The effect of seasonal acclimatization on whole body heat loss response during exercise in a hot humid environment with different air velocity

Tze Huan Lei, Masashi Fujiwara, Nicola Gerrett, Tatsuro Amano, Toby Mundel, Yoshimitsu Inoue, Dai Okushima, Takeshi Nishiyasu, Narihiko Kondo*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Seasonal acclimatization from winter to summer is known to enhance thermoeffector responses in hot-dry environments during exercise whereas its impact on sweat evaporation and core temperature (Tcore) responses in hot-humid environments remains unknown. We, therefore, sought to determine whether seasonal acclimatization is able to modulate whole body sweat rate (WBSR), evaporated sweat rate, sweating efficiency, and thermoregulatory function during cycling exercise in a hot-humid environment (32 °C, 75% RH). We also determined whether the increase in air velocity could enhance evaporated sweat rate and sweating efficiency before and after seasonal acclimatization. Twelve males cycled for 1 h at 40% V-O2max in winter (preacclimatization) and repeated the trial again in summer (after acclimatization). For the last 20 min of cycling at a steady-state of Tcore, air velocity increased from 0.2 (0.04) m/s to 1.1 (0.02) m/s by using an electric fan located in front of the participant. Seasonal acclimatization enhanced WBSR, unevaporated sweat rate, local sweat rate and mean skin temperature compared with preacclimatization state (all P < 0.05) whereas sweating efficiency was lower (P < 0.01) until 55 min of exercise. Tcore and evaporated sweat rate were unaltered by acclimatization status (all P > 0.70). In conclusion, seasonal acclimatization enhances thermoeffector responses but does not attenuate Tcore during exercise in a hot-humid environment. Furthermore, increasing air velocity enhances evaporated sweat rate and sweating efficiency irrespective of acclimated state. NEW & NOTEWORTHY Seasonal acclimatization to humid heat enhances eccrine sweat gland function and thus results in a higher local and whole body sweat rate but does not attenuate Tcore during exercise in a hot-humid environment. Sweating efficiency is lower after seasonal acclimatization to humid heat compared with preacclimatization with and without the increase of air velocity. However, having a lower sweating efficiency does not mitigate the Tcore response during exercise in a hot-humid environment.

Original languageEnglish
Pages (from-to)520-531
Number of pages12
JournalJournal of Applied Physiology
Volume131
Issue number2
Early online date5 Aug 2021
DOIs
Publication statusPublished - Aug 2021

Bibliographical note

Funding Information:
This study was supported by a Grant in Aid for Scientific Research (P18793) from the Japan Society for the Promotion of Science from the Ministry of Education.

Publisher Copyright:
Copyright © 2021 the American Physiological Society.

Funding

This study was supported by a Grant in Aid for Scientific Research (P18793) from the Japan Society for the Promotion of Science from the Ministry of Education.

FundersFunder number
Japan Society for the Promotion of Science
Ministry of Education

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