Relative influence of individual characteristics on critical WBGT limits in young adults (PSU HEAT Project)

Abstract

Critical environmental limits are temperature-humidity thresholds above which heat balance cannot be maintained for a given metabolic heat production. This study examined the association between individual characteristics [sex, body surface area (A D ), aerobic capacity (V̇O 2max ; L∙min-1), and body mass (m b )] and critical environmental limits in young adults. Forty-four (20 M/24 F; 23±4 yr) subjects were exposed to progressive heat stress in an environmental chamber at two low net metabolic rates (M net ); minimal activity (MinAct; M net = 160±35 W) and light ambulation (LightAmb; M net = 259±54 W). In 2 hot-dry (HD; <25% rh) environments, ambient water vapor pressure (P a = 12 or 16 mmHg) was held constant and dry-bulb temperature (T db ) was systematically increased. In 2 warm-humid (WH; >50% rh) environments, T db was held constant at 34 or 36 °C and P a was systematically increased. The critical wet-bulb globe temperature (WBGT crit ) was determined for each condition. There were no sex differences in WBGT crit for any condition ( p ≥ 0.21). During MinAct, only m b was retained in a backward linear regression model explaining the variance in WBGT crit in WH (R 2adj = 0.08, p < 0.001), whereas m b and V̇O 2max were retained for HD environments (R 2adj = 0.09, p < 0.001). During LightAmb, m b and A D were retained in the model for both WH (R 2adj = 0.46, p < 0.001) and HD environments (R 2adj = 0.22; p < 0.001). These data demonstrate the relative importance of individual characteristics on WBGTcrit during low-intensity weight-bearing (LightAmb) and non-weight-bearing (MinAct) activity in extreme thermal environments. This work was supported by NIH R01 AG067471. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.