Study of Inactivity on Metabolism of Elderly Muscles

Skeletal muscle mass declines with inactivity (casting is a good example) and increases with activity (such as weightlifting). Whether muscle mass increases or decreases, is determined by whether more new proteins within muscle are made than are broken down. The investigators know that feeding protein increases the synthesis of new proteins but that the response of older muscles to protein feeding is blunted compared with the young. This resistance of the elderly to muscle building stimuli may be the primary reason that muscle mass is lost in aging. The investigators also know that periods of muscle disuse such as casting result in a person's muscle shrinking due, the investigators believe, to a lower rate of synthesis of new muscle proteins. Age-related muscle loss begins around 50 years old and proceeds at approximately 1% for every year after. Elderly persons would likely fare well with advancing age if their muscle loss were simply linear; however, a rate of muscle loss of 1% annually is a 'population view' and does not represent what occurs during short periods of muscle disuse (i.e. during hospitalization or illness), which occur with increasing frequency in elderly persons. During periods of disuse, the resistance of elderly muscles to protein nutrition may be worsened. The investigators will measure how quickly new proteins are made at rest and after protein feeding in elderly men, before and after a 14 day period of reduced activity brought on by having people reduce their daily step count.