Thermoregulatory responses during continuous constant load exercise in young women: differences in elevation of basal body temperature with the menstrual cycle

Abstract

A study was conducted to investigate the effects of the menstrual cycle and differences in elevation of basal body temperature (BBT) on thermoregulatory responses during continuous constant load exercise in young women. Throughout three menstrual cycles, eight healthy young women were investigated for their thermoregulatory responses during 60-min bicycle exercise at 60% Vo₂max in a normal temperature environment. The “ovulation date estimation method” established by Onoue et al. was used to validate the high-temperature phases. Based on validation of the high-temperature phases (H) and low-temperature phases (L), we categorized the results as follows: “Group I” showing more than 10 continuous days in the normal high phase, “Group II” showing a short high phase of less than 10 days, and “Group III” showing no high phase. For Groups I and II, BBT in H was significantly higher than in L (Group: p<0.001, Group: p<0.05). In Group I, the rectal temperature (Tre) in H showed an evidently higher shift than that in L at rest and during 60-min exercise (p<0.05). Also in Group II, Tre at rest in H was higher than in L (p<0.05). However, Group III without any BBT fluctuation showed no effect of the menstrual cycle on thermoregulation. Although the core temperature of L at the start of exercise was low, continuation of exercise in L tended to increase the core temperature to a regular level, as shown in H. These results suggest that thermoregulatory responses during exercise have no effect on the length of the high-temperature phase, but are affected by the difference between the BBT and the core temperature at the start of exercise.