LAUSR

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 (AD), aerobic capacity (V̇O2max), and body mass (mb)] and critical environmental limits in young adults at low metabolic rates. Forty-four (20 M/24 F; 23±4 yrs) subjects were exposed to progressive heat stress in an environmental chamber at two low net metabolic rates (Mnet); minimal activity (MinAct; Mnet = ~160 W) and light ambulation (LightAmb; Mnet = ~260 W). In 2 hot-dry (HD; ≤25% rh) environments, ambient water vapor pressure (Pa = 12 or 16 mmHg) was held constant and dry-bulb temperature (Tdb) was systematically increased. In 2 warm-humid (WH; ≥50% rh) environments, Tdb was held constant at 34 or 36 °C and Pa was systematically increased. The critical wet-bulb globe temperature (WBGTcrit) was determined for each condition. During MinAct, after entry of Mnet into the forward stepwise linear regression model, no individual characteristics were entered into the model for WH (R2adj = 0.01, p = 0.27) or HD environments (R2adj = -0.01, p = 0.44). During LightAmb, only mb was entered into the model for WH environments (R2adj = 0.44, p < 0.001), whereas only V̇O2max was entered for HD environments (R2adj = 0.22; p = 0.002). These data demonstrate negligible importance of individual characteristics on WBGTcrit during low-intensity non-weight-bearing (MinAct) activity with a modest impact of mb and V̇O2max during weight-bearing (LightAmb) activity in extreme thermal environments.