Cognitive performance during a heat acclimatization regimen.

The cognitive performance of six male Marines undergoing a 10-d heat acclimatization regimen was assessed using repeated acquisition and time estimation tasks. Subjects performed controlled treadmill exercise in a heat acclimatization chamber at 33.3 degrees C dry bulb, 29.4 degrees C wet bulb temperature. Multiple performance assessments were conducted during each daily heat exposure of 155 min. On the first day of heat exposure, time estimates decreased from preacclimatization baseline values recorded at moderate temperatures while performance on the repeated acquisition tasks yielded slight decrements. By the 10th day of heat exposure, all subjects demonstrated significant heat acclimatization. However, mean performance on the repeated acquisition task was still impaired and time estimates were higher than during the first heat exposure. These results suggest that tasks requiring the acquisition of new behaviors may be difficult to perform in a hot environment, even by partially acclimatized individuals.