Effects of body composition and menstrual cycle on thermoregulation of women

Abstract

Purpose. The purpose of this study was to examine thermoregulatory responses during three phases of the menstrual cycle in high fat and low fat women while exercising. Procedure. Subjects who volunteered for the study underwent screening procedures to determine fitness level, percent body fat, and appropriateness to the study regarding their menstrual cycle. Qualifying subjects (N = 20) were assigned to high and low fat groups based on their percent body fat, and randomly assigned to either the experimental or control group. The experimental group was exposed to 35(DEGREES)C heat during each of three exercise sessions, while the control group experienced a neutral temperature (24(DEGREES)C). The three exercise sessions occurred during the menstrual, preovulatory, and postovulatory phases of the menstrual cycle. During these sessions, subjects pedalled a cycle ergometer for 30 min while core temperature, skin temperature, local sweat rate on the back, heart rate, and forearm blood flow were monitored and recorded every 3 min. Nude weight was obtained before and after each exercise session to determine total body sweat rate. Hemoglobin and hematocrit values were determined prior to each exercise session. Core temperature, mean skin temperature, local sweat rate, and heart rate were analyzed separately using a four factor factorial analysis of variance design, with repeated measures on cycle phase and time into the work bout. A three factor factorial analysis of variance with repeated measures on cycle phase was used for analyzing hemoglobin, hematocrit, and total body sweat rate. Forearm blood flow was discussed in relationship to these analyses. Results. Examination of the analysis of variance and simple main effects led to the following conclusions: (1) The menstrual cycle affects thermoregulation, as seen in elevated mean skin temperature during the menstrual phase and lower resting sweat rate during the preovulatory and postovulatory phases. (2) Body composition has little effect on thermoregulatory responses due to high ambient temperature or exercise. (3) Exercise in the heat requires thermoregulatory responses in order to maintain the body's core temperature.