Mechanisms and strategies to counter muscle atrophy.

Skeletal muscle size is modulated by a number of factors, including muscle load, utilization, and regenerative capacity. Surprisingly, actions that can promote muscle growth do not necessarily prevent the loss of muscle mass, or atrophy. This suggests that divergent mechanisms are important for the maintenance of muscle mass in different contexts. In acute atrophy, muscles rapidly lose mass when load is lacking, and this response seems to involve active elimination of myonuclei. In contrast, chronic atrophy, such as loss of muscle mass related to aging, is associated with impairments in muscle repair. In this review, two contexts in which muscle mass is lost are explored to determine if similar processes are involved.