Individual characteristics associated with the magnitude of heat acclimation adaptations

Abstract

Purpose The 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. Methods Twenty-four participants (9 female, 15 male; maximum oxygen uptake [$$\dot{{V}}$$ 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). Results Body dimensions (p > 0.3) and $$\dot{{V}}$$ 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). $$\dot{{V}}$$ V ˙ O2peak,kg did not differ among levels of responsiveness for WBSR and HR (p > 0.3). Conclusion Individual body dimensions influenced the magnitude of sudomotor and cardiovascular adaptive responses, but did not differentiate Tre adaptations to HA. The influence of $$\dot{{V}}$$ V ˙ O2peak,kg on the magnitude of adaptations was limited.

A crossover control study of three methods of heat acclimation on the magnitude and kinetics of adaptation

“…Large observed variability in PVE -both between and within individuals -is common in short term HA studies, where the variation in the response can equal the magnitude of the average change (Garrett et al, 2012(Garrett et al, , 2014Graham et al, 2016;Pethick et al, 2018;Racinais et al, 2012;Willmott et al, 2017). Individual factors such as fitness, baseline Hct, previous heat exposure and body dimensions may partly explain variation in the PVE response (Alkemade et al, 2021;Corbett et al, 2018). However, the modulating factors of individual variation to HA are still largely unresolved (Corbett et al, 2018), particularly in designs conducive to such conclusions (Atkinson & Batterham, 2015;Atkinson et al, 2019).…”

Effects of Acute Heat and Cold Exposures at Rest or during Exercise on Subsequent Energy Intake: A Systematic Review and Meta-Analysis

“…Energy intake is an outcome subject to a high degree of interindividual variability [44][45][46]. As thermal stress is also experienced very differently between individuals [47][48][49] and physiological and perceptive markers may be very weakly associated [50,51], we expected to find inconsistent effects of heat and cold exposures on energy intake. However, despite all these limitations, we found that exposures to heat and cold had clear effects, as the changes in energy intake were small-to-modest but appear robust under the circumstances.…”

Short-term heat acclimation preserves knee extensor torque but does not improve 20 km self-paced cycling performance in the heat

“…The precise reason for the observed inter-individual variability in response to HA is difficult to determine. It could relate to an individualised genetic or phenotypic characteristics that modulate the magnitude of the response to HA adaptation (Taylor 2014 ; Corbett et al 2018 ; Alkemade et al 2021 ). Conceivably, some athletes or coaches may consider short-term HA training an acceptable risk to obtain a possible performance advantage.…”