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 lifted...

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 lifted increasingly heavier weights, he noticed that his arm and chest muscles were substantially larger. Explain the structural and functional basis of these changes.