This research will examine changes in skeletal muscle and bone due to simulated bedrest in young and old rats. The primary hypothesis to be examined is that simulated bedrest is more detrimental to skeletal muscle and bone in old than in young rats. We will examine both changes in muscle contractile function and possible histochemical and biochemical correlates of muscle function following bedrest. We will also evaluate changes in bone strength in conjunction with analysis of bone mineral content and potential histological alterations. Various treatments, all of which may be used clinically to attempt to ameliorate the detrimental effects of bedrest, will be employed in young and old animals. Treatment outcomes are expected to provide guidance for the clinician on strategies that may be employed readily for patients on required bedrest. the applicant has extensive experience with treating older adults following periods of prolonged bedrest. Her clinical observations led her to begin exploring some of the reasons for functional changes due to bedrest using an animal model which allows for more in depth evaluation of these effects. In addition, these studies should enhance understanding of the effects of bedrest and rehabilitation within an aging context.