Physiological Aspects of Exercise and Sport - Case Study Example

INDEX Introduction to muscle tissue Physiology of muscle contraction Mechanism of muscle contraction(sliding filament theory) Uses of stretching ant its impacts on sports person. (includes introduction to static and dynamic stretching, static Vs dynamic stretching) Theories of stretching, uses of stretching and effects of stretching. CONTRACTION OF SKELETAL MUSCLE Introduction to muscle tissue:- Functionally, muscle cells are specially organized to convert chemical energy to mechanical work. In a vertebrate body three types of muscles are identified. They are striated, non striated and cardiac muscles. Striated are the skeletal muscles. These striated muscles form the main bulk of the body muscular system and are found to attach to bones. hence they are named as skeletal muscles. They act quickly and are under the voluntary control. Muscle issue is made up of excitable cells that result in the contraction of the muscle. Muscle tissue is made up of numerous microfilaments composed of actin and myosin which are contractile proteins. striated muscles are composed of muscle fibres.each fiber is cylindrical and is enclosed in a sheath called sarcolemma. The multiple nuclei arise from the fact that each muscle fiber develops from the fusion of many cells called myoblasts. The number of fibers is probably fixed early in life. This is regulated by myostatin, a cytokine that is synthesized in muscle cells. Myostatin suppresses skeletal muscle development. Some athletes and other remarkably strong people have been found to carry one mutant myostatin gene. These discoveries have already led to the growth of an illicit market in drugs supposedly able to suppress myostatin.In adults, increased strength and muscle mass comes about through an increase in the thickness of the individual fibers and increase in the amount of connective tissue. The fibers attract more myoblasts by releasing the cytokine interleukin 4 (IL-4). Anything that lowers the level of myostatin also leads to an increase in fiber size. myofibril contains alternate dark and light bands. the darks band is known as anisotropic band or A-band, these is a paler zone called as isotropic band or I-band. A-band is formed by thick filaments of myosin. myosin filaments have cross bridges. I-band is formed by thin filaments composed of proteins called actin, tropomysin and troponin.they extend into the A-band among myosin filaments. Physiology of muscle contraction:-Muscle cell contains a series of components that are directly associated with contraction. The Cell Membrane - Controls what enters and leaves the cell. Contains regulatory proteins that are influenced by hormones like epinephrine (adrenalin) and insulin. The blood concentration of these hormones greatly influences fuel utilization by the muscle cell. Contractile Proteins - The contractile machinery of a muscle fiber is organized into structural units called sarcomeres. Muscle length is determined by how many sarcomeres are lined up in series, one next to the other. Muscle thickness ultimately depends on how many sarcomeres line up in parallel (one on top of the other). The sarcomere structures consist of two important proteins, actin and myosin (about 85% by volume). Several other important proteins called troponin and tropomyosin, and proteins with cool names like titin, nebulin, and desmin help to hold these units together. The sarcomeres are organized as many thin myofibrils. The Cytosol. This is the aqueous fluid of the cell. It provides a medium for diffusion and movement of oxygen, new proteins, and ATP within the cell's interior. Mitochondria - The organelles in each muscle cell that contain oxidative enzymes consume oxygen during exercise. mitochondria may look more like an interconnected network than little isolated oval "powerhouses". Mitochondria convert the chemical energy contained in fat and carbohydrate to ATP, the only energy source that can be used directly by the cell to support contraction. Ultimately, glucose and fat molecules (and certain amino acids) break down and combine with oxygen to form ATP, carbon dioxide, water, and heat energy. The carbon dioxide and excess water leave the body. The ATP generated provides a usable energy source for muscle contraction and other cell functions. Clearly, each by-product of energy metabolism has significance to the exercising athlete. Mechanism of muscle contraction(sliding filament hypothesis)According to the theory, the contraction of the sarcomere depends upon two types of filaments, and during muscle contraction, actin filaments slide over the myosin filaments resulting in shortening of sarcomere. when a nerve impulse reaches the neuro muscular junction, the sarcolemma of that muscle cells gets depolarized. the depolarization extends into the sarcoplasmic reticulum and releases calcium ions into the sarcoplasm.these calcium ions diffuse into the sarcoplasm and alters the chemical properties of myosin filaments. the calcium binds to troponin if thin filaments thus conformational changes occurs in tropomyosin and in actin.preparing them to react with ATP, myosin. Thus the thin filaments are activated when exposed to active sites. the cross bridges of myosin binds with the active filament at active sites to form actomyosin complex. then actomyosin tilts or swings towards the H-zone. as a result, the thin filaments of actin are pulled