Body Building: Health, Medicine, Nursing Essay

Body Building
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Body Building
According to the sliding filament theory, the myofibril contracts when the myosin and actin filaments slide over each other. The chemical bonds and the receptor sites attract each other on the myofilament allowing contraction to occur until fatigue occurs. The strength by which muscles contract depends on muscle fibers—the more the muscle fibers, the stronger the contraction.
The size principle of motor unit recruitment states that fibers with higher reliability levels are recruited first, while fibers with low levels of reliability are recruited last. On the one hand, highly reliable fibers are slow-twitch filaments with the least motor units. On the other hand, less reliable fibers are fast-twitch filaments with the most motor units. Slow-twitch and fast-twitch muscle fibers can be categorized as Type I and Type II, respectively. Type I fibers are small and endurance based. However, type II fibers are only recruited when one uses more than 25% of their strength.
All or none theory states that every myofibril is fundamental to its functioning. It always contracts fully and responds with an all or none reaction. Myofibrils are essential to muscle contraction. When nerves carry impulses of sufficient magnitude to the muscle cells, the myofibrils can only respond by contracting or shortening. Muscle fibers, including the myofibrils, respond to n...