Meade Robert D, Kenny Glen P
Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Montpetit Hall, Ottawa, CANADA.
Med Sci Sports Exerc. 2017 Sep;49(9):1796-1804. doi: 10.1249/MSS.0000000000001309.
We evaluated physiological responses during exercise at a fixed evaporative requirement for heat balance (Ereq) but varying combinations of metabolic and environmental heat load.
Nine healthy, physically active males (age: 46 ± 8 yr) performed four experimental sessions consisting of 75 min of semirecumbent cycling at various ambient temperatures. Whole-body dry heat loss (direct calorimetry) was monitored continuously as was heat production (indirect calorimetry), which was adjusted to achieve an Ereq of 400 W. The resultant metabolic heat productions and ambient temperatures for the sessions were as follows: (i) 440 W and 30°C (440 [30]), (ii) 388 W and 35°C (388 [35]), (iii) 317 W and 40°C (317 [40]), and (iv) 258 W and 45°C (258 [45]). Whole-body evaporative heat loss was determined via direct calorimetry. Esophageal (Tes) and mean skin (Tsk) temperatures as well as HR were monitored continuously. Mean body temperature (Tb) was calculated from Tes and Tsk. Physiological strain index (PSI) was determined from Tes and HR.
End-exercise evaporative heat loss and Tb were similar between conditions (both P ≥ 0.48). Tes was greater in 440 [30] (37.67°C ± 0.04°C) and 388 [35] (37.58°C ± 0.07°C) relative to both 317 [40] (37.35°C ± 0.06°C) and 258 [45] (37.20°C ± 0.07°C; all P ≤ 0.05). Further, Tsk was different between each condition (440 [30], 33.85°C ± 0.16°C; 388 [35], 34.53°C ± 0.08°C; 317 [40], 35.67°C ± 0.07°C; and 258 [45], 36.54°C ± 0.08°C; all P < 0.01). In 440 [30], HR was elevated by about 13 and 18 bpm relative to 317 [40] and 258 [45], respectively (both P < 0.01). Finally, PSI was greater in both 440 [30] and 388 [35] compared with 317 [40] and 258 [45] (all P ≤ 0.04).
Exercise at a fixed Ereq resulted in similar evaporative heat loss and Tb. However, the Tes, Tsk, HR, and PSI responses varied depending on the relative contribution of metabolic and environmental heat load.
我们评估了在固定的用于热平衡的蒸发需求（Ereq）下，但代谢热负荷和环境热负荷组合不同时运动期间的生理反应。
九名健康、有体育锻炼习惯的男性（年龄：46±8岁）进行了四个实验阶段，包括在不同环境温度下进行75分钟的半卧位骑行。持续监测全身干热损失（直接量热法）以及产热（间接量热法），并进行调整以实现400W的Ereq。各阶段的代谢产热和环境温度如下：（i）440W和30°C（440[30]），（ii）388W和35°C（388[35]），（iii）317W和40°C（317[40]），以及（iv）258W和45°C（258[45]）。通过直接量热法测定全身蒸发散热。持续监测食管温度（Tes）、平均皮肤温度（Tsk）以及心率（HR）。根据Tes和Tsk计算平均体温（Tb）。根据Tes和HR确定生理应变指数（PSI）。
各条件下运动结束时的蒸发散热和Tb相似（两者P≥0.48）。相对于317[40]（37.35°C±0.06°C）和258[45]（37.20°C±0.07°C），Tes在440[30]（37.67°C±0.04°C）和388[35]（37.58°C±0.07°C）时更高（所有P≤0.05）。此外，各条件下Tsk不同（440[30]，33.85°C±0.16°C；388[35]，34.53°C±0.08°C；317[40]，35.67°C±0.07°C；258[45]，36.54°C±0.08°C；所有P<0.01）。在440[30]时，HR相对于317[40]和258[45]分别升高约13次/分钟和18次/分钟（两者P<0.01）。最后，与317[40]和258[45]相比，440[30]和388[35]时的PSI更高（所有P≤0.04）。
在固定Ereq下运动导致相似的蒸发散热和Tb。然而，Tes、Tsk、HR和PSI反应因代谢热负荷和环境热负荷的相对贡献而异。
