There are many unanswered questions regarding maintenance of muscle and muscle function in old age. The Laboratory of Epidemiology, Demography and Biometry has organized several large population studies targeted to understanding, on a population level, factors that influence the relationship between body composition, particularly muscle, and strength over time. These studies have been successful in allowing identification of new hypotheses regarding factors that might influence the course of disability, including the observation that fat infiltrates into muscle, both in obesity and in disuse. Further population work has shown that the amount of muscle fat may vary by gender and race and that muscle fat increases with age, but at a later age than visceral fat. However, little is known about how fat actually influences muscle. The purpose of this professional services contract is to obtain computerized tomography scans of the muscle, bone and fat in the arms and leg at three points in time in a clinical intervention: at the time of maximum muscle hypertrophy secondary to intervention, at the end of a period of deconditioning, and at the end of a period of intensive reconditioning. Dr. Dennis Taaffe of the University of Queensland,Brisbane, Australia, and his colleagues have established a protocol to test the hypothesis that a high-velocity progressive resistance training will increase measures of muscle function to a greater extent than a conventional progressive resistance training protocol. The protocol established contains extensive measurements of muscle response to interventions as is indicated below: dynamic muscle strength using the one repetition maximum (1RM) method, muscle endurance at 70% of 1RM, peak and average muscle power as well as velocity of movement, and a battery of physical performance tests (floor rise to standing, stair climb, 6-m backwards walk, 6-m usual and fast walk, chair rise, 400-m walk, and functional reach). Dr. Harris's project adds a CT imaging protocol to Dr. Taeffe's study for 20 subjects at three time points during the course of the study. Through imaging of muscle mass we will quantify muscle hypertrophy and assess the extent to which the exercise interventions might influence muscle attenuation and muscle fat.