Thermoregulation in Menopausal Women Exercising in the Heat

Abstract

The activation of hyperthermic mechanisms is a result of autonomic responses that facilitate heat loss. These mechanisms are characterized as vasodilation, core to shell gradient, and sweat response. At rest, menopausal women have had adverse changes in thermoregulatory function such as hot flashes. During exercise, menopausal women have shown to be less heat tolerant resulting in higher core temperatures. PURPOSE: The study was designed to determine if differences existed in thermoregulatory mechanisms between premenopausal and menopausal women exercising in a thermoneutral and hot humid environment. METHODS: Subjects were either premenopausal (N = 5) or menopausal (N = 5) who exercised on a motorized treadmill at 65% O2peak for a maximum of 60 min. Thermoregulatory data were collected during two different sessions. The variables evaluated were heart rate, respiratory exchange ratio, core temperature, mean skin temperature, mean body temperature, rate of perceived exertion, thermal sensation, plasma volume shifts, hematocrit, blood volume, pre-exercise and post-exercise nude body weight, clothing weight, towel weight, sweat rate, heat storage, evaporation, radiation, and convection. RESULTS: Nineteen mixed factorial ANOVAs were computed to determine if significant interactions existed. A significant (p <.05) interaction was observed between subjects for core temperatures in the hot humid environment. Menopausal women had significantly higher core body temperature in the first (38.03°C) and second (38.52°C) time frame in the hot humid environment. No differences between the two groups were reported during the thermoneutral environment for core body temperature. No significant (p >.05) interactions were observed for any other thermoregulatory variables between groups. CONCLUSION: Menopausal women had higher core temperatures in the first two-thirds of the exercise bout in the hot humid environment. Evaporative heat loss was compromised in the hot humid environment. This caused a greater increase in heat storage in menopause women possibility causing core temperatures to remain high. These results provide some evidence to the adverse changes in thermoregulatory functioning of menopausal women.