ENERGY-EXPENDITURE DURING ANTIORTHOSTATIC BED REST (SIMULATED MICROGRAVITY)

Few studies have addressed the interaction between energy balance and lean body mass in healthy subjects during spaceflight or its simulatio ns. We used doubly labeled water to measure total energy expenditure ( TEE) in nine healthy adult men during two 7-day periods, once before a nd once during a 10-day head-down bed-rest period. Mean TEE was 21% le ss during than before bed rest; however, neither basal (BEE) nor resti ng (REE) energy expenditures changed, implying that the lesser TEE res ulted from a reduction in physical activity. During the bed-rest perio d, energy intake was 563 +/- 280 kcal/day higher than TEE (P < 0.05) b ut body weight, fluid balance, BEE, and REE did not change relative to before bed rest. However, the small but statistically significant inc rease in body fat (0.44 +/- 0.67 kg, P < 0.05) during the bed-rest per iod suggests that body weight alone does not accurately reflect change s in energy balance during antiorthostatic bed rest.