Proof of the effect of testosterone on skeletal muscle

In spite of the widespread abuse of androgenic steroids by athletes and rec reational body-builders, the effects of these agents on athletic performanc e and physical function remain poorly understood. Experimentally induced an drogen deficiency is associated with a loss of fat-free mass; conversely, p hysiologic testosterone replacement of healthy, androgen-deficient men incr eases fat-free mass and muscle protein synthesis. Testosterone supplementat ion of HIV-infected men with low testosterone levels and of older men with normally low testosterone concentrations also increases muscle mass. Howeve r, we do not know whether physiologic testosterone replacement can improve physical function and health-related quality of life, and reduce the risk o f falls and disability in older men or those with chronic illness. Testoste rone increases maximal voluntary strength in a dose-dependent manner and th us might improve performance in power-lifting events. However, testosterone has not been shown to improve performance in endurance events. The mechani sms by which testosterone increases muscle mass are not known, but probably involve alterations in the expression of multiple muscle growth regulators .