over the myosin filaments.actin activates myosin-ATPase which results in the release of energy from ATP for the movement of myosin cross bridges.ATP binds with the myosin cross bridges causing the detachment of head of crossed bridge from the actin filament. then the cross bridge swings back to original position called recovery stroke. during muscle contraction, the width of A-band remains same but the I-band decrease in length. Use of stretching and its impact on sports performance:- the type of stretching chose to perform before activity will have an affect on the performance and injury levels of the athletes.'Static stretching involves reaching forward to a point of tension and holding the stretch.' Static stretching has been used through out the years for two main reasons: injury prevention and performance enhancement. Many of the best strength coaches support the use of dynamic stretching.' Dynamic stretching consists of functional based exercises which use sport specific movements to prepare the body for movement Research has shown that static stretching can be detrimental to performance and doesn't necessarily lead to decreases in injury.' Below are a few studies done on the topic of static stretching. New research has shown that static stretching decreases eccentric strength for up to an hour after the stretch.' Static stretching has been shown to decrease muscle strength by up to 9% for 60 minutes following the stretch and decrease eccentric strength by 7% followed by a specific hamstring stretch.dynamic strecthing involves moving parts of your body and gradually increasing reach, speed of movement, or both. Dynamic stretching consists of controlled leg and arm swings that take the athletes to the limits of their range of motion. There are two kinds of stretch receptors, one measures magnitude and speed and the other measures magnitude only.' Static flexibility improves static flexibility and dynamic flexibility improves dynamic flexibility which is why it doesn't make sense to static stretch prior to dynamic activity. There is considerable but not complete transfer of static stretching to dynamic stretching. Dynamic Flexibility increases core temperature, muscle temperature, elongates the muscles, stimulates the nervous system, and helps decrease the chance of injury. Most coaches, athletes and sports medicine personnel use stretching methods as part of the training routine for athletes. Flexibility has two important components: static and dynamic flexibility. Static flexibility describes range of motion without a consideration for speed of movement. This is the maximum range a muscle can achieve with an external force such as gravity or manual assistance. For example, holding a hamstring stretch at an end-of-range position. Dynamic flexibility describes the use of the desired range of motion at a desired velocity. Dynamic flexibility is the range athletes can produce themselves. For example, a javelin thrower or baseball pitcher needs a lot of shoulder rotational flexibility, but they also need to be able to produce it at rapid speeds of movement.Importance and impact of stretching Stretching also forms an integral part of rehabilitation programmes following injury. For example, it is accepted that a muscle tear will heal with scar tissue. This scar tissue tends to be functionally shorterhave more resistance to stretch than normal healthy muscle tissue. Therefore stretching is used at an appropriate time in the healing process to assist in lengthening this contracted scar tissue. flexibility improves posture and ergonomics. Our bodies have a tendency to allow certain muscles to tighten up which will affect our posture. Vladimir Janda, a Czech rehabilitation specialist, describes a group of muscles in the body that universally show a tendency towards tightness and also being overactive in movements. Some of these include the hamstrings, rectus femoris, TFL, piriformis, adductors, gastrocnemius and quadratus lumborum. These muscles are often implicated in postural syndromes causing musculoskeletal pain. Flexibility, because it allows good range of motion, may improve motor performance and skill execution. Skill execution and reduced risk of injury will be greatly enhanced if the body has the flexibility necessary for that particular sport. Flexibility can be limited by what are called 'active' or 'contractile' and 'passive' or 'non-contractile' restraints. Muscle contraction is one of these 'active/contractile' restraints. Flexibility can be limited by the voluntary and reflex control that a muscle exhibits while undergoing a stretch, in particular a rapid stretch that activates the 'stretch reflex'. As a muscle is rapidly stretched, a receptor known as a 'spindle' causes the muscle to reflexively contract to prevent any further stretch. If left unchecked, the stretch reflex would work to prevent elongation while the muscle was being stretched. A benefit of fast stretching is that the nervous system learns to accommodate by delaying the stretch reflex until closer to end of range of movement. Furthermore, a resting muscle does not always mean that it is resting. Muscles usually exist with a certain degree of muscle tone. An increase in tone will increase the inherent stiffness in muscles. the way actin and myosin remain bound and thus resist passive stretching of the muscle. The actin and myosin stay bound because of a constant low-level discharge in