Four-month operational heat acclimatization positively affects the level of heat tolerance 6 months later

Benefits gained after heat acclimation or acclimatization are typically thought to be completely lost after about 6 weeks, but this estimate is hypothetical. We evaluated the long-term effects of heat acclimatization on heat tolerance. Physiological and subjective markers of heat tolerance were assessed during a heat stress test (HST: three 8-min outdoor runs at approximately 40 °C and 20% relative humidity at 50% of estimated speed at VO2max) performed on the second day upon arrival at a desert military base in the United Arab Emirates after a first day of mostly passive heat exposure. Among 50 male French soldiers, 25 had performed a 4-month military mission in hot climates 6 months prior (HA) and 25 had never been heat acclimatized (CT). Rectal temperature (p = 0.023), heart rate (p = 0.033), and perceived exertion (p = 0.043) were lower in HA than CT at the end of the HST. Soldiers with a previous 4-month period of natural heat acclimatization very likely had higher heat tolerance during exercise in the heat, even 6 months after returning from a desert mission, than non-acclimatized counterparts.

Alexandra Malgoyre, Julien Siracusa, Pierre-Emmanuel Tardo-Dino, Sebastian Garcia-Vicencio, Nathalie Koulmann, Yoram Epstein, Keyne Charlot