What question did this study set out to answer?

To investigate the impact of body mass index on physiological adaptations during heat acclimation in healthy adults.

January 20, 2026Open Access

Inter‐individual variability in physiological adaptations during heat acclimation in adults: Contributions of body mass index and body size

SBShaun C. BrazeltonU.S. Army Research Institute of Environmental Medicine NCNisha CharkoudianU.S. Army Research Institute of Environmental Medicine KBKarleigh E. BradburyU.S. Army Research Institute of Environmental Medicine

Key Points

To investigate the impact of body mass index on physiological adaptations during heat acclimation in healthy adults.
Forty-two healthy adults participated in a heat acclimation protocol for 8 days.
Participants performed treadmill walking at 40°C and 40% relative humidity.
Measurements included core temperature, heart rate, and whole-body sweating rate at specified intervals.
Individuals with BMI <25 exhibited significant decreases in peak core temperature over the acclimation period.
The BMI >25 group only showed a decrease in peak core temperature on the final day of testing.
Differences in peak core temperature between groups were significant on Day 8, with the BMI <25 group showing greater adaptations.

Abstract

Abstract Heat acclimation refers to the physiological adaptations that occur during repeated heat exposures, ultimately reducing thermal and cardiovascular strain in the heat. It is unknown whether body mass index (BMI) influences an individual's ability to adapt during heat acclimation, which was tested in the present analysis. Forty‐two healthy adults (16F; age: 23 ± 5 years) underwent 8 days of treadmill walking (5 km·h −1 ) in the heat (40°C, 40% RH). Groups were compared based on BMI (25). We measured core temperature (T C ), heart rate (HR) and whole‐body sweating rate (WBSR) on days 1, 4 and 8. The BMI 25 group showed a reduction in peak T C only on Day 8 (38.35 ± 0.45) compared to Day 1 (38.54 ± 0.53, p = 0.019). Peak T C was lower in the BMI 25 group on Day 8 only ( p = 0.042). HR decreased and WBSR increased over time, with no difference between groups ( p > 0.05). The BMI 25 group ( p = 0.010). These data suggest that individuals with BMI >25 may have attenuated T C adaptations to heat acclimation compared to individuals with BMI <25.

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