Mr Jesse Criddle, Mr Andrew Haynes, Mr Howard H. Carter, Ms Julie Collis, Ms Kristanti Wigati, Ms Juliene Goncalves Costa Dechichi, Mr Joao Carlos Loacatelli, Prof Robert McLaughlin, Daniel Green
{"title":"DETERMINANTS OF PHYSIOLOGICAL RESPONSE TO EXERTIONAL HEAT STRESS IN HUMANS","authors":"Mr Jesse Criddle, Mr Andrew Haynes, Mr Howard H. Carter, Ms Julie Collis, Ms Kristanti Wigati, Ms Juliene Goncalves Costa Dechichi, Mr Joao Carlos Loacatelli, Prof Robert McLaughlin, Daniel Green","doi":"10.31189/2165-7629-13-s2.408","DOIUrl":null,"url":null,"abstract":"\n \n Previous field studies of exercise undertaken in hot conditions reported dissociation between heat-related symptoms and body core temperature (Tc) elevation. This prompted us to examine physiological mechanisms underpinning responses to exertional heat exposure in a controlled laboratory experiment.\n \n \n \n Thirty-eight apparently healthy participants had body composition (DEXA) and fitness (V̇O2peak) measured in a preliminary visit. Tc, heart rate (HR), exercise intensity (V̇O2) and echocardiographic measures of end-diastolic volume (EDV), stroke volume (SV) and cardiac output (Q̇) were measured at rest and at 30-minute intervals throughout a two-hour walk (5km/h and 2% gradient) in a climate-controlled chamber (40⸰C and 50% relative-humidity).\n \n \n \n Twenty-seven participants completed the experiment (Completers; Com), 7 were stopped due to Tc exceeding 39⸰C (Hyperthermics; Hyp). Four participants did not complete the protocol due to adverse symptoms and were excluded from this analysis. Hyp had significantly greater Tc at 60-minutes (38.6±0.5⸰C vs. 38.0±0.3⸰C; P=<0.001) and 90-minutes (39.0±0.3⸰C vs. 38.3±0.3⸰C; P=<0.001) than Com. Baseline V̇O2peak (ml.kg-1.min-1) did not differ between Hyp and Com (P=0.248). Whilst body weight and lean body mass did not significantly differ between Hyp and Com, visceral adipose tissue (VAT) volume (463.2±194.3cm3 vs. 259.9±284.4cm3 P=0.014) and mass (437.0±183.1g vs. 245.2±268.2g P=0.013) were significantly greater in Hyp vs Com. In Hyp, HR change from baseline was greater at 60-minutes (Δ57±15bpm vs. Δ36±18bpm; P=0.01) and 90-minutes (Δ63±20bpm vs. Δ42±19bpm; P=0.017), whilst change in EDV (Δ-22.7±11.4ml vs. Δ-6.92±11.2ml; P=0.016) and SV (Δ-19.4±6.1ml vs. Δ-0.7±7.5ml; P=<0.001) were significantly reduced in Hyp compared to Com.\n \n \n \n During walking in the heat, subjects who became hyperthermic had significantly higher baseline visceral fat mass and early signs of exaggerated haemodynamic burden during exertional heat exposure. This study has implications for the identification of appropriate variables for establishing safe work limits during heat exposure in military and work-related contexts.\n","PeriodicalId":92070,"journal":{"name":"Journal of clinical exercise physiology","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of clinical exercise physiology","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.31189/2165-7629-13-s2.408","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
Previous field studies of exercise undertaken in hot conditions reported dissociation between heat-related symptoms and body core temperature (Tc) elevation. This prompted us to examine physiological mechanisms underpinning responses to exertional heat exposure in a controlled laboratory experiment.
Thirty-eight apparently healthy participants had body composition (DEXA) and fitness (V̇O2peak) measured in a preliminary visit. Tc, heart rate (HR), exercise intensity (V̇O2) and echocardiographic measures of end-diastolic volume (EDV), stroke volume (SV) and cardiac output (Q̇) were measured at rest and at 30-minute intervals throughout a two-hour walk (5km/h and 2% gradient) in a climate-controlled chamber (40⸰C and 50% relative-humidity).
