Relatively minor influence of individual characteristics on critical wet-bulb globe temperature (WBGT) limits during light activity 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 (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.

Temperature–Humidity-Dependent Wind Effects on Physiological Heat Strain of Moderately Exercising Individuals Reproduced by the Universal Thermal Climate Index (UTCI)

“…The selected study population of young, healthy, and fit males certainly limits the generalizability of our findings, though recent research suggests only minimal influences of individual factors on the heat stress assessment under moderate activity levels [ 61 ], as applied in our study. As another limitation, the responses of semi-nude participants ( I cl = 0.1 clo) might differ from the effects with clothed humans, e.g., as assumed by the UTCI with clothing insulation not falling below I cl = 0.3 clo [ 34 ].…”

Relative Influence of Meteorological Variables of Human Thermal Stress in Peninsular Malaysia

“…As a result of the amplification of heat stress by climate change, there is an increased risk of heat-related ailments and deaths, especially among vulnerable populations such as the elderly, infants, and those with preexisting health conditions [4,[14][15][16]. Therefore, it is essential to address the effects of thermal stress on humans caused by climate change [17,18].…”

“…Heat Index (HI) or "Feels Like" Temperature, Wet Bulb Globe Temperature (WBGT), Humidex, Apparent Temperature (AT), Predicted Heat Strain (PHS), Universal Thermal Climate Index (UTCI), and Discomfort Index (DI) are some commonly used heat stress indices [19][20][21][22]. The information provided by these indices [19] assists individuals, communities, and industries in recognizing and mitigating the hazards associated with heat stress [18]. WBGT stands out among these indices due to its exhaustive evaluation of heat stress in occupational and outdoor environments [3,[23][24][25].…”