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Effectiveness of short-term isothermic-heat acclimation (4 days) on physical performance in moderately trained males

Shaw, Jake; Walkington, Cory; Cole, Edward; Gleadall-Siddall, Damien O.; Burke, Rachel; Bray, James; Simpson, Andrew J.; Vince, Rebecca V.; Garrett, Andrew T.


Jake Shaw

Cory Walkington

Edward Cole

Damien O. Gleadall-Siddall

Rachel Burke

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Dr James Bray
Lecturer in Sport Nutrition & Physiology

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Dr Andrew Garrett
Senior Lecturer in Exercise and Environmental Physiology


Introduction A typical heat acclimation (HA) protocol takes 5–7 d of 60–90 minutes of heat exposure. Identifying the minimum dose of HA required to elicit a heat adapted phenotype could reduce financial constraints on participants and aid in the tapering phase for competition in hot countries. Therefore, the aim of this study was to investigate a 4 d HA regimen on physical performance Methods Twelve moderately trained males were heat acclimated using controlled hyperthermia (Tre>38.5◦C), with no fluid intake for 90 min on 4 consecutive days, with a heat stress test (HST) being completed one week prior to (HST2), and within one-week post (HST3) HA. Eleven completed the control study of HST1 versus HST2, one week apart with no intervention. Heat stress tests comprised of cycling for 90 min @ 40% Peak Power Output (PPO); 35◦C; 60%RH followed by 10 minutes of passive recovery before an incremental test to exhaustion. Physical performance outcomes time to exhaustion (TTE), PPO, end rectal temperature (Tre END), and heart rate (HREND) was measured during the incremental test to exhaustion. Results Physiological markers indicated no significant changes in the heat; however descriptive statistics indicated mean resting Tre lowered 0.24◦C (-0.54 to 0.07◦C; d = 2.35: very large) and end-exercise lowered by 0.32◦C (-0.81 to 0.16; d = 2.39: very large). There were significant improvements across multiple timepoints following HA in perceptual measures; Rate of perceived exertion (RPE), Thermal Sensation (TS), and Thermal Comfort (TC) (P<0.05). Mean TTE in the HST increased by 142 s (323±333 to 465±235s; P = 0.04) and mean PPO by 76W (137±128 to 213±77 W; P = 0.03). Conclusion Short-term isothermic HA (4 d) was effective in enhancing performance capacity in hot and humid conditions. Regardless of the level of physiological adaptations, behavioural adaptations were sufficient to elicit improved performance and thermotolerance in hot conditions. Additional exposures may be requisite to ensure physiological adaptation.


Shaw, J., Walkington, C., Cole, E., Gleadall-Siddall, D. O., Burke, R., Bray, J., …Garrett, A. T. (2022). Effectiveness of short-term isothermic-heat acclimation (4 days) on physical performance in moderately trained males. PLoS ONE, 17(11), Article e0270093.

Journal Article Type Article
Acceptance Date Nov 4, 2022
Online Publication Date Nov 17, 2022
Publication Date Nov 17, 2022
Deposit Date Nov 29, 2022
Publicly Available Date Nov 30, 2022
Journal PLoS ONE
Print ISSN 1932-6203
Electronic ISSN 1932-6203
Publisher Public Library of Science
Peer Reviewed Peer Reviewed
Volume 17
Issue 11
Article Number e0270093
Public URL


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Copyright Statement
© 2022 Shaw et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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