You are talking with a friend who has recently started an exercise regimen, and

Question

You are talking with a friend who has recently started an exercise regimen, and they comment that they are planning to quit because they experience muscle soreness following their workouts. In your communication assignment for this week explain why this occurs. You should focus on the molecular mechanism of muscle contraction and how muscles become fatigued. You should also discuss the ways muscles adapt to changing activity levels at the molecular level as you encourage them to increase their fitness level.

Explanation / Answer

During the start of the workout, if the strenous excersice is performed then this leads to the pain and stiffness in the muscles which could be from hours to days. The main cause may be due to the lengthening excercise which leads to the small level of damage to the muscle fibres. But this could be completely adapted if the excersice regimen is strictly followed.

Molecular mechanism of muscle contractions:

Skeletal muscle is voluntary in nature as it control its action. This consist of bundle of muscle fibres. This single muscle fibre is long cylindrical cell and composed of myofibril. Muscle fibre also contain neuromuscular junction for receiving the signal regarding the muscle contraction.

Myofibril consist of contractile units called as sacromeres. Sacromeres run adjacent to each other and consist of thick and thin protein filaments. (straited appearence)

Thick protein filament called as myosin anchored in the centre of sacromere ie M line. Thin protein fialment called as actin anchored in the outer edges of sacromere ie Z line.

For the mechanism of muscle contraction ATP and calcium ion are involed in process. When signal regarding the muscle contraction is received atthe neuromuscular junction then the calcium ion is released from the sacroplasmic reticulum of mucle fibre. Actin filaments consist of two regulatory protein is troponin and tropomycin. When the muscle is in relax phase then this tropomycin is contract and leads to closing of binding site of calcium ion on the troppnin protein. As muscle contract, the released calcium ion binds to the troponin and this displces the tropomycin.

Myosin filament bind to the actin filament and producing the sliding action of actin forming cross bridges. This action take place when the ATP molecule binds to myosin and gets hydrolysed to aADP and inorganic phosphate. This release of energy causes the myosin filaments to pull the actin filaments close to the M line. This action leads to shortening of sacromere. Myosin filament remain attached with the actin filament untill the next ATP molecule attached itself to the myosin and get hydrolysed. This contraction of sacromere does not leads to the change in length of these filaments.

This contract results when the Z line draws close to the M line. The produce the response of muscle contraction.

Muscle become fatigued

When an excersice is vigorously proform for long period then their will be fatigued. This is due to the production of lactic acid in the muscles through anaerobic respiration. This fatigued produce due to i) shortage of fuel and ii) accumalation of substrate in muscle fibres (which interfere with the release of calcium ion and its binding)

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