Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, 125 University Private, Room 367 Montpetit Hall, Ottawa, ON, K1N 6N5, Canada.
Eur J Appl Physiol. 2020 Dec;120(12):2665-2675. doi: 10.1007/s00421-020-04486-3. Epub 2020 Sep 9.
Time-weighted averaging is used in occupational heat stress guidelines to estimate the metabolic demands of variable-intensity work. However, compared to constant-intensity work of the same time-weighted average metabolic rate, variable-intensity work may cause decrements in total heat loss (dry + evaporative heat loss) that exacerbate heat storage in women. We therefore used direct calorimetry to assess whole-body total heat loss and heat storage (metabolic heat production minus total heat loss) in women and men during constant- and variable-intensity work of equal average intensity.
Ten women [mean (SD); 31 (11) years] and fourteen men [30 (8) years] completed two trials involving 90-min of constant- and variable-intensity work (cycling) eliciting an average metabolic heat production of ~ 200 W/m in dry-heat (40 °C, ~ 15% relative humidity). External work was fixed at ~ 40 W/m for constant-intensity work, and alternated between ~ 15 and ~ 60 W/m (5-min each) for variable-intensity work.
When expressed as a time-weighted average over each work period, total heat loss did not differ between men and women (mean difference [95% CI]; 4 W/m [- 11, 20]; p = 0.572) or between constant- and variable-intensity work (1 W/m [- 3, 5]; p = 0.642). Consequently, heat storage did not differ significantly between men and women (- 4 W/m [- 17, 8]; p = 0.468) or between constant- and variable-intensity work (0 W/m [- 3, 3]; p = 0.834).
Neither whole-body heat loss nor heat storage was modulated by the partitioning of work intensity, indicating that time-weighted averaging is appropriate for estimating metabolic demand to assess occupational heat stress in women.
时间加权平均法被用于职业性热应激指南，以估计强度可变的工作的代谢需求。然而，与强度不变的工作相比，强度可变的工作可能导致总热损失（干热损失加蒸发热损失）减少，从而加剧女性的热量蓄积。因此，我们使用直接测热法评估了女性和男性在等平均强度的恒温和变强度工作期间的全身总热损失和热蓄积（代谢产热减去总热损失）。
10 名女性（平均[标准差]；31[11]岁）和 14 名男性（30[8]岁）完成了两项试验，每项试验包括 90 分钟的恒温和变强度工作（骑自行车），平均代谢产热量为 200W/m2在干燥热（40°C，相对湿度约 15%）中。恒强度工作的外部工作固定在 40W/m2左右，变强度工作的外部工作在 15 和 60W/m2（每 5 分钟一次）之间交替。
当以每个工作期间的时间加权平均值表示时，男性和女性之间的总热损失没有差异（平均差异[95%置信区间]；4W/m[-11,20]；p=0.572），也没有在恒强度和变强度工作之间差异（1W/m[-3,5]；p=0.642）。因此，男性和女性之间的热蓄积也没有显著差异（-4W/m[-17,8]；p=0.468），或者在恒强度和变强度工作之间差异（0W/m[-3,3]；p=0.834）。
工作强度的分配既没有调节全身热损失，也没有调节热蓄积，这表明时间加权平均法适合于估计代谢需求，以评估女性的职业性热应激。
