Disappearance of seasonal variation of sweating responses in exercising man: effect of pre-heating in cold season.

The present study was designed to investigate the seasonal variation in thermal responses during moderate exercise. In winter, exercise was done after pre-heating for 30 min at an ambient temperature of 30 degrees C. Adult healthy men repeated the exercise at 40% of maximal oxygen uptake by a bicycle ergometer in a climatic chamber of an ambient temperature of 30 degrees C (relative humidity, 45%) in winter, spring, summer, and fall. In summer, the sweat rate increased immediately after the exercise started, whereas in winter it took in several minutes. The average sweat rate during exercise was significantly different (p < 0.01) in winter and compared to the other seasons. Significantly (p < 0.01) negative correlations were found between sweat rate and the rate of change of the mean skin temperature in each season. The regression equation was significantly (p < 0.01) different between winter and summer. After the pre-heating in winter, the sweating responses during exercise were similar to the responses in the summer. Thus, by thermal stimuli, the heat dissipation, especially skin evaporation due to sweating, may be stimulated in the cold season. It is suggested that sweating may be facilitated by not only the heat dissipation capacity of the hypothalamic mechanism with the thermal information via skin thermoreceptors but also by a change of peripheral sweat gland activity. Furthermore, the fall in skin temperature during the initial exercise may not be due to increased evaporative cooling, but to the vasoconstriction probably caused by non-thermal factors.