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The Body & Muscle Groups

            There are three types of muscles in the human body; skeletal, smooth and cardiac.  In general, muscles are essentially major tissues whose function is to convert chemical energy in to mechanical work by contracting - the process of “squeezing” together large proteins (actin & myosin) to shorten muscle fibers.  Cardiac muscles are fundamentally muscles that cause the ventricle to contract during the pumping of blood while smooth muscles generally transport matter such as blood to other parts of the body through the process of peristalsis (contraction & expansion).  Both these muscles are involuntary – they are not consciously controlled.  For the purpose of this paper, the skeletal muscles will primarily be focused on.  The skeletal muscles, also dubbed striated muscles, are voluntary muscles which are attached to the skeleton.  In skeletal muscles, as a result of contraction, a force is applied to a certain area of the skeleton through tendons – connecting tissues between the skeleton and the muscle.  Muscle groups and the contraction & relaxation of skeletal muscle will further be discussed later.

             As mentioned previously contraction is essentially what occurs when muscle fibers shorten.  Skeletal muscle contractions are initiated by the release of calcium within the cell which is most likely due to electrical impulses from the central nervous system.  In order to carry out the muscle contraction, adenosine triphosphate (ATP) is required as a source of energy.  There are essentially four sources from which ATP can be synthesized, but synthesis will depend on whether the exercise is aerobic or anaerobic: dephosphorylation of creatine phosphate, glycogen, blood glucose & fatty acids, and fermentation.  There are two types of contractions; isometric and isotonic.  Isometric contractions occur when the muscle cannot shorten and the muscle exerts tension as opposed to isotonic contraction which occurs when the muscle shortens but the tension remains constant.  Both types of contraction will tear the muscle fibers, resulting in increased synthesis of the actin and myosin filaments.  The increased formation of the actin and myosin filaments cause thickening of muscle fiber and ultimately resulting in larger muscles, as discussed later.  Thus, both types of contractions effectively lead to muscle mass growth during weight training, but for the purpose of this assignment isotonic contraction will primarily be focused upon.   

            When the brain sends a nerve impulse to the muscles to start working, calcium pumps release calcium ions from the lateral sacks.  The calcium ions pull what are known as the tropinin-tropomyosin complex from the actin filament, allowing the actin molecule to bind to the myosin molecule.  After this binding process is complete, muscle contraction follows.  During muscle relaxation, calcium pumps pump the calcium ions released in the contraction process back into the lateral sacks.  Since the presence of the calcium ions are removed, the tropinin-tropomyosin complex is free to move back into the actin filament, therefore preventing the myosin and actin molecules from binding together.  

            Muscle cells contain many myofibrils (sacrostyles), which are fundamentally organelles that are bundles of filament and can further be broken down in to sarcomeres-the basic unit of contraction.  Sarcomeres are composed of thick and thin filaments, where the thick filaments are made up of myosin molecules (each molecule is composed of two protein strands twisted together- refer to figure 2.1) while the thin filament (actin filament) is composed primarily of actin proteins but also contains tropomyosin and troponin proteins.  As mentioned previously, as contraction occurs, the actin and myosin filaments slide past each other.  However, prior to this a cross-bridge occurs.  Cross-bridging is the attachment of the myosin head to the binding site of the actin filament.  During cross-bridging, the orientation of the actin filament relative to the myosin filament is changed.  This change in orientation provides a force to these filaments, and therefore the filaments slide relative to each other.  The myosin head then binds to an ATP molecule, breaking its bond with the actin filament.  This causes the muscle cell to return to its relaxed state (extension).

 Figure 2.1 – a molecule of myosin  

            While some muscles may be arranged to act together to achieve work, often the muscles are arranged in pairs such that as one muscle contracts, the other muscle extends.  This is known as flexion and extension, respectively.  For example, during the flexion of the concentration curl, as the bicep contracts, the tricep extends.  During the extension of the concentration curl, as the bicep extends, the tricep contracts.  

For each skeletal muscle, there is an origin and an insertion.  The origin is the tendon connecting the muscle to the stationary bone, while the insertion is the tendon connecting the muscle to the mobile bone.  During contraction, the muscle exerts a force on the mobile bone through the insertion tendon.  Upper body muscles will be primarily be focused on for the purpose of this assignment.  Refer to Figure 2.2 for a comprehensive diagram of the skeletal muscle system.


Muscle Growth  

The growth of muscles is due to muscle fibre hypertrophy but it is thought that hyperplasia also plays a role in muscle growth.  Muscle hyperplasia is essentially the increased number of fibres in the muscle due to splitting of the cells whereas hypertrophy is the increase in size of the muscle due to the enlargement in the size of the fibres.  There are two types of hypertrophy in the muscles; transient and chronic.  The main difference between the two is that transient hypertrophy is the increase in apparent size of the muscle due to fluid accumulation in the intracellular spaces of the muscle fibres while chronic hypertrophy is the increase in actual size of the muscle due to hyperplasia and the thickening of the individual muscle fibres.  

