With increasing age, there occurs a decline in the capacity of many tissues to synthesize proteins. Most notable is the loss of skeletal muscle mass that accompanies aging and the concommitant reduction in muscle strength that leaves many elderly individuals disabled or unable to function independently. The potential benefits of heavy resistance exercise training and/or growth hormone (GH) administration to elderly individuals to retard age-related muscle atrophy and the reduction in bone mass have not been studied systematically. With the availability of biosynthetic human GH, it is now possible to safely and effectively study the anabolic effects of GH administration on whole body and skeletal muscle protein kinetics and bone metabolism in elderly individuals engaged in heavy resistance exercise training. Therefore, the purpose of this project is to determine the effects of GH administration and heavy exercise training on the following measures made in 65-75 year old males prior to and following each treatment. The specific aims are to observe the changes in protein synthesis and breakdown that occur at the whole body level and within muscle tissue of elderly males receiving GH therapy and/or heavy resistance exercise by (1) measuring whole body nitrogen (N) turnover, protein synthesis and breakdown by determining the urinary excretion of total 15N, 15NH3 and 15N-urea following oral administration of 15N glycine; (2) measuring whole body leucine and protein kinetics from the dilution of a primed, continuous infusion of L-(1-13C) leucine by determining the plasma 1-13C leucine enrichment, plasma 1-13C alpha-ketoisocaproate enrichment, expired 13CO2 enrichment, and CO2 production rate; (3) measuring the in vivo rate of skeletal muscle protein synthesis by determining the rate of incorporation of L-(1-13C) leucine into skeletal muscle protein; (4) measuring skeletal muscle tissue levels of mRNA for insulin-like growth factor-1; (5) and measure improvement in muscular strength using an isokinetic dynamometer.