Stapleton Jill M, Poirier Martin P, Flouris Andreas D, Boulay Pierre, Sigal Ronald J, Malcolm Janine, Kenny Glen P
Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada.
FAME Laboratory, Department of Exercise Science, University of Thessaly, Trikala, Greece.
PLoS One. 2015 Mar 19;10(3):e0119079. doi: 10.1371/journal.pone.0119079. eCollection 2015.
Studies have reported that older females have impaired heat loss responses during work in the heat compared to young females. However, it remains unclear at what level of heat stress these differences occur. Therefore, we examined whole-body heat loss [evaporative (HE) and dry heat loss, via direct calorimetry] and changes in body heat storage (∆Hb, via direct and indirect calorimetry) in 10 young (23±4 years) and 10 older (58±5 years) females matched for body surface area and aerobic fitness (VO2peak) during three 30-min exercise bouts performed at incremental rates of metabolic heat production of 250 (Ex1), 325 (Ex2) and 400 (Ex3) W in the heat (40°C, 15% relative humidity). Exercise bouts were separated by 15 min of recovery. Since dry heat gain was similar between young and older females during exercise (p=0.52) and recovery (p=0.42), differences in whole-body heat loss were solely due to HE. Our results show that older females had a significantly lower HE at the end of Ex2 (young: 383±34 W; older: 343±39 W, p=0.04) and Ex3 (young: 437±36 W; older: 389±29 W, p=0.008), however no difference was measured at the end of Ex1 (p=0.24). Also, the magnitude of difference in the maximal level of HE achieved between the young and older females became greater with increasing heat loads (Ex1=10.2%, Ex2=11.6% and Ex3=12.4%). Furthermore, a significantly greater ∆Hb was measured for all heat loads for the older females (Ex1: 178±44 kJ; Ex2: 151±38 kJ; Ex3: 216±25 kJ, p=0.002) relative to the younger females (Ex1: 127±35 kJ; Ex2: 96±45 kJ; Ex3: 146±46 kJ). In contrast, no differences in HE or ∆Hb were observed during recovery (p>0.05). We show that older habitually active females have an impaired capacity to dissipate heat compared to young females during exercise-induced heat loads of ≥325 W when performed in the heat.
研究报告称，与年轻女性相比，年长女性在高温环境下工作时散热反应受损。然而，尚不清楚这些差异在何种热应激水平下出现。因此，我们通过直接量热法检测了10名年轻女性（23±4岁）和10名年长女性（58±5岁）在40°C、相对湿度15%的高温环境下，以250（Ex1）、325（Ex2）和400（Ex3）W的代谢产热递增速率进行的三次30分钟运动期间的全身散热[蒸发散热（HE）和干热散失]以及身体热储存变化（∆Hb，通过直接和间接量热法）。运动回合之间有15分钟的恢复时间。由于年轻女性和年长女性在运动期间（p = 0.52）和恢复期间（p = 0.42）的干热获得相似，全身散热的差异仅归因于蒸发散热。我们的结果表明年长女性在Ex2结束时（年轻女性：383±34 W；年长女性：343±39 W，p = 0.04）和Ex3结束时（年轻女性：437±36 W；年长女性：389±29 W，p = 0.008）的蒸发散热显著更低，然而在Ex1结束时未测得差异（p = 0.24）。此外，随着热负荷增加，年轻女性和年长女性之间达到的最大蒸发散热水平的差异幅度变得更大（Ex1 = 10.2%，Ex2 = 11.6%，Ex3 = 12.4%）。此外，相对于年轻女性（Ex1：127±35 kJ；Ex2：96±45 kJ；Ex3：1 I46±46 kJ），年长女性在所有热负荷下测得的∆Hb显著更高（Ex1：178±44 kJ；Ex2：151±38 kJ；Ex3：216±25 kJ，p = 0.002）。相比之下，恢复期间未观察到蒸发散热或∆Hb的差异（p>0.05）。我们表明，在高温环境下进行≥325 W的运动诱导热负荷时，习惯活跃的年长女性与年轻女性相比散热能力受损。
