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 The Pennsylvania State University Skeletal Muscle Growth Dynamics Arya Kermanshah March 19, 2014 Image: Skeletal muscle striations under a microscope. [Street Address] [City], [State] [Postal Code] Phone: [Your Phone] Fax: [Your Fax] E-­‐Mail: [Your E-­‐Mail] Web: [Web Address] Skeletal Muscle Growth Dynamics 1 Skeletal Muscles Movements There are over 600 different muscles in the human body. Muscles have a large role in every one of our system functions such as the the cardiovascular system, and even the digestive system. Skeletal muscles are attached to our skeletal system and are responsible for all of our external movements. All of these movements are controlled by the central nervous system (CNS). The CNS system controls bodily functions through a series of action potentials that pass through a chain of neurons all the way to the neuromuscular junction. This causes a specific motion of the body. This process is triggered by resistance training and is described below in four distinct stages : Muscle Activation, Muscle Contraction, Recharging, and Relaxation. Stage 1 -­‐ Muscle Activation: The motor nerve sparks an action potential, an impulse sent from the brain, to the neuromuscular junction. This stimulates the release of calcium from the sarcoplasmic reticulum into the muscle cells. I.
Sarcoplasmic Reticulum : The specialized smooth endoplasmic reticulum found in striated muscle fibers. Its function is to store and release calcium ions. Stage 2 – Muscle Contraction: The calcium that was released from the sarcoplasmic reticulum binds with troponin, a muscular protein. This allows for the binding of Actin and Myosin. Actin and myosin contract using ATP. I.
Actin : The « thin » protein filaments that make up a sarcomere. Skeletal Muscle Growth Dynamics 2 II.
Myosin : The « thick » protein filaments that make up a sarcomere. III.
Sarcomere : The basic functioning unit of a muscle comprised of actin and myosin filaments. Sarcomeres are responsible for the striated appearance of skeletal muscle systems. When actin and myosin contract together, all sarcomeres in the muscle system contract and cause the entire organ to contract. The sarcomere is also referred to as the A-­‐Band based on its anisotropic nature. The I-­‐band is named after its isotropic nature as it keeps the A-­‐bands separated. Stage 3 – Recharging: ATP, the energy compound that fuels all cells, runs through a resynthesizing process that allows for actin and myosin to remain in a binded state. Stage 4 – Relaxation: The muscle will experience relaxation when stimulation of the nerve ends. At this stage calcium is pumped back into the sarcoplasmic reticulum which breaks the link between actin and myosin. This causes actin and myosin to return to their unbound states and for the muscle to relax. Another way this can happen is through muscle failure which happens when ATP is no longer available. ATP availability can increase and decrease based on an individual’s level of fitness and diet. See Resistance Training for more information about muscular endurance. Resistance Training Muscle growth is directly related to resistance training. There are two different target exercises that resistance trainers take into consideration, strength training and endurance training. In general, strength training exercises include low repetitions but involve heavier weights. Endurance training exercises include high repetitions with lighter weights. Both of these training methods share the same goal of increasing blood flow in their bodies. Increased blood flow leads to a higher level of stamina which allows for longer periods of strenuous activities. Strength and Endurance Training: Combined, these two training methods are responsible for individual cell elongation and growth which causes the muscle to grow as a whole. Most growth occurs while the muscle is in relaxation mode . After a completed workout, muscles are stretched and torn. To prevent injury, your muscles need time to relax and repair which is why rest days are important. I.
Strength Training : Through shorter high-­‐intensity workouts, strength training causes blood to pump through the capillaries in the skeletal muscle which delivers oxygen to the cells containing the sarcoplasmic reticulum. New capillaries are formed when blood flow cannot be contained by the capillaries that are already present. This results in even more oxygen and production of ATP. The more ATP that is available, the longer the muscle can remain contracted, and the longer the individual can remain in exercise. ATP is generated in the mitochondrial organelles found in all animal cells. II.
Endurance Training : The longer the time that a muscle is forced to contract and relax, the higher the demand for ATP is. Due to the limited number of mitochondrial organelles present to begin with, more mitochondria must be formed to accomodate all of the extra oxygen that is pumped into the system. In this way, endurance training allows for individuals to exert themselves for longer periods of time. Muscle Growth Limitations There are many factors that permit and limit individuals from achieving their full muscle potential. An individual’s overall muscular potential is determined by a protein called myostatin. Your genes are directly responsible for myostatin production ability. The more Skeletal Muscle Growth Dynamics 3 myostatin your body can produce, the less massive your muscles can become. Body builders who achieve a « hulk-size » have very little of myostatin in their bodies. I.
Factors Preventing individuals from achieving full muscle potential. a.
High myostatin levels. b.
Poor exercise form – This leads to muscle damage. To prevent further injury ,the individual must take a break from exercising. This will give the muscles sufficient time and energy to repair themselves. c.
Low protein diet – With a low protein diet, muscles will not have the necessary nitrogen levels and enzymes to repair broken tissue and to grow. d.
Lack of sleep -­‐ Sleep is essential for the body to be able to relax and focus on reparation. Myostatin GDF-­‐8 is the gene responsible for the production of myostatin. Myostatin production is a component of your Basal Metabolic Rate (BMR), also known as your metabolism. I.
BMR : The body’s metabolism is variable based on your genes and your daily activities. BMR is the driving force that determines the exact energy allocation your body needs for daily activities. a.
Gender – Men have a higher BMR than women. b.
Age – As individuals grow older, their BMR decreases. c.
Diet – Eating a diet comprised of more natural foods allows the body to allocate less energy to break those foods down, but more energy to absorb the essential nutrients. d.
Activities – Physical activities increase muscle mass and heat production, which increases BMR. Based on the individual’s daily activities, food intake, and genetic code, they may experience either hypertrophy, hypotrophy, or isotrophy. Hypertrophy-­‐ The increase of a muscle due to the enlargment of its component cells. Observed in body builders. Hypotrophy-­‐ The degradabon of a muscle due to the loss and shrinkage of cells. Observed in moble organizms living sessile lives. Isoptrophy-­‐ Neither degradabon, nor growth of muscle cells occurs. Essenbally due to a regular lifestyle. Muscle Growth Supplements: Scientists have developed protein combinations, and supplemental pills that promote muscle growth and repair. Myostatin inhibitors have also been developed. None of these supplements have actually been proven to have as great of an impact as advertised. The most reliable method of muscle growth is to exercise regularly and keep a healthy diet. Skeletal Muscle Growth Dynamics 4 Work Cited
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