Margo recently began working out and jogs three times a week. After her jog, she is breathless, and her muscles ache. From your understanding of muscle physiology, describe what has happened inside of Margo’s skeletal muscle cells. How do Margo’s muscles recover from this? If Margo continues to exercise, what changes would you expect to occur in her muscles?

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Muscle fibers get their ability to contract from adenosine triphosphate, ATP, a molecule that when broken down transfers a powerful, though remarkably short-lived, burst of energy to the surrounding cells.

Sustained voluntary movement requires a great deal of energy, but very little ATP is available for immediate use. As soon as a person begins exercising, their body must begin to convert stored compounds into ATP. Initially, the body uses phosphocreatine, a molecule that works in conjunction with ADP to store small amounts of the reactants required to produce ATP. Phosphocreatine metabolism can supply the muscles with about ten more seconds’ worth of energy before it too is depleted. Next, the body draws upon its glucose and glycogen stores to produce ATP. This reaction is more complicated than phosphocreatine metabolism, but it will provide about ninety seconds’ worth of energy to the muscle fibers. It will also produce the aching, burning sensation...

(The entire section contains 485 words.)

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