Men and women undergo a progressive reduction in lean muscle mass (sarcopenia) with advancing age regardless of their level of physical activity. A 12-yr longitudinal study in healthy sedentary older men showed a correlation between loss of muscle cross-sectional area and muscle strength of the thigh, quadriceps, and flexor muscles. Once weakened, older individuals are prone to falls that prevent independent living and diminish the quality of life. There is a need to develop therapies to counteract losses in skeletal muscle strength with aging. Studies show that exercise and testosterone administration increase skeletal muscle mass and strength in older men. However, the increase in muscle strength by testosterone in older men has not been consistent in all studies. Androgens increase muscle mass by either increasing muscle protein synthesis or inhibiting muscle protein breakdown. This proposal will investigate the hypothesis that cyclic testosterone administration (monthly on/off cycles) will preferentially increase muscle protein synthesis and result in a consistent and greater improvement in muscle strength than continuous testosterone administration.