Individual characteristics associated with the magnitude of heat acclimation adaptations

Puck Alkemade,Nicola Gerrett,Thijs M H Eijsvogels,Hein A M Daanen

doi:10.1007/s00421-021-04626-3

Abstract

PurposeThe magnitude of heat acclimation (HA) adaptations varies largely among individuals, but it remains unclear what factors influence this variability. This study compared individual characteristics related to fitness status and body dimensions of low-, medium-, and high responders to HA.MethodsTwenty-four participants (9 female, 15 male; maximum oxygen uptake [dot{{V}}O2peak,kg] 52 ± 9 mL kg−1 min−1) completed 10 daily controlled-hyperthermia HA sessions. Adaptations were evaluated by heat stress tests (HST; 35 min cycling 1.5 W kg−1; 33 °C, 65% relative humidity) pre- and post-HA. Low-, medium-, and high responder groups were determined based on tertiles (n = 8) of individual adaptations for resting rectal temperature (Tre), exercise-induced Tre rise (ΔTre), whole-body sweat rate (WBSR), and heart rate (HR).ResultsBody dimensions (p > 0.3) and dot{{V}}O2peak,kg (p > 0.052) did not differentiate low-, medium-, and high responders for resting Tre or ΔTre. High WBSR responders had a larger body mass and lower body surface area-to-mass ratio than low responders (83.0 ± 9.3 vs 67.5 ± 7.3 kg; 249 ± 12 vs 274 ± 15 cm2 kg−1, respectively; p < 0.005). Conversely, high HR responders had a smaller body mass than low responders (69.2 ± 6.8 vs 83.4 ± 9.4 kg; p = 0.02). dot{{V}}O2peak,kg did not differ among levels of responsiveness for WBSR and HR (p > 0.3).ConclusionIndividual body dimensions influenced the magnitude of sudomotor and cardiovascular adaptive responses, but did not differentiate Tre adaptations to HA. The influence of dot{{V}}O2peak,kg on the magnitude of adaptations was limited.

Highlights

Heat acclimation (HA), i.e., repeated exposures to heat stress within a certain time frame, can be adopted to artificially induce improvements in sweat and skin blood flow responses, fluid balance, cardiovascular stability, and thermal tolerance. These adaptive responses result in a lower thermal strain during exercise at a given workload, which is usually reflected by a lower core temperature, heart rate (HR) and skin temperature, higher whole-body sweat rate (WBSR), and improved thermal comfort (Periard et al 2015; Daanen et al 2018)
HA was performed with a power output of 91 ± 18 W, HR of 132 ± 14 bpm, and WBSR of 1244 ± 444 g h−1
Our findings suggest that high WBSR responders generally had a large body mass and body surface area (BSA) and low BSA-to-mass ratio, whereas high HR responders typically had a small body mass and BSA

Summary

Introduction

Heat acclimation (HA), i.e., repeated exposures to heat stress within a certain time frame, can be adopted to artificially induce improvements in sweat and skin blood flow responses, fluid balance, cardiovascular stability, and thermal tolerance. These adaptive responses result in a lower thermal strain during exercise at a given workload, which is usually reflected by a lower core temperature, heart rate (HR) and skin temperature, higher whole-body sweat rate (WBSR), and improved thermal comfort (Periard et al 2015; Daanen et al 2018). There is potentially a genetic component that mediates HA responsiveness (Bouchard et al 2011; Taylor 2014), but phenotypic characteristics such as fitness status and body dimensions may relate to inter-individual differences in the adaptive response to HA (Pandolf et al 1977; Taylor 2014; Casadio et al 2017; Corbett et al 2018)

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