The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis

Abstract

HA regimens lasting <14 days induce many beneficial physiological and perceptual adaptations to high ambient temperatures, and improve subsequent exercise performance and capacity in the heat; however, the extent of the adaptations is greatest when HA regimens lasting longer than 14 days are adopted. Large methodological differences in the HA literature mean that there is still uncertainty regarding the magnitude and time course of potential adaptation for a number of physiological and perceptual variables.

Short-term, low-volume training improves heat acclimatization in an operational context

“…There was no difference between the two groups, although urine osmolality increased between D7 and D1. Then, the training sessions in the present study was shorter (32-54 min) than those (78 min) used in short-term heat acclimation protocols (Tyler et al, 2016). Mean intensity is difficult to determine because depending on studies intensities are sometimes based on a speed, slope, or power and sometimes on relative intensity.…”

“…The comparison of published work with the present study may have limitations (differences in the type of acclimation, population, and volume of training). However, the kinetics of published studies (Périard et al, 2015;Tyler et al, 2016) were almost perfectly respected: HR and rectal temperatures decreased after only 7 days (between −7.6 and −11.8% and between −0.36 and −0.97%, in the NT and T groups, respectively) and thermal discomfort greatly improved (between 15.5 and 54.3%) for all participants. Sweat loss decreased slightly (−15.5%) after 7 days, suggesting that the sweat glands were not yet able to produce more sweat in the conditions of the present study.…”

“…Reviews and meta-analyses (Taylor, 2014;Périard et al, 2015;Tyler et al, 2016) provide a precise summary of the overall kinetics of heat acclimation-induced physiological changes. After 7 days, as in the present study (i.e., 2 days of HST and 5 days of training), the maximal heat acclimation-induced improvements are almost already obtained, including HR, core temperature, and thermal comfort (Périard et al, 2015).…”

“…This problem was recognized more than 200 years ago when Europeans arriving in tropical climates did not adapt their working behaviors and eventually faced heat illnesses (Lind, 1771;Jackson, 1795;Taylor, 2014). Heat acclimation (or more accurately heat acclimatization as heat stress is produced by the environment and not simulated in thermal rooms) alleviates these losses in performance by producing physiological changes that reduce the deleterious effects of heat stress (Périard et al, 2015;Tyler et al, 2016). For more details, Taylor (2014) accurately reports the functional modifications that occur during heat acclimation.…”

“…Indeed, passive heat acclimatization is less efficient than active heat acclimatization by work-induced physical activity (Horvath and Shelley, 1946;Hellon et al, 1956;Joy et al, 1964;Pandolf et al, 1977) or training sessions (Périard et al, 2015(Périard et al, , 2016Racinais et al, 2015;Tyler et al, 2016). To be effective, in terms of heat acclimation-induced physiological modifications, an exercise session performed in the heat should trigger high sweat rates and largely increase core body temperature (Henane et al, 1977;Racinais et al, 2015).…”