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 degrees C water. During the post-exercise period esophageal temperature (Tes), oxygen consumption, heat flux and skin blood perfusion were monitored at 10 s intervals, with average minute values used for calculations. The delta Tes (relative to resting Tes) at which sweating abated and shivering commenced were defined as the delta Tes thresholds for the cessation of sweating and onset of shivering, respectively. No significant gender differences were evident in the sweating and shivering threshold delta Tes values, or the magnitude of the null-zone. Using z-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: delta Tes responses across the null-zone or the post-threshold shivering responses (ml.kg-1.min-1.degrees C-1). The slope of the sweating response (measured from immersion until sweat cessation; g.m-2.min-1 degree 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.(ABSTRACT TRUNCATED AT 250 WORDS)