Heat Stress Recommendations Do Not Prevent Core Temperature From Exceeding 38.0 °C In Adults With Obesity

Heat stress recommendations aim to prevent core temperatures (TC) from exceeding 38.0 °C in unacclimated workers. Previous work showed that adherence to the recommendations largely prevents TC from exceeding these limits in healthy adults without obesity. However, there is a high prevalence of adult workers with obesity conducting physical work in the heat. Therefore, it is essential to assess the adequacy of the heat stress recommendations in safeguarding outdoor workers with obesity. PURPOSE: To test the hypothesis that core temperature is higher in adults with obesity during simulated occupational heat stress compared to adults without obesity when adhering to the heat stress recommendations. METHODS: Sixteen unacclimated adults with (n = 5; 3 women) or without (n = 11; 5 women) obesity completed a 4-hour (half workday) exposure to a fixed WBGT and work intensity. Work-rest ratio was 30 min of walking and 30 min of seated rest each hour. Work intensity (i.e., Hprod) was prescribed as a function of WBGT (27.6 ± 0.4 °C) and normalized to body mass (5.1 ± 0.2 W/kg). All subjects were provided 237 mL of Gatorade every 15 min and drank ad libitum. Percent body fat was quantified via DXA. TC was reported over time and as peak and mean TC during the 4-hour exposure. Percent changes in body mass provided an index of hydration status. Data are presented as mean ± SD. RESULTS: Body fat % differed between groups with (37 ± 4%) and without obesity (21 ± 6%; p < 0.01). There was a time X group interaction (p < 0.01) for the change in TC during the 4-hour exposure. Mean TC differed between groups with (37.9 ± 0.2 °C) and without obesity (37.3 ± 0.3 °C; p < 0.01). Similarly, peak TC differed between groups with (38.5 ± 0.4 °C) and without obesity (37.5 ± 0.3 °C; p < 0.01). Percent change in body mass did not differ between groups with (-0.6 ± 0.7%) and without obesity (-0.5 ± 0.7%; p = 0.68). CONCLUSION: Adherence to heat stress recommendations during a 4-hour exposure resulted in elevated TC responses in adults with obesity, compared to adults without obesity, despite Hprod being prescribed relative to body mass. Consequently, the heat stress recommendations could consider adjustments to prescribe work-rest ratio or exposure limits based on body fatness, particularly given the prevalence of obesity amongst adult workers exposed to hot and/or humid environments.