Body size and countermeasure exercise: implications upon resource utilization during human space exploration missions with female astronauts

Abstract

Abstract Employing a methodology reported in a recent theoretical study on male astronauts, this study estimated the effects of body size and aerobic countermeasure (CM) exercise in a four-person, all-female crew composed of individuals drawn from a stature range (1.50- to 1.90-m) representative of current space agency requirements upon total energy expenditure (TEE), oxygen (O2) consumption, carbon dioxide (CO2) and metabolic heat (Hprod) production, and water requirements for hydration, during space exploration missions. Assuming geometric similarity across the stature range, estimates were derived using available female astronaut data (mean age: 40-y; BMI: 22.7-kg·m− 2; resting VO2 and VO2max: 3.3- and 40.5-mL·kg− 1·min− 1) on 30- and 1080-d missions, without and with, ISS-like countermeasure exercise (modelled as 2x30min aerobic exercise at 75% VO₂max, 6d·wk1). Where spaceflight-specific data/equations were not available, terrestrial equivalents were used. Body size alone increased 24-h TEE (+ 30%), O₂ consumption (+ 60%), CO₂ (+ 60%) and Hprod (+ 60%) production, and water requirements (+ 17%). With CM exercise, the increases were 25–31%, 29%, 32%, 38% and 17–25% across the stature range. Compared to the previous study of theoretical male astronauts, the effect of body size on TEE was markedly less in females, and, at equivalent statures, all parameter estimates were lower for females, with relative differences ranging from − 5% to -29%. When compared at the 50th percentile for stature for US females and males, these differences increased to -11% to -41% and translated to larger reductions in TEE, O2 and water requirements, and less CO2 and Hprod during 1080-d missions using CM exercise. Differences between female and male theoretical astronauts result from lower resting and exercising O2 requirements – based on available astronaut data of female astronauts who are lighter than male astronauts at equivalent statures, and having lower relative VO₂max values. These data, combined with the current move towards smaller diameter space habitat modules point to a number of potential advantages of all-female crews during future human space exploration missions.