Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA.
Med Sci Sports Exerc. 2018 Feb;50(2):318-326. doi: 10.1249/MSS.0000000000001444.
Heat strain is known to be exacerbated on the second of consecutive work days. We therefore evaluated whether prolonged work in the heat would impair whole-body heat loss capacity on the next day.
To evaluate this possibility, we assessed changes in whole-body heat exchange and heat storage in eight young (26 ± 4 yr) men during heat stress tests performed on the same day before (day 1) and on the day after (day 2) a prolonged work simulation. Each heat stress test involved three, 30-min bouts of semirecumbent cycling at fixed rates of metabolic heat production (200 W·m (Ex1), 250 W·m (Ex2), and 300 W·m (Ex3)), each separated by 15-min recovery, under hot, dry conditions (40°C, 20% relative humidity). The work simulation (7.5 h) involved three moderate-intensity intermittent work bouts (2 h), each separated by 30-min rest breaks, under similarly hot, dry conditions (38°C, 34% relative humidity). Total heat loss (evaporative ± dry heat exchange) and metabolic heat production were measured using direct and indirect calorimetry, respectively. Body heat storage was quantified as the temporal summation of heat production and loss.
Total heat loss did not differ between days 1 and 2 (P = 0.66) and averaged (mean ± 95% confidence interval) 185 ± 7 W (Ex1), 233 ± 7 W (Ex2), and 261 ± 5 W (Ex3) across test days. Consequently, the change in body heat storage was also similar between days 1 and 2 (P = 0.32), averaging 133 ± 15 kJ (Ex1), 99 ± 16 kJ (Ex2), and 184 ± 15 kJ (Ex3) across test days.
When assessed under controlled laboratory conditions in young men, prolonged work in the heat does not seem to impair whole-body heat loss or exacerbate heat storage on the following day.
已知在连续工作日的第二天，热应激会加剧。因此，我们评估了在热环境中长时间工作是否会在下一天损害全身散热能力。
为了评估这种可能性，我们评估了 8 名年轻男性（26 ± 4 岁）在同一天（第 1 天）和第二天（第 2 天）进行长时间工作模拟前后进行热应激测试时全身热交换和热量储存的变化。在每个热应激测试中，参与者以固定的代谢产热率（200 W·m（Ex1）、250 W·m（Ex2）和 300 W·m（Ex3））进行 3 次 30 分钟的半卧位自行车运动，每次运动之间有 15 分钟的恢复期，在炎热干燥的条件下（40°C，20%相对湿度）进行。工作模拟（7.5 小时）包括 3 次中等强度的间歇性工作，每次工作之间有 30 分钟的休息时间，在同样炎热干燥的条件下（38°C，34%相对湿度）进行。使用直接和间接测热法分别测量总热损失（蒸发+干热交换）和代谢产热。身体热量储存通过热量产生和损失的时间总和来量化。
第 1 天和第 2 天之间的总热损失没有差异（P = 0.66），平均（平均值 ± 95%置信区间）分别为 185 ± 7 W（Ex1）、233 ± 7 W（Ex2）和 261 ± 5 W（Ex3）在测试日。因此，第 1 天和第 2 天之间的体热储存变化也相似（P = 0.32），平均分别为 133 ± 15 kJ（Ex1）、99 ± 16 kJ（Ex2）和 184 ± 15 kJ（Ex3）在测试日。
在年轻男性的受控实验室条件下进行评估时，长时间在热环境中工作似乎不会在下一天损害全身散热能力或加剧体热储存。
