Seasonal variation in sweating responses of older and younger men.

Eight older (60-65 years) and six younger (20-25 years) men were exposed to a standard heat stress for 60 min in summer, autumn, winter, and spring. The test consisted of placing the lower legs and feet in a 42 degrees C water bath while sitting in constant environmental conditions (30 degrees C and 45% relative humidity). The increase of rectal temperature (delta Tre) was significantly greater (P < 0.05) in autumn, winter, and spring than in summer for the older group, but significantly greater only in winter than in summer for the younger group (P < 0.05). The delta Tre was greater for the older group in all seasons, but of significance only in autumn and spring (P < 0.01). There were no significant season-related differences for metabolic heat production (M) and mean skin temperature (Tsk) during the heat test in the respective groups, although the M and Tsk were lower for the older group in all seasons (P < 0.01). In the older group total body sweating rate (msw) divided by delta Tre (total msw/delta Tre) decreased from summer to winter (P < 0.02) and did not differ between winter and spring, whereas total msw/delta Tre in the younger group increased in spring after decreasing from autumn to winter (P < 0.03). The variations of the value, local sweating rate on the back and thigh divided by delta Tre (back msw/delta Tre and thigh msw/delta Tre), were similar to those