Larose Joanie, Boulay Pierre, Sigal Ronald J, Wright Heather E, Kenny Glen P
Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Canada.
Faculty of Physical Education and Sports, University of Sherbrooke, Sherbrooke, Canada.
PLoS One. 2013 Dec 12;8(12):e83148. doi: 10.1371/journal.pone.0083148. eCollection 2013.
Older adults typically experience greater levels of thermal strain during physical efforts in the heat compared to young individuals. While this may be related to an age-dependent reduction in whole-body sweating, no study has clearly delineated at what age this occurs. In the present study, we report direct measurements of human heat dissipation during physical activity in the heat in males ranging in age from 20-70 years. Eighty-five males performed four 15-min bouts of cycling separated by 15-min rest periods, in a calorimeter regulated to 35°C and 20% relative humidity. Direct calorimetry was used to measure total heat loss (whole-body evaporative heat loss and dry heat exchange). We also used indirect calorimetry as a continuous measure of metabolic heat production. Body heat storage was calculated as the temporal summation of heat production and total heat loss over the experimental session. Whole-body sweat rate (WBSR) was calculated from measurements of evaporative heat loss. Males were divided into five age categories for the analysis of WBSR and body heat storage: 20-31 years (n = 18), 40-44 years (n = 15), 45-49 years (n = 15), 50-55 years (n = 21) and 56-70 years (n = 16). Relative to young males, WBSR was reduced in males aged 56-70 during each exercise (all P<0.05), in males aged 50-55 during the second (P = 0.031) and third exercises (P = 0.028) and in males aged 45-49 during the final exercise bout (P = 0.046). Although not significantly different, 40-44 years old males also had a lower rate of heat loss compared to younger males. Over the sum of two hours, the change in body heat content was greater in males 40-70 years compared to young males (all P<0.05). Our findings suggest that middle-aged and older adults have impairments in heat dissipation when doing physical activity in the heat, thus possibly increasing their risk of heat-related illness under such conditions.
与年轻人相比，老年人在炎热环境中进行体力活动时通常会经历更高水平的热应激。虽然这可能与全身出汗随年龄增长而减少有关，但尚无研究明确说明这种情况发生在什么年龄。在本研究中，我们报告了年龄在20至70岁之间的男性在炎热环境中进行体力活动时人体散热的直接测量结果。85名男性在调节至35°C和20%相对湿度的热量计中进行了四组15分钟的骑行，每组之间有15分钟的休息时间。直接量热法用于测量总热量损失（全身蒸发散热和干热交换）。我们还使用间接量热法作为代谢产热的连续测量方法。身体热量储存通过实验过程中产热和总热量损失的时间总和来计算。全身出汗率（WBSR）通过蒸发散热的测量值来计算。男性被分为五个年龄组以分析WBSR和身体热量储存：20至31岁（n = 18）、40至44岁（n = 15）、45至49岁（n = 15）、50至55岁（n = 21）和56至70岁（n = 16）。与年轻男性相比，56至70岁的男性在每次运动期间WBSR降低（所有P<0.05），50至55岁的男性在第二次（P = 0.031）和第三次运动期间（P = 0.028）以及45至49岁的男性在最后一次运动回合期间（P = 0.046）WBSR降低。尽管差异不显著，但40至44岁的男性与年轻男性相比散热率也较低。在两小时的总和中，40至70岁的男性身体热量含量的变化比年轻男性更大（所有P<0.05）。我们的研究结果表明，中年和老年人在炎热环境中进行体力活动时散热存在障碍，因此在这种情况下可能会增加他们患热相关疾病的风险。