Generally the increase in size of muscle fibres is dependant on protein synthesis.  Once the muscle fibres sustain microtears, the process of muscle growth is induced.  Ultimately what occurs is that protein synthesis is increased due to a variety of hormones.  Testosterone, a steroid hormone, enters the muscle cell by diffusing across the cell membrane, and works together with a hormone receptor within the cell which then prompts gene transcription and protein formation.  Human growth hormones (hGH) are released from the anterior pituitary (a gland in the head), and triggers the production of insulin-like growth factors (IGF).  IGF causes the muscle cell to increase its uptake of amino acids and glucose to form protein while hGH causes nuclear division in the muscle cell without triggering mitosis and hence there are more nuclei to more rapidly synthesize protein.  Protein synthesis can also be initiated due to the release of insulin within the body.  The release of insulin can be stimulated by certain amino acids.  Thus, protein synthesis is increased largely due to these three hormones, and with a larger amount and a faster rate of synthesis, proteins can rebuild the muscle fibres thicker.

For further information regarding steroids such as testosterone, refer to section VIII.



Physical and Psychological Benefits of Exercising  

There are numerous ways that exercising can be beneficial in both physical and psychological aspects of life.

 Some of the more obvious physical benefits of exercising include less chance of death related to heart diseases and stroke, weight loss, get in shape and longer life span.  Inactivity is one of the worst causes of heart diseases, along with smoking, high cholesterol levels, and high blood pressure.  Exercise could help if not alleviate some heart problems present.  As the heart is used with increased intensity, the cardiac muscle gets stronger, more efficient, pumping more blood per contraction, and thus puts less strain on the body.  A recommended thirty minute medium-intensity exercise on most days of the week will reduce the risk of coronary diseases significantly. People who are active have a forty-five percent less chance of developing heart disease. A study done in 2002 reconfirmed the fact that even diminutive amounts of intense exercise could lower the cholesterol levels, while more exercise significantly lowers cholesterol levels.

Frequent exercise keep the arteries flexible, which improves blood flow and therefore keeps a regular blood pressure. Men who exercise merely one hour per day and five days per week, has a fifty gain percent less chance of getting a stroke.  

Lungs also benefit from regular exercise.  People with mild asthma gain from exercise by obtaining a larger breathing capacity. Even though 40% - 90% of asthma attacks are caused by exercising, exercises such as swimming, indoor running, and yoga are nevertheless good for asthma patients. A study showed that 66% of asthma patients who do yoga were successful in minimizing or eliminating the need for medicine. 

For strong muscles and bones, exercise is important.  As individuals age, muscles become less, but people who exercise are stronger and fitter than other people in their age group.  A 2003 study proves that running could be associated with a longer life and less disabilities.  

Exercising falls under 2 categories: strength training and cardiovascular training. The main goal of strength training is to build muscle mass while cardiovascular exercise achieves greater stamina by using light weights. Muscles build when they are put under strain. Exercising the main muscles groups for forty minutes 3-4 times a week is enough to increase muscle strength.  Strength and massive muscles could be gained by using heavy weights and doing fewer repetitions.  If the following symptoms are encountered, then overworking is possibly the cause: dizziness, constant fatigue, and frequent cold or the flu. Some of the positive effects of strength training would be: increasing muscle strength, increasing muscle size, more flexibility, balance, makes the bones stronger and denser, reduce risk of degrading diseases, help reduce fat levels, increases quality of life, and increasing the testosterone level.  Cardiovascular training, on the other hand, is one where an activity is usually done over a longer period of time. It includes walking, jogging, swimming, and many other exercises.  Cardiovascular training helps condition the heart and the lungs, ensuring a healthy and long life. Some other benefits of cardiovascular exercises include: a lean body, a strengthened heart, better cholesterol (more good vs. bad), reduces chances of getting colon cancer, reduced risk of getting diabetes, and a lower heart rate and blood pressure, and a enhanced quality of life.  

Psychological Benefits of exercising is essentially the mechanism behind how exercises help the exerciser psychologically is still a mystery, but is does have the following positive impacts on the exerciser: relieve stress and tension, improves self-esteem, boost blood flow to the brain, and just feeling better about yourself.  Physical exercise acts like a buffer against stress by minimizing the effect of stress on the body. Regular exercise also decreases anxiety by stabilizing it. As the workout/exercise is begun, anxiety actually rises, but levels off as the activity is continued. Five to thirty minutes after the workout has concluded, the anxiety level is lower than before. It has shown a greater impact on reducing the effects of anxiety than the drug meprobamate, a powder that is used to relax muscles, relieves anxiety as a tranquilizer, and an anticonvulsant. Also it has a vastly constructive impact on the human body by relaxation and lowering anxiety, the effects are relatively short-term compared to certain drugs; the relaxation obtained from exercising diminishes in about 4 hours, and anxiety levels return to normal in 24 hours.  Daily exercise is required if the person is suffering from chronic anxiety.  However, overworking could be stressful and bad for both body and mind.  

Tests have shown that a constant level of intensity of aerobic exercises enhances the brain’s capacity to process information the best. A study using soccer players showed that after running on a treadmill for 2- 45 minute time periods, their response time to a test involving real time soccer plays decreased with more time on the treadmill. In another separate study, female runners got better at solving simple math problems after a 20 minute run, and improved more after a 40-minute run. The mechanism behind the effect is not clear, but scholars believe that aerobic exercises act like stimulation drugs by releasing hormones and some chemicals such as adrenaline. However, working over the personal limit is not good for health.


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