Heat acclimation is the best strategy to improve performance in a hot environment. Many athletes seeking the benefits of heat acclimation lack access to a hot environment for exercise and, thus, rely on overdressing to simulate environmental heat stress. It is currently unknown whether this approach produces the requisite thermoregulatory strain necessary for heat acclimation in trained men and women. Purpose To compare physiological and cellular responses to exercise in a hot environment (HOT; 40°C, 30% RH) with minimal clothing (clo = 0.87) and in a temperate environment (CLO; 15°C, 50% RH) with overdressing (clo = 1.89) in both men and women. Methods HR, rectal temperature (T re), mean skin temperature (T sk), sweating rate (SR), and extracellular heat shock protein (eHSP)72 were measured in 13 (7 males, 6 females) well-trained runners (V.O2max: 58.7 ± 10.7 mL/kg·min) in response to ~60 min of treadmill running at 50%-60% V.O2max in HOT and CLO. Results T re increased in both conditions, but the increase was greater in HOT (deltaT re HOT: 2.6°C ± 0.1°C; CLO 2.0°C ± 0.1°C; P = 0.0003). SR was also higher in HOT (1.41 ± 0.1 L h-1; CLO: 1.16 ± 0.1 L/h; P = 0.0001). eHSP72 increased in HOT (% change: 59% ± 11%; P = 0.03) but not in CLO (6% ± 2%; P = 0.31). Mean T sk and HR were not different between HOT and CLO in men but were higher in HOT for women. Conclusion These data support the idea that overdressing during exercise in a temperate environment may produce the high T re, T sk, HR, and SR necessary for adaptation, but these responses do not match those in hot, dry environments. It is possible that greater exercise stimulus, warmer environment, or more clothing may be required to allow for a similar level of acclimation.
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