the nerves supplying that muscle. With actin and myosin unbound, a muscle should in theory be able to stretch to 150 per cent of its original length .'Passive/non-contractile' restraints in the form of connective tissues will also limit flexibility. The passive restraints include the connective tissues within and around muscle tissue (epimysium, perimysium and endomysium), tendons and fascial sheaths. The important microscopic structure to consider in passive tissues is collagen. Muscles need to be flexible to achieve peak performance and stretching is the most effective way for developing flexible muscles and tendons. Tight muscles may also cause loss of strength and power during sports or physical activity. Flexibility training may or may not include stretching exercises but includes exercises that alter the nervous system control of the muscles to allow greater range of motion to take place in the joints static stretching (relaxed passive) does increase flexibility but is not very effective in strengthening the muscle particularly at the end of range of motion. Muscle which is weak in the stretched position can easily be injured during exercise or sport activity. The static stretching also lacks the capacity to immediately reduce tension in very tight muscles. The key is to make the muscles stronger in the stretched position.a person can improve flexibility provided they increase the strength of their muscles. PNF type of stretching due to its use of static contraction increases strength. So, not only is the athlete becoming more flexible, he/she becomes stronger particularly in the extreme range of motion. In general fitness, flexibility is not as important as in professional sports. Unless you are into gymnastics, martial arts or other sports requiring extreme flexibility there is no need to go overboard on flexibility. Joint mobility and dynamic stretches are a good warm-up exercise as they improve dynamic flexibility which is vital in sports such as martial arts, gymnastics, athletics. At the end of exercise, when static type of stretching is applied it improves muscle recovery, relieves muscle tension and improves blood flow in the muscle. Stretching can also be used as part of a cool down routine. Another benefit of stretching is that it helps bring fresh blood supply to the muscle therefore increasing the oxygen content of the muscle cells. The increased blood supply helps flush out lactic acid. Stretching after exercise stimulates the transportation of amino acids into the muscle cells, accelerates protein synthesis inside the cell and inhibits protein degradation. Regular exercise reduces the incidence and magnitude of muscle soreness. For serious athletes the carefully controlled inclusion of some eccentric exercise in the training programme could be important in injury prevention. Several studies have shown that a single bout of eccentric exercise performed every week is enough to keep the muscles permanently adapted. The explanation for this protective effect of prior eccentric exercise probably involves several neural, connective tissue and cellular adaptations. Neural adaptations are related to increased muscle fibre recruitment during eccentric contractions. Connective tissue adaptations relate to a remodelling and/or an increase in intramuscular connective tissue. Cellular mechanisms of adaptation relate to the previously mentioned increase in the number of sarcomeres connected in series. as an athlete boosts their traing schedules, they almost always overuse their muscles causing imbalances, strains, in the soft muscle tissues. all athletes look forward to improve their performance, to this rigorous training schedules is done to enhance their skills strength and speed which leads to severe risk of injury.addotionally tragic is the fact that most of the athletes in their quest to improve; ignore pains and aches until they turn into serious injuries. the more a sports injury is ignored, the more susceptible it becomes to injury and strain. one other kind of muscle repair is after training sports massage can be taken.sportsmassage will help in release any build up tension and lactic acid in the overworked muscles so that oxygen and blood can return to the muscle system and therefore effectively repair the muscle sports massage helps an athlete to prevent injuries and strains caused due to overused of muscles. Excessive flexibility can be just as dangerous as not being flexible enough, as both will increase the risk of injury. In most sports flexibility, particularly active one, is key to good performance, so working on one's active flexibility and increasing strength in stretched out position in the agonists is essential. Stretching should be specific to the sport and the individual athlete. In conclusion, stretching is necessary for anyone involved in sports or physical activity and should be designed accordingly. Stretching program should be individualized based on person's level of conditioning and physical make-up. SOURCES:- Micheal J. Pelczar, JR. Tata McGrawhill publications-fifth edition. Muscular contraction ( Robert Malcolm Simmons) -1992 Complete guide to Symptoms, Illness & Surgery ( H. Winter Griffith) -2006 ( Health & fitness ) Willium D. McArdle Frank I. Katch -2006 Sporst Medicine for Specifc Ages and Abilities ( Nicola Maffulli ) -2001 Exercise Phychology ( Peter Seraganian ) -1993 ( BOOKS AVAILABLE AT BRITISH LIBRARY ). Read More