The metabolic cost of an integrated exercise program performed during 14 days of bed rest

Background: Exercise countermeasures designed to mitigate muscle atrophy during long-duration spacefl ight may not be as effective if crewmembers are in negative energy balance (energy output > energy input). This study determined the energy cost of supine exercise (resistance, interval, aerobic) during the spacefl ight analogue of bed rest. Methods: Nine subjects (eight men and one woman; 34.5 ±8.2 yr) completed 14 d of bed rest and concomitant exercise countermeasures. Body mass and basal metabolic rate (BMR) were assessed before and during bed rest. Exercise energy expenditure was measured during and immediately after [excess post-exercise oxygen consumption (EPOC)] each of fi ve different exercise protocols (30-s, 2-min, and 4-min intervals, continuous aerobic, and a variety of resistance exercises) during bed rest. Results: On days when resistance and continuous aerobic exercise were performed daily, energy expenditure was signifi cantly greater (2879 ±280 kcal) than 2-min (2390 ±237 kcal), 30-s (2501 ±264 kcal), or 4-min (2546 ±264 kcal) exercise. There were no signifi cant differences in BMR (prebed rest: 1649 ±216 kcal; week 1: 1632 ±174 kcal; week 2: 1657 ±176 kcal) or body mass (pre-bed rest: 75.2 ±10.1 kg; post-bed rest: 75.2 ±9.6 kg). Discussion: These fi ndings highlight the importance of energy balance for long-duration crewmembers completing a high-intensity exercise program with multiple exercise sessions daily.