Background. Extravehicular activity poses several dangers to astronauts. A major concern is the regulation of core temperature and thermal comfort in the context of an impermeable EMU microclimate and elevated energy expenditure rates for prolonged periods. Purpose. To identify the optimal features of each of three LCGs (MACS-Delphi, Russian Orlan, NASA LCVG) for maintaining core temperature and thermal comfort during exercise in mild (24 °C) and hot (35 °C) conditions. Methods. Four male and two female participants (aged 22-46 years) performed 10 trials (each with five 20-minute exercise stages and two rest stages) to account for all garment configurations (with/without hood) and temperature regimes. Metabolic (VO2, Ve, RER), temperature (core, skin), cardiovascular (HR, SBP, DBP, SaO2), local sweat rate, and skin wetness data were collected and analyzed during stages five (moderate exercise) and seven (rest). Whole body sweat rate and water flow parameters were collected pre- and post-trial. Results. Significant differences (p ≤ 0.05) between garments were found for: skin temperature, HR, SBP, local and whole body sweat rate, and water flow rate. Discussion . There were several significant, yet few consistent, findings between the garments. Use of a cooling hood had no discernable effect. Amount of tubing coverage was related to whole body sweat rate while flow rate affected skin temperatures and local sweat rate. Conclusion. All three garments were similar in terms of regulating core temperature in a safe range (though not to the NASA standard of 37.2 °C) during physical exertion in moderate and hot environments. Future research is needed to identify the roles of adding a cooling hood and/or ventilation system to LCGs in addition to determining optimal water temperature, flow rate, tubing arrangement, and ergonomic design.
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