TY - JOUR

T1 - A comparison of heat acclimation by post-exercise hot water immersion and exercise in the heat

AU - McIntyre, Robert

AU - Mee, Jessica

AU - Zurawlew, Michael

AU - Oliver, Sam

AU - Cox, Andrew

AU - Walsh, Neil

N1 - 24 months embargo

PY - 2021/8/1

Y1 - 2021/8/1

N2 - ObjectivesTo compare heat acclimation adaptations after three and six days of either post-exercise hot water immersion (HWI) or exercise-heat-acclimation (EHA) in recreationally active individuals.DesignRandomised, mixed model, repeated measures.MethodsPost-exercise HWI involved a daily 40-min treadmill-run at 65% V̇O2peak in temperate conditions (19°C, 45% RH) followed by HWI (≤ 40 min, 40°C water; n=9). Daily EHA involved a ≤60-min treadmill-run in the heat (65% V̇O2peak; 33°C, 40% RH; n=9), chosen to elicit a similar endogenous thermal stimulus to HWI. A thermoneutral exercise intervention (TNE, 19°C, 45% RH; n=9), work-matched to EHA, was also included to determine thermoregulatory adaptations to daily exercise in temperate conditions. An exercise heat-stress-test was performed before and after three and six intervention days and involved a 40-min treadmill-run and time-to-exhaustion (TTE) at 65% V̇O2peak in the heat (33°C, 40% RH).ResultsANCOVA, using baseline values as the covariate, revealed no interaction effects but significant group effects demonstrated that compared to EHA, HWI elicited larger reductions in resting rectal temperature (Tre; p=0.021), Tre at sweating onset (p=0.011), and end-exercise Tre during exercise-heat-stress (−0.47°C; p=0.042). Despite a similar endogenous thermal stimulus to HWI, EHA elicited a modest reduction in end-exercise Tre (−0.26°C), which was not different from TNE (−0.25°C, p=1.000). There were no main effects or interaction effects for end-exercise Tsk, heart rate, physiological strain index, RPE, thermal sensation, plasma volume, or TTE (all p≥0.154).ConclusionCompared with conventional short-term exercise heat acclimation, short-term post-exercise hot water immersion elicited larger thermal adaptations.

AB - ObjectivesTo compare heat acclimation adaptations after three and six days of either post-exercise hot water immersion (HWI) or exercise-heat-acclimation (EHA) in recreationally active individuals.DesignRandomised, mixed model, repeated measures.MethodsPost-exercise HWI involved a daily 40-min treadmill-run at 65% V̇O2peak in temperate conditions (19°C, 45% RH) followed by HWI (≤ 40 min, 40°C water; n=9). Daily EHA involved a ≤60-min treadmill-run in the heat (65% V̇O2peak; 33°C, 40% RH; n=9), chosen to elicit a similar endogenous thermal stimulus to HWI. A thermoneutral exercise intervention (TNE, 19°C, 45% RH; n=9), work-matched to EHA, was also included to determine thermoregulatory adaptations to daily exercise in temperate conditions. An exercise heat-stress-test was performed before and after three and six intervention days and involved a 40-min treadmill-run and time-to-exhaustion (TTE) at 65% V̇O2peak in the heat (33°C, 40% RH).ResultsANCOVA, using baseline values as the covariate, revealed no interaction effects but significant group effects demonstrated that compared to EHA, HWI elicited larger reductions in resting rectal temperature (Tre; p=0.021), Tre at sweating onset (p=0.011), and end-exercise Tre during exercise-heat-stress (−0.47°C; p=0.042). Despite a similar endogenous thermal stimulus to HWI, EHA elicited a modest reduction in end-exercise Tre (−0.26°C), which was not different from TNE (−0.25°C, p=1.000). There were no main effects or interaction effects for end-exercise Tsk, heart rate, physiological strain index, RPE, thermal sensation, plasma volume, or TTE (all p≥0.154).ConclusionCompared with conventional short-term exercise heat acclimation, short-term post-exercise hot water immersion elicited larger thermal adaptations.

KW - Acclimatisation

KW - endurance training

KW - thermotolerance

KW - performance

KW - Hot Bath

KW - running

U2 - 10.1016/j.jsams.2021.05.008

DO - 10.1016/j.jsams.2021.05.008

M3 - Article

VL - 24

SP - 729

EP - 734

JO - Journal of Science and Medicine in Sport

JF - Journal of Science and Medicine in Sport

SN - 1440-2440

IS - 8

ER -