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

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