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

Int J Environ Res Public Health. 2022 May 25;19(11):6412. doi: 10.3390/ijerph19116412.

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.

Publication types

  • Clinical Trial

MeSH terms

  • Acclimatization
  • Adult
  • Athletes
  • Body Temperature Regulation
  • Cytochrome P-450 CYP2B1*
  • Exercise
  • Hot Temperature*
  • Humans
  • Male
  • Middle Aged
  • Sweating

Substances

  • Cytochrome P-450 CYP2B1

Grant support

This research received no external funding.