Background: The loss of skeletal muscle mass that occurs with aging, chronic disease or acute injury is clinically important in the health of humans. The mechanisms relating to the synthesis and breakdown of skeletal muscle are now being intensely investigated. Current studies and possible mechanisms for skeletal muscle protein synthesis and degradation will be reviewed with a specific focus on growth hormone and testosterone. Conclusions:Investigation of the mechanisms of action of growth hormone and testosterone in skeletal muscle will likely lead to new therapies to prevent skeletal muscle loss and new awareness of the importance of skeletal muscle in health and disease.

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