Effects of 10 days of bedrest on body composition and the rate of muscle protein synthesis in older men and women

Abstract

The effects of bed rest are well described in younger subjects but have not been evaluated in older adults. The objective of this study was to examine the effects of 10 days of bed rest on body composition changes and muscle protein synthesis in healthy older people. Eight subjects (68 ± 5 yo, M/F: 2/6) remained in bed, except for toileting, for 10 consecutive days. All subjects consumed a eucaloric diet providing 0.8 g protein·kg−1·d−1. Body composition (DEXA), and muscle protein synthesis (24-hr infusion of 13C6-phenylalanine) were assessed before and immediately after bed rest. On average, there was a 7% loss of lower extremity lean tissue in these subjects (14454 g to 13511 g, p<0.05), and the fractional muscle protein synthetic rate declined 44% (n=4, 0.086 %·hr−1 to 0.048 %·hr−1, p<0.05). These results indicate that there is a significant loss of muscle, with a more pronounced decline in muscle protein synthesis as a result of 10 days of bed rest. This loss of muscle in these older people after 10 days is greater than that seen in previous studies in young subjects after 28 days of bed rest. These data are of particular significance given the number of older adults that experience prolonged bed rest during hospitalization or institutionalization. Prophylactic measures to prevent loss of skeletal muscle in elderly people during prolonged periods of inactivity should be given a high priority. NIH PO1 AG023591, M01 RR14288