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, especially with regard to gene expression. The purpose of this project is to establish a study to obtain fat from the muscles of the back.