Gender differences in physiological reactions to thermal stress

Following an extensive anthropometric evaluation, thermoregulatory responses were studied in nine men and nine women who performed immersed exercise with post-exercise rest in 28°C water. During the post-exercise period esophageal temperature (T _es), oxygen consumption, heat flux and skin blood perfusion were monitored at 10s intervals, with average minute values used for calculations. The T _es (relative to restingT _es) at which sweating abated and shivering commenced were defined as the T _es thresholds for the cessation of sweating and onset of shivering, respectively. No significant gender differences were evident in the sweating and shivering threshold T _es values, or the magnitude of the null-zone. Usingz-tests for parallelism the rates of core cooling across the null-zone were not found to differ significantly between genders, nor were the slopes of the perfusion: T _es responses across the null-zone or the post-threshold shivering responses (ml·kg^–1·min^–1·°C^–1). The slope of the sweating response (measured from immersion until sweat cessation; g·m^–2·min^–1°C^–1) was, however, significantly lower in the female than in the male samples (z = 3.93;P < 0.01). Despite the gender-related dimorphic distribution of adipose tissue, both men and women lost equal proportions of their total heat flux from central and peripheral measurement sites. Performing a standardized regression using the rate of core cooling across the null-zone as the dependent variable and gender as a dummy variable, gender and adipose tissue mass were not found to be significant factors in determining the rate of core cooling, while mass ( = 1.73;P < 0.05) and muscle mass ( = 1.86;P < 0.05) did contribute significantly to the rate of core cooling. It was concluded that, except for the quantitative differences in the sweating response, men and women respond to deviations in core temperature in a similar manner, with mass and muscle mass modifying this response.