Ravanelli Nicholas, Gagnon Daniel, Imbeault Pascal, Jay Ollie
Cardiovascular Prevention and Rehabilitation Centre and Research Centre, Montreal Heart Institute, Montreal, QC, Canada.
Département de pharmacologie et physiologie, Université de Montréal, Montreal, QC, Canada.
Exp Physiol. 2021 Jan;106(1):282-289. doi: 10.1113/EP088385. Epub 2020 Mar 18.
What is the central question of this study? Are fitness-related improvements in thermoregulatory responses during uncompensable heat stress mediated by aerobic capacity or is it the partial heat acclimation associated with training? What is the main finding and its importance? During uncompensable heat stress, individuals with high and low displayed similar sweating and core temperature responses whereas exercise training in previously untrained individuals resulted in a greater sweat rate and a smaller rise in core temperature. These observations suggest that it is training, not per se, that mediates thermoregulatory improvements during uncompensable heat stress.
It remains unclear whether aerobic fitness, as defined by the maximum rate of oxygen consumption , independently improves heat dissipation in uncompensable environments, or whether the thermoregulatory adaptations associated with heat acclimation are due to repeated bouts of exercise-induced heat stress during regular aerobic training. The present analysis sought to determine if independently influences thermoregulatory sweating, maximum skin wettedness (ω ) and the change in rectal temperature (ΔT ) during 60 min of exercise in an uncompensable environment (37.0 ± 0.8°C, 4.0 ± 0.2 kPa, 64 ± 3% relative humidity) at a fixed rate of heat production per unit mass (6 W kg ). Retrospective analyses were performed on 22 participants (3 groups), aerobically unfit (UF; n = 7; : 41.7 ± 9.4 ml kg min ), aerobically fit (F; n = 7; : 55.6 ± 4.3 ml kg min ; P < 0.01) and aerobically unfit (n = 8) individuals, before (pre; : 45.8 ± 11.6 ml kg min ) and after (post; : 52.0 ± 11.1 ml kg min ; P < 0.001) an 8-week training intervention. ω was similar between UF (0.74 ± 0.09) and F (0.78 ± 0.08, P = 0.22). However, ω was greater post- (0.84 ± 0.08) compared to pre- (0.72 ± 0.06, P = 0.02) training. During exercise, mean local sweat rate (forearm and upper-back) was greater post- (1.24 ± 0.20 mg cm min ) compared to pre- (1.04 ± 0.25 mg cm min , P < 0.01) training, but similar between UF (0.94 ± 0.31 mg cm min , P = 0.90) and F (1.02 ± 0.30 mg cm min ). The ΔT at 60 min of exercise was greater pre- (1.13 ± 0.16°C, P < 0.01) compared to post- (0.96 ± 0.14°C) training, but similar between UF (0.85 ± 0.29°C, P = 0.22) and F (0.95 ± 0.22°C). Taken together, aerobic training, not per se, confers an increased ω , greater sweat rate, and smaller rise in core temperature during uncompensable heat stress in fit individuals.
本研究的核心问题是什么？在无法代偿的热应激期间，与体能相关的体温调节反应改善是由有氧能力介导的，还是与训练相关的部分热适应所致？主要发现及其重要性是什么？在无法代偿的热应激期间，体能高低不同的个体出汗和核心体温反应相似，而此前未经训练的个体进行运动训练后，出汗率更高，核心体温上升幅度更小。这些观察结果表明，在无法代偿的热应激期间，介导体温调节改善的是训练本身，而非有氧能力。
目前尚不清楚，以最大耗氧率（ ）定义的有氧适能是否能在无法代偿的环境中独立改善散热，或者与热适应相关的体温调节适应是否归因于常规有氧训练期间反复出现的运动诱导热应激。本分析旨在确定，在无法代偿的环境（37.0±0.8°C、4.0±0.2kPa、相对湿度64±3%）中，以固定的单位质量产热率（6W/kg）进行60分钟运动期间，有氧适能是否会独立影响体温调节性出汗、最大皮肤湿润度（ω）和直肠温度变化（ΔT）。对22名参与者（3组）进行回顾性分析，这3组分别为有氧不适能（UF；n=7； ：41.7±9.4ml·kg⁻¹·min⁻¹）、有氧适能（F；n=7； ：55.6±4.3ml·kg⁻¹·min⁻¹；P<0.01）以及有氧不适能（n=8）个体，分析他们在8周训练干预前后（干预前； ：45.8±11.6ml·kg⁻¹·min⁻¹）（干预后； ：52.0±11.1ml·kg⁻¹·min⁻¹；P<0.001）的情况。UF组（0.74±0.09）和F组（0.78±0.08，P=0.22）的ω相似。然而，与训练前（0.72±0.06，P=0.02）相比，训练后（0.84±0.08）的ω更高。运动期间，训练后（1.24±0.20mg·cm⁻²·min⁻¹）的平均局部出汗率（前臂和上背部）高于训练前（1.04±0.25mg·cm⁻²·min⁻¹，P<0.01），但UF组（0.94±0.31mg·cm⁻²·min⁻¹，P=0.90）和F组（1.02±0.30mg·cm⁻²·min⁻¹）相似。运动60分钟时的ΔT训练前（1.13±0.16°C，P<0.01）高于训练后（0.96±0.14°C），但UF组（0.85±0.29°C，P=0.22）和F组（0.95±0.22°C）相似。综上所述，在适能个体的无法代偿热应激期间，是有氧训练而非有氧适能本身，带来了更高的ω、更大的出汗率以及更小的核心体温上升幅度。
