User: Jim Fitch decided that his physique left much to be desired, so he joined a local health club and began to "pump iron" three times weekly. After three months of training, during which he was able to lift increasingly heavier weights, he noticed that his arm and chest muscles were substantially larger. Explain the structural and functional basis of these changes.

Weegy: Weight training provides us with exercises that take skeletal muscles through their normal range of motion. [ So, structurally, when a muscle is worked against a resistance it is not accustomed to, it will begin to adapt to the resistance, and neuromuscular facilitation will also occur. There are two theories I am familiar with that deal with muscular growth. The first is hypertrophy, where individual muscle fibers become bigger, therefore making the muscle bigger. The other theory is hyperplasia, which is the dividing of a muscle fiber. When thousands of muscle fibers divide, this will also make the entire muscle larger. Because Jim challenged the muscle by increasing the weights gradually, the muscle was able to adapt gradually. Overtraining must not have occured here. He allowed the muscle time to recover before working it again. I hope this helps you. ]
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