Hypohydration and exercise: effects of heat acclimation, gender, and environment

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Abstract
The effects of heat acclimation and subject gender on treadmill exercise in comfortable (20.degree. C, 40% rh [relative humidity]), hot-dry (49.degree. C, 20% rh) and hot-wet (35.degree. C, 79% rh) environments while subjects were hypo- or euhydrated were studied. Six male and 6 female subjects, matched for maximal aerobic power and percent body fat, completed 2 exercise tests in each environment both before and after a 10-day heat acclimation program. One exercise test was completed during euhydration and one during hypohydration (-5.0% from baseline body weight). In general, no significant (P > 0.05) differences were noted between men and women at the completion of exercise for rectal temperature (Tre), mean skin temperature (.hivin.Tsk) or heat rate (HR) during any of the experimental conditions. Hypohydration generally increased Tre and HR values and decreased sweat rate values while not altering .hivin.Tsk values. In the hypohdyration experiments, heat acclimation significantly reduced Tre (0.19.degree. C) and HR (13 beats .cntdot. min-1) values in the comfortable environment, but only HR values were reduced in hot-dry (21 beats .cntdot. min-1) and hot-water (21 beats .cntdot. min-1) environments. Men and women evidently respond in a physiologically similar manner to hypohydration during exercise. For hypohydrated subjects heat acclimation evidently decreased thermoregulatory and cardiovascular strain in a comfortable environment, but only cardiovascular strain decreased in hot environments.