Muscle Atrophy

Muscle atrophy refers to the wasting away or decrease in the size of muscle tissue from lack of use or through immobilization. It is the counterpart to hypertrophy: where training enlarges fibers, disuse and immobilization shrink them. A related point from the source's weight-control discussion is that muscles that are not used will simply experience atrophy (get smaller) — and fat tissue cannot turn into muscle, nor muscle into fat; unused muscle may merely be replaced by fat if a person consumes more calories than expended.

• Atrophy = wasting away / decrease in size of muscle tissue.
• Caused by lack of use or immobilization.
• Opposite of hypertrophy.
• Unused muscle simply gets smaller (and may be replaced by fat if calories exceed expenditure).

• muscle-hypertrophy — the opposite adaptation (growth).
• muscle-tone — firmness lost with disuse.
• recovery-physiology — over-rest/lay-off leads to loss of contractile force.
• reversibility-disuse — "use it or lose it" training principle.