Sarcopenia in old age is the loss of skeletal muscle mass, quality, and strength. This proposal argues that little is known about the mechanisms of age-related sarcopenia, the rate at which it develops, if specific muscle groups are involved, and if gender differences exist. Moreover, the applicant points out that the limited information available derives from studies of Caucasians, and that no major studies have specifically examined skeletal muscle changes in elderly African-Americans. The applicant's preliminary data from a large (n=284) relatively young cross-sectional cohort indicates that, after adjusting for stature and body weight, men have more appendicular muscle than women, but both the absolute and relative rates of muscle loss with age are greater in men. Furthermore, in a longitudinally monitored subgroup from the same study (n=50, 38 female, baseline age 70 years, followup at 74) a two-fold greater rate of muscle loss was observed in these more elderly subjects compared to the average in younger, cross-sectional study, and the loss rate was higher in African-Americans. The proposed study hopes to confirm these preliminary findings by examining the rate of muscle and strength loss in a cohort of 80 community-dwelling African-American subjects (>70 years old) over a five year period. In addition, the study will test the hypothesis that accelerated muscle loss is associated with reductions in physical activity, as measured by combined respiratory chamber indirect calorimetry and doubly-labeled water loss. Finally, the study will examine associations between muscle loss vs. hormonal status and physical function/performance tests. The project will yield data which is not presently available in this subject population.