time like static. The other difference between static and dynamic, is that the stretch is repeated multiple times and typically performed while walking. Ballistic stretching is a technique that uses the momentum of the body to force a limb into or past full range of motion. It is commonly seen on the sidelines by the athlete swinging their legs side to side, trying to kick higher each time. No research was found as to why these three stretching techniques were first brought into practice, but they have been widely accepted and used for a long time. Proprioceptive neuromuscular facilitation (PNF) works the agonist/antagonist properties of muscles. This means there is a target muscle, the one wanting to be stretched and an opposing muscle. This is type of stretch is typically performed by a medical professional, coach or partner. The provider will lengthen the target muscle until a stretch sensation is felt. The patient will then contract the opposing muscle, usually by pressing against providers hand, then contract the target muscle, relax and provider will further lengthen the target muscle. This is done two to three times per side and each relax-contract is only held about 5- 6 seconds.