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Clinical Trial
. 2022 May 25;19(11):6412.
doi: 10.3390/ijerph19116412.

Effects of Heat Acclimation Following Heat Acclimatization on Whole Body Heat Exchange in Trained Endurance Athletes

Yasuki Sekiguchi  1   2 , Courteney L Benjamin  1   3 , Elaine C Lee  4 , Jeb F Struder  1 , Ciara N Manning  1 , Margaret C Morrissey  1 , Michael R Szymanski  1 , Rebecca L Stearns  1 , Lawrence E Armstrong  4 , Douglas J Casa  1
Affiliations
Clinical Trial

Effects of Heat Acclimation Following Heat Acclimatization on Whole Body Heat Exchange in Trained Endurance Athletes

Yasuki Sekiguchi et al. Int J Environ Res Public Health. .

Abstract

The purpose of this study was to examine the changes in metabolic heat production (Hprod), evaporative heat loss (Hevap), and dry heat loss (Hdry), following heat acclimatization (HAz) and heat acclimation (HA). Twenty-two male endurance athletes (mean ± standard deviation; age, 37 ± 12 y; body mass, 73.4 ± 8.7 kg; height, 178.7 ± 6.8 cm; and VO2max, 57.1 ± 7.2 mL·kg−1·min−1) completed three trials (baseline; post-HAz; and post-HA), which consisted of 60 min steady state exercise at 59 ± 2% velocityVO2max in the heat (ambient temperature [Tamb], 35.2 ± 0.6 °C; relative humidity [%rh] 47.5 ± 0.4%). During the trial, VO2 and RER were collected to calculate Hprod, Hevap, and Hdry. Following the baseline trial, participants completed self-directed outdoor summer training followed by a post-HAz trial. Then, five days of HA were completed over eight days in the heat (Tamb, 38.7 ± 1.1 °C; %rh, 51.2 ± 2.3%). During the HA sessions, participants exercised to maintain hyperthermia (38.50 °C and 39.75 °C) for 60 min. Then, a post-HA trial was performed. There were no differences in Hprod between the baseline (459 ± 59 W·m−2), post-HAz (460 ± 61 W·m−2), and post-HA (464 ± 55 W·m−2, p = 0.866). However, Hevap was significantly increased post-HA (385 ± 84 W·m−2) compared to post-HAz (342 ± 86 W·m−2, p = 0.043) and the baseline (332 ± 77 W·m−2, p = 0.037). Additionally, Hdry was significantly lower at post-HAz (125 ± 8 W·m−2, p = 0.013) and post-HA (121 ± 10 W·m−2, p < 0.001) compared to the baseline (128 ± 7 W·m−2). Hdry at post-HA was also lower than post-HAz (p = 0.049). Hprod did not change following HAz and HA. While Hdry was decreased following HA, the decrease in Hdry was smaller than the increases in Hevap. Adaptations in body heat exchange can occur by HA following HAz.

Keywords: dry heat loss; evaporation; heat adaptations; heat balance; metabolic heat production; running economy.

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Conflict of interest statement

The authors declare no conflict of interests.

Figures

Figure 1
Figure 1
Changes in metabolic heat production following heat acclimatization and acclimation. Baseline indicates unacclimatized, Post-HAz indicates post-heat acclimatization, Post-HA indicates post-heat acclimation.
Figure 2
Figure 2
Changes in evaporative heat loss following heat acclimatization and acclimation. * indicates statistical significance following heat acclimation (Post-HA), p ≤ 0.05. Baseline indicates unacclimatized, Post-HAz indicates post-heat acclimatization, Post-HA indicated post-heat acclimation.
Figure 3
Figure 3
Changes in dry heat loss following heat acclimatization and acclimation. * indicates statistical significance following heat acclimation (Post-HA), and + indicates statistical significance following heat acclimatization (Post-HAz), p ≤ 0.05. Baseline indicates unacclimatized, Post-HAz indicates post-heat acclimatization, Post-HA indicates post-heat acclimation.
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