Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania.
Center for Healthy Aging, College of Health and Human Development, The Pennsylvania State University, University Park, Pennsylvania.
J Appl Physiol (1985). 2022 Oct 1;133(4):1011-1018. doi: 10.1152/japplphysiol.00388.2022. Epub 2022 Sep 1.
With global warming, much attention has been paid to the upper limits of human adaptability. However, the time to reach a generally accepted core temperature criterion (40.2°C) associated with heat-related illness above (uncompensable heat stress) and just below (compensable heat stress) the upper limits for heat balance remains unclear. Forty-eight (22 men/26 women; 23 ± 4 yr) subjects were exposed to progressive heat stress in an environmental chamber during minimal activity (MinAct, 159 ± 34 W) and light ambulation (LightAmb, 260 ± 55 W) in warm-humid (WH; ∼35°C, >60% RH) and hot-dry (HD; 43°C-48°C, <25% RH) environments until heat stress became uncompensable. For each condition, we compared heat storage () and the change in gastrointestinal temperature (Δ) over time during compensable and uncompensable heat stress. In addition, we examined whether individual characteristics or seasonality were associated with the rate of increase in . During compensable heat stress, was higher in HD than in WH environments ( < 0.05) resulting in a greater but more variable Δ ( ≥ 0.06) for both metabolic rates. There were no differences among conditions during uncompensable heat stress (all > 0.05). There was no influence of sex, aerobic fitness, or seasonality, but a larger body size was associated with a greater Δ during LightAmb in WH ( = 0.003). The slopes of the response during compensable (WH: MinAct, 0.06, LightAmb, 0.09; HD: MinAct, 0.12, LightAmb, 0.15°C/h) and uncompensable (WH: MinAct, 0.74, LightAmb, 0.87; HD: MinAct, 0.71, LightAmb, 0.93°C/h) heat stress can be used to estimate the time to reach a target core temperature from any given starting value. This study is the first to examine heat storage and the rate of change in core temperature above (uncompensable heat stress) and just below (compensable heat stress) critical environmental limits to human heat balance. Furthermore, we examine the influence of individual subject characteristics and seasonality on the change in core temperature in warm-humid versus hot-dry environments. We provide the rate of change in core temperature, enabling projections to be made to and from any hypothetical core temperature.
随着全球变暖，人们越来越关注人类适应能力的上限。然而，达到普遍接受的核心温度标准（40.2°C）的时间仍然不清楚，这个标准与热相关疾病有关，高于这个标准（不可补偿的热应激）和低于这个标准（可补偿的热应激）分别代表着热平衡的上限和下限。48 名（22 名男性/26 名女性；23±4 岁）受试者在环境室中进行最小活动（MinAct，159±34 W）和轻度步行（LightAmb，260±55 W）时，在温暖潮湿（WH；约 35°C，>60%RH）和炎热干燥（HD；43°C-48°C，<25%RH）环境中逐渐暴露于热应激下，直到热应激变得不可补偿。对于每种情况，我们比较了可补偿和不可补偿热应激期间热量储存（）和胃肠道温度变化（Δ）随时间的变化。此外，我们还研究了个体特征或季节性是否与增加率有关。在可补偿热应激期间，HD 环境中的高于 WH 环境（<0.05），导致代谢率较高但变化更大的（≥0.06）。在不可补偿热应激期间，各条件之间没有差异（均>0.05）。性别、有氧健身或季节性没有影响，但体型较大与 WH 环境中 LightAmb 期间更大的Δ有关（=0.003）。可补偿（WH：MinAct，0.06，LightAmb，0.09；HD：MinAct，0.12，LightAmb，0.15°C/h）和不可补偿（WH：MinAct，0.74，LightAmb，0.87；HD：MinAct，0.71，LightAmb，0.93°C/h）热应激期间的响应斜率可以用来估计从任何给定起始值达到目标核心温度的时间。这项研究首次检查了在人类热平衡的关键环境限制之上（不可补偿的热应激）和之下（可补偿的热应激）储存热量和核心温度变化率。此外，我们还研究了个体受试者特征和季节性对温暖潮湿与炎热干燥环境中核心温度变化的影响。我们提供了核心温度的变化率，使人们能够对任何假设的核心温度进行预测。
