Heat Acclimation Following Heat Acclimatization Elicits Additional Physiological Improvements in Male Endurance Athletes.

Courteney L Benjamin,Ciara N Manning,Yasuki Sekiguchi,Robert A Huggins,Douglas J Casa,Andrew J Grundstein,Jeb F Struder,Michael R Szymanski,Lawrence E Armstrong,Elaine C Lee

doi:10.3390/ijerph18084366

Abstract

The purpose of this study was to assess the effectiveness of heat acclimatization (HAz) followed by heat acclimation (HA) on physiological adaptations. 25 male endurance athletes (age 36 ± 12 y, height 178.8 ± 6.39 cm, body mass 73.03 ± 8.97 kg, and VO2peak 57.5 ± 7.0 mL·kg−1·min−1) completed HAz and HA. HAz was 3 months of self-directed summer training. In the laboratory, a 5-day HA prescribed exercise to target a hyperthermic zone (HZHA) of Trec between 38.50 and 39.75 °C for 60 min. Exercise trials were 60 min of running (59% ± 2% VO2peak) in an environmental chamber (wet bulb globe temperature 29.53 ± 0.63 °C) and administered at: baseline, post-HAz, and post-HAz+HA. Measured variables included internal body temperature (Trec), heart rate (HR), and sweat rate (SR). Repeated measure ANOVAs and post hoc comparisons were used to assess statistically significant (p < 0.05) differences. Trec was lower post-HAz+HA (38.03 ± 0.39 °C) than post-HAz (38.25 ± 0.42 °C, p = 0.009) and baseline (38.29 ± 0.37 °C, p = 0.005). There were no differences between baseline and post-HAz (p = 0.479) in Trec. HR was lower post-HAz (143 ± 12 bpm, p = 0.002) and post-HAz+HA (134 ± 11 bpm, p < 0.001) than baseline (138 ± 14 bpm). HR was lower post-HAz+HA than post-HAz (p = 0.013). SR was higher post-HAz+HA (1.93 ± 0.47 L·h−1) than post-HAz (1.76 ± 0.43 L·h−1, p = 0.027). Combination HAz and HA increased physiological outcomes above HAz. This method can be used to improve performance and safety in addition to HAz alone.

Highlights

Athletes from around the world travel to compete in hot weather conditions of which they are not accustomed to [1]
One solution to this problem is the use of heat acclimation (HA), which is the systematic process of repeated exposures to a thermally extreme environment that elicits positive physiological and perceptual adaptations [3] in an artificial environment
Athletes and coaches who live and train in milder summer climates may be under the impression that they have been completing Heat acclimatization (HAz) and are ready to compete in a hot environment, when the thermal strain of their training was not enough to elicit the physiological adaptations that are needed in a more extreme climate

Summary

Introduction

Athletes from around the world travel to compete in hot weather conditions of which they are not accustomed to [1]. Regional differences in environmental conditions, such as the mild summers experienced by many across the globe, make it difficult for athletes who are traveling to hotter venues to gain the full benefits of HAz needed prior to competition [2]. One solution to this problem is the use of heat acclimation (HA), which is the systematic process of repeated exposures to a thermally extreme environment that elicits positive physiological and perceptual adaptations [3] in an artificial environment. Typical responses following HA include lower heart rate (HR), internal body temperature, skin

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