The relationship between aerobic capacity and the recruitment of activated sweat gland density with passive heating

Abstract

This study investigated whether the recruitment of activated sweat gland density during passive heating [immersion of the lower body into hot water, 41℃ for 30 min (PH), room temperature 23 ± 0.5℃ with 60 ± 3% relative humidity] is different in endurance-trained (Trainee), compared with that of untrained subjects (Control), as indicated by VO2max. Eight trainees and seven control female subjects (38.31 ± 4.91 ml․kg-1․min-1 and 31.8 ± 0.92 ml․kg-1․min-1, respectively, p < 0.01) were similar on all other physical characteristics. To compare the changes between the trainees and controls, serum cortisol and prolactin (PRL), tympanic temperature (TYMP), local activated sweat gland density (L-ASGD) and the mean whole body sweat loss volume (M-WBSLV) changes were measured after PH. The cortisol was significantly higher (p < 0.05) and the PRL tended to be higher in the Trainee than in the Control. The TYMP increased more in the Trainee than in the Control (p < 0.001). The L-ASGD showed a higher tendency in the Trainee than in the Control, there was a significant difference in the mean activated sweat gland density (p < 0.01) and the L-ASGD was significantly correlated with the VO2max (p < 0.001). The M-WBSLV was significantly higher in the Trainee (p < 0.001) and significantly correlated with the VO2max (p < 0.001). The results suggest that in humans, a high aerobic capacity is associated with a greater recruitment of activated sweat glands, whole body loss of volume and TYMP. Therefore, the decline in the heat loss responses, due to decrease in maximal oxygen consumption, may be masked by repeated endurance exercise training.