Abstract

To determine the cause of the body weight loss during bed rest (BR), fluid balance and anthropometric measurements were taken from seven men (19-21 yr) during three 2-wk BR periods which were separated by 3-wk ambulatory recovery periods. Caloric intake was 3,073 Plus-Minus 155 (SD) kcal/day. During two of the three BR periods they performed supine isotonic exercise at 68 of VO2 max on the ergometer for 1 h/day; or supine isometric exercise at 21 of maximal leg extension force for 1 min followed by a 1-min rest for 1 h/day. No prescribed exercise was given during the other BR period. During BR, body weight decreased slightly with no exercise (-0.43 kg, NS), but decreased significantly (P<0.05) by - 0.91 kg with isometric and by - 1.77 kg with isotonic exercise About one-third of the weight reduction with isotonic exercise was due to fat loss (- 0.69 kg) and, the remainder, to loss of lean body mass (- 0.98 kg). It is concluded that the reduction in body weight during bed rest has two major components. First, a loss of lean body mass caused by assumption of the horizontal body position that is independent of the metabolic rate. Second, a loss of body fat content that is proportional to the metabolic rate. Verf.-Referat