Some of these skeletal muscle fibers here show atrophy, compared to normal fibers. The number of cells is the same as before the atrophy occurred, but the size of some fibers is reduced. This is a response to injury by "downsizing" to conserve the cell. In this case, innervation to the small, atrophic fibers was lost. (This is a trichrome stain.)

Question: What is the most common cause for muscle atrophy?

AnswerThe most common cause is disuse. In healthy people this occurs from lack of exercise. Ill persons who are bedridden can have considerable muscle atrophy.