Whether BMI influences the amount of heat adaptation gained throughout a heat training block; and,
Whether BMI is related to the amount of exercise-induced core temperature increase in both a heat adapted and an unadapted state.
The hypothesis was that because individuals with a higher BMI are at a greater risk for heat-related illness, those individuals would have greater thermal stress during exercise and thus greater adaptation.
The protocol was an 8-day heat training block.
Key Findings
For the group with BMI <25:
Their peak core temperature during exercise was lower on day 4 than on day 1. It lowered further still by day 8.
On day 8, their peak core temp was lower than the peak core temp of those with BMI>25
From day 1 to day 8, their reduction in peak core temp was greater than the reduction in those with BMI >25.
For the group with BMI >25:
Their peak core temp during exercise did not lower until day 8.
TAKEAWAYS:
On day 1, there was no correlation between BMI and peak core temperature. On day 8, there was significant correlation (higher BMI correlated to higher core temperature).
Healthy young adults with a BMI >25 experienced less heat adaptation in the 8-day heat training block when compared to individuals with a BMI <25. This was opposite the researchers’ hypothesis.
Methodologies
42 United States Army personnel (26 men, 16 women) were split into two groups: those with a BMI <25 and those with a BMI >25.
Both groups completed 8 days of treadmill walking in a hot climate chamber (40°C/104°F, 40% relative humidity) for 120 minutes each day.
Core and skin temperature, heart rate, and sweat rate were measured.
CORE's Hot Take
Many workplaces and militaries use standardized heat adaptation protocols. Results of this study suggest that individuals with a higher BMI may benefit from a longer heat adaptation protocol than is used for those with a lower BMI.
Many heat adaptation protocols use 14 days to see full adaptations. It is unknown if the higher BMI individuals would have reached the same level of adaptation as the lower BMI individuals if the protocol had been extended from 8 to 14 days. We estimate that the 8-day protocol would yield a CORE Heat Adaptation Score of 80–90%.
BMI may be an efficient and effective way for organizations to prescribe individualized heat adaptation protocols for their members.
Moving Forward
This study gives important information to organizations designing heat adaptation protocols. It also raises questions for future research:
Would higher BMI individuals reach equal heat adaptation as the lower BMI individuals with a longer heat training block?
It is believed that individuals with lower fitness and/or higher percentage of body fat adapt to heat less quickly than individuals with higher fitness and/or lower percent of body fat. What are the causative effects of fitness, percent body fat, and BMI on heat adaptation?
CORE does not currently take into account BMI in predicting the Heat Adaptation Score. Should CORE’s metric be individualized to account for BMI?
Emerging research like this helps shape how we approach product development at CORE. BMI is just one of several indicators with the potential to inform a more personalized set of CORE metrics and insights. CORE’s research and development team are actively exploring how to bring greater individualization into future iterations of CORE products.
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