The Study On Water Loss And Energy Expenditure Of Simulated Space Activities

Objective: To study the water loss and energy expenditure of different simulated space activities and to study the relationship of metabolic rate(MR) and whole-body sweat rate(WBSR) to predict MR from WBSR.Methods: MR was measured in a whole-room indirect calorimeter and body weight(BW) was measured by a precision body scale. Twenty two male subjects(age 25.0±3.8, height 1.71±0.02 m, weight 65.7±4.7 kg, body fat percentage 14.9±6.5 %) stayed in the whole-room indirect calorimeter of Capital Medical University, simulated different space activities and stayed for 24 hours doing those activities while every minute MR and total energy expenditure(TEE) were recorded. Meantime, BW was measured before and after every designed activity to calculate WBSR and daily water loss. Total energy and water requirements of astronauts were provided, correlations between MR and WBSR of different activities was analyzed and the predicted equations were developed.Results: Physical activity level(PAL) was 1.73±0.13, TEE was 2772.5±201.3 kcal, daily water loss was 3307.8±483.3 g, MR and WBSR ranged from 1.76 to 6.90 kcal/min and from 0.70 to 7.14 g/min, respectively. MR per unit body weight and MR per unit fat free mass(FFM) ranged from 0.027 to 0.105 kcal/(min·kg) and from 0.032 to 0.124 kcal/(min·kg), respectively. WBSR per unit body weight, WBSR per unit fat free mass and WBSR per unit body surface area ranged from 0.017 to 0.109 g/(min·kg), from 0.013 to 0.127 g/(min·kg) and from 0.412 to 4.183 g/(min·m2). A linear correlation between MR and WBSR was found in activities with relatively high intensity(p<0.05). MR was linearly predicted by WBSR in continuous treadmill exercise with 55%VO2max: MR=0.3339×WBSR +3.6209, R2=0.92, RMSE=0.36.Conclusion: The study presents a novel method using whole-body sweat rate to predict metabolic rate in different activities. Total energy and water requirements for simulated space life activities of were calculated in this study, the data roughly covers the normal range of physiological parameters of Chinese astronauts including age, height, body weight, body fat percentage, maximum oxygen consumption and basal energy expenditure.