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 spaceflight 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 spaceflight 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 five 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 significantly 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 significant differences in BMR (pre-bed 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 findings highlight the importance of energy balance for long-duration crewmembers completing a high-intensity exercise program with multiple exercise sessions daily.

Adaptation in locomotor stability, cognition, and metabolic cost during sensory discordance.

BACKGROUND: Locomotor instability may affect planetary extravehicular activities during the initial adaptation to the new gravitational environment. The goal of this study was to quantify the locomotor, cognitive, and metabolic effects of exposure to a discordant sensory environment. METHODS: A treadmill mounted on a 6-degree-of-freedom motion base was used to present 15 healthy subjects with a destabilizing support surface while they walked. Dependent measures of locomotor stability, cognitive load, and metabolic cost were stride frequency (SF), reaction time (RT), and the volume of oxygen consumed (Vo2), respectively. Subjects completed an 8-min baseline walk followed by 20 min of walking with a continuous, sinusoidal, laterally oscillating support-surface perturbation. Data for minutes 1, 7, 13, and 20 of the support-surface perturbation period were compared with the baseline. RESULTS: SF, RT, and Vo2 were significantly greater during support-surface motion than during the baseline walking condition and showed a trend toward recovery to baseline levels during the perturbation period. Results demonstrated that adaptation to walking in a discordant sensory environment has quantifiable and significant costs in SF, RT, and Vo2 as shown by mean increases of 9%, 20%, and 4%, respectively, collected during the first minute of exposure. By the fourth minute of exposure, mean Vo2 consumption had increased to 20% over its baseline. DISCUSSION: We believe that preflight sensorimotor adaptation training paradigms will impart gains in stability and the ability to multitask, and might increase productive mission time by extending work time in extravehicular activity suits where metabolic expenditure is a limiting factor.

Metabolic consequences of garments worn to protect against post-spaceflight orthostatic intolerance.

INTRODUCTION: Astronauts have worn an inflatable antigravity suit (AGS) during Space Shuttle re-entry and landing to protect against hypotension and syncope, but ambulation with an inflated AGS requires significant effort and may prevent successful completion of an unaided emergency egress from the vehicle. NASA is considering the use of alternative garments to provide protection against post-spaceflight orthostatic intolerance. The purpose of this study was to compare the metabolic cost of walking in NASA's current AGS with that of walking in a commercially available elastic compression garment (thigh-high stockings), a candidate garment for use after exploration missions. METHODS: There were 10 volunteers (5 men, 5 women) who walked on a treadmill at 5.6 km x h(-1) for 5 min, a simulation of unaided egress previously used in our laboratory, in 3 different conditions presented in random order: wearing exercise clothes, wearing elastic compression garments, and wearing the AGS. Oxygen consumption (Vo2), carbon dioxide production (Vco2), and ventilation (V(E)) were compared using repeated-measures ANOVA and Tukey's Honestly Significant Difference test. RESULTS: Vo2 while wearing the AGS was 12% greater than when wearing the elastic compression garments and 15% greater than while wearing exercise clothes. There were no differences between the elastic compression garments and exercise clothes only conditions. Vco2 and VE also were greater while walking in the AGS than walking in the elastic compression garments or exercise clothes. CONCLUSIONS: Wearing elastic compression garments as a countermeasure to post-spaceflight orthostatic intolerance may not impair unaided egress from a space vehicle.