Responses of menstrual women, amenorrheal women, and men to exercise in a hot, dry environment.

Rectal (Tre) and mean skin temperatures, heart rate (fc) and sweat rate (Msw) during exercise in a hot, dry environment were compared among four menstrual women (both before and after ovulation), four amenorrheal women and four men, all with similar aerobic capacities. Progesterone and estrogen were compared in a pair of monozygotic twins (one menstrual and one amenorrheal) who participated in the study. Before acclimation, subjects were given a heat-stress test (HST) consisting of treadmill walking at 25%-30% VO2 max in a hot, dry environment (Tdb/Twb = 48/25 degrees C) until Tre reached 39 degrees C or fc reached 160 beat . min-1. Subjects were then acclimated to the dry heat with conventional acclimation procedures. After acclimation, subjects were given a HST which continued for 3 h. Before acclimation Tre and fc increased more rapidly in the women, with the men. Following acclimation all subjects maintained similar Tre, fc, and sweat rates. There were no differences between the exercise/heat-stress responses of the preovulatory menstrual women, postovulatory menstrual women, and amenorrheal women. Although the estrogen concentrations were normal in the menstrual twin, her progesterone concentrations were significantly depressed. Both hormones were depressed in the amenorrheal twin. Following acclimation thermoregulatory function in dry heat did not differ between the sexes when fitness level was similar. Neither were there any differences in thermoregulation between the pre- and postovulatory phases of the menstrual cycle or between the menstrual and amenorrheal women.