Effects of growth hormone on skeletal muscle.
Human growth hormone (GH) is widely abused as a performance-enhancing anabolic drug by athletes and bodybuilders. However, the effects of GH on skeletal muscle mass, strength and fibre composition remain unclear. We therefore summarize in the following the current knowledge on the physiological role of GH in the regulation of skeletal muscle growth and function and evaluate its potential therapeutic potency as a muscle anabolic hormone. In states of GH deficiency, reduced muscle mass and strength are characteristic findings which can be reversed successfully by the supplementation of GH. In contrast, the currently available data suggest that GH administration alone or in combination with strength exercise has little, if any, effect on muscle volume, strength and fibre composition in non-GH-deficient healthy young individuals. This assumption is supported by the lack of evidence for a significant performance-enhancing effect of GH in athletes. However, further studies will be necessary to define patient populations which might benefit from GH treatment like frail elderly individuals in whom a GH-induced change into a more youthful muscle fibre composition has been reported.