Physiological responses of physically fit men and women to acclimation to humid heat

Abstract

Four men and 4 women with comparable maximal aerobic capacities (64.2 and 65.7 ml/kg LBM [lean body mass] per min, respectively) and equal surface areas and surface area-to-mass ratios underwent a 3 h heat stress test (Tdb (dry bulb temperature) = 36.degree. C; Twb (wet bulb temperature) = 30.degree. C; .ovrhdot.VO2 [oxygen consumption] = 1.01/min) before and after a 10-day acclimation to humid heat (Tdb = 36.degree. C; Twb = 32.degree. C). Women were tested during both pre- and postovulation (pre-OV, post-OV). Prior to acclimation, pre-OV women exhibited the longest tolerance times and lowest rectal temperatures (Tre) and heart rates (HR) throughout testing. Men secreted considerably more sweat per unit area than did women in either phase of the cycle, yet they demonstrated shorter tolerance times and higher body temperatures and HR. During post-OV, women reacted similarly to men except that their sweat rates and HR values were significantly lower. Following acclimation, the Tre and HR of the men and women were similar, whereas the discrepancy between the sweat rates was magnified. Aerobic capacity is an important factor to be considered when men and women are compared in the heat. When fitness levels are similar, the previously reported sex-related differences in response to an acute heat exposure seem to disappear, except for the higher sweat rate for men.