Twenty-seven participants completed the experiment (Completers; Com), 7 were stopped due to Tc exceeding 39⸰C (Hyperthermics; Hyp). Four participants did not complete the protocol due to adverse symptoms and were excluded from this analysis. Hyp had significantly greater Tc at 60-minutes (38.6±0.5⸰C vs. 38.0±0.3⸰C; P=<0.001) and 90-minutes (39.0±0.3⸰C vs. 38.3±0.3⸰C; P=<0.001) than Com. Baseline V̇O2peak (ml.kg-1.min-1) did not differ between Hyp and Com (P=0.248). Whilst body weight and lean body mass did not significantly differ between Hyp and Com, visceral adipose tissue (VAT) volume (463.2±194.3cm3 vs. 259.9±284.4cm3 P=0.014) and mass (437.0±183.1g vs. 245.2±268.2g P=0.013) were significantly greater in Hyp vs Com. In Hyp, HR change from baseline was greater at 60-minutes (Δ57±15bpm vs. Δ36±18bpm; P=0.01) and 90-minutes (Δ63±20bpm vs. Δ42±19bpm; P=0.017), whilst change in EDV (Δ-22.7±11.4ml vs. Δ-6.92±11.2ml; P=0.016) and SV (Δ-19.4±6.1ml vs. Δ-0.7±7.5ml; P=<0.001) were significantly reduced in Hyp compared to Com.
During walking in the heat, subjects who became hyperthermic had significantly higher baseline visceral fat mass and early signs of exaggerated haemodynamic burden during exertional heat exposure. This study has implications for the identification of appropriate variables for establishing safe work limits during heat exposure in military and work-related contexts.
以往对高温条件下运动的实地研究报告称,热相关症状与身体核心温度(Tc)升高之间并无关联。这促使我们在一项受控实验室实验中,研究了支撑运动性热暴露反应的生理机制。 38 名表面健康的参与者在初步访问中测量了身体成分(DEXA)和体能(V̇O2peak)。在气候控制室(40⸰C,相对湿度为 50%)中进行了两小时的步行(时速 5 公里,坡度 2%),在休息时和每隔 30 分钟测量一次 Tc、心率(HR)、运动强度(VO2)以及舒张末期容积(EDV)、每搏量(SV)和心输出量(Q)等超声心动图测量指标。 27 名参与者完成了实验(Completters;Com),7 名参与者因 Tc 超过 39⸰C(Hyperthermics;Hyp)而停止实验。有四名参与者因出现不良症状而未完成实验,不在分析之列。60分钟(38.6±0.5⸰C vs. 38.0±0.3⸰C;P=<0.001)和90分钟(39.0±0.3⸰C vs. 38.3±0.3⸰C;P=<0.001)时,Hyp的Tc明显高于Com。Hyp 和 Com 的基线 V̇O2peak(ml.kg-1.min-1)没有差异(P=0.248)。虽然体重和瘦体重在 Hyp 和 Com 之间没有显著差异,但内脏脂肪组织(VAT)体积(463.2±194.3 立方厘米 vs. 259.9±284.4 立方厘米,P=0.014)和质量(437.0±183.1 克 vs. 245.2±268.2 克,P=0.013)在 Hyp 和 Com 之间显著增加。在 Hyp 中,60 分钟(Δ57±15bpm vs. Δ36±18bpm;P=0.01)和 90 分钟(Δ63±20bpm vs. Δ42±19bpm;P=0.017),而与Com相比,Hyp的EDV变化(Δ-22.7±11.4ml vs. Δ-6.92±11.2ml;P=0.016)和SV变化(Δ-19.4±6.1ml vs. Δ-0.7±7.5ml;P=<0.001)显著减少。 在高温下行走时,出现高热的受试者的基线内脏脂肪量明显较高,并且在用力受热时会出现血流动力学负担加重的早期迹象。这项研究有助于确定适当的变量,以便在军事和工作环境中确定热暴露期间的安全工作限制。