Notley Sean R, Poirier Martin P, Hardcastle Stephen G, Flouris Andreas D, Boulay Pierre, Sigal Ronald J, Kenny Glen P
1Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA; 2BBE Consulting Canada, Copper Cliff, Ontario, CANADA; 3FAME Laboratory, Department of Exercise Science, University of Thessaly, Trikala, GREECE; 4Faculty of Physical Activity Sciences, University of Sherbrooke, Sherbrooke, Quebec, CANADA; 5Departments of Medicine, Cardiac Sciences and Community Health Sciences, Faculties of Medicine and Kinesiology, University of Calgary, Calgary, Alberta, CANADA; and 6Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, CANADA.
Med Sci Sports Exerc. 2017 Nov;49(11):2324-2332. doi: 10.1249/MSS.0000000000001342.
This study was designed to determine whether age-related impairments in whole-body heat loss, which are known to exist in dry heat, also occur in humid heat in women.
To evaluate this possibility, 10 young (25 ± 4 yr) and 10 older (51 ± 7 yr) women matched for body surface area (young, 1.69 ± 0.11; older, 1.76 ± 0.14 m, P = 0.21) and peak oxygen consumption (V˙O2peak) (young, 38.6 ± 4.6; older, 34.8 ± 6.6 mL·kg·min, P = 0.15) performed four 15-min bouts of cycling at a fixed metabolic heat production rate (300 W; equivalent to ~45% V˙O2peak), each separated by a 15-min recovery, in dry (35°C, 20% relative humidity) and humid heat (35°C, 60% 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 measured as the temporal summation of heat production and loss.
Total heat loss was lower in humid conditions compared with dry conditions during all exercise bouts in both groups (all P < 0.05), resulting in 49% and 39% greater body heat storage in young and older women, respectively (both P < 0.01). Total heat loss was also lower in older women compared with young women during exercise bouts 1, 2 and 3 in dry heat (all P < 0.05) and bouts 1 and 2 in humid heat (both P < 0.05). Consequently, body heat storage was 29% and 16% greater in older women compared with young women in dry and humid conditions, respectively (both P < 0.05).
Increasing ambient humidity reduces heat loss capacity in young and older women. However, older women display impaired heat loss relative to young women in both dry and humid heat, and may therefore be at greater risk of heat-related injury during light-to-moderate activity.
本研究旨在确定已知在干热环境中存在的与年龄相关的全身散热受损情况在女性湿热环境中是否也会出现。
为评估这种可能性，选取了10名年轻女性（25±4岁）和10名年长女性（51±7岁），她们在体表面积（年轻女性为1.69±0.11；年长女性为1.76±0.14平方米，P = 0.21）和峰值耗氧量（V˙O2peak）（年轻女性为38.6±4.6；年长女性为34.8±6.6毫升·千克·分钟，P = 0.15）方面相匹配。她们在干热（35°C，相对湿度20%）和湿热（35°C，相对湿度60%）环境下，以固定的代谢产热率（300瓦；相当于约45%V˙O2peak）进行了四组15分钟的骑行运动，每组运动之间间隔15分钟的恢复时间。分别使用直接量热法和间接量热法测量总散热量（蒸发散热±干热交换）和代谢产热。通过产热和散热的时间总和来测量身体的蓄热情况。
在两组的所有运动时段中，湿热环境下的总散热量均低于干热环境（所有P < 0.05），导致年轻女性和年长女性的身体蓄热分别增加了49%和39%（均P < 0.01）。在干热环境下的第1、2和3组运动时段以及湿热环境下的第1和2组运动时段中，年长女性的总散热量也低于年轻女性（所有P < 0.05）。因此，在干热和湿热环境中，年长女性的身体蓄热分别比年轻女性高29%和16%（均P < 0.05）。
环境湿度增加会降低年轻女性和年长女性的散热能力。然而，在干热和湿热环境中，年长女性相对于年轻女性的散热能力受损，因此在轻度至中度活动期间可能面临更高的与热相关损伤的风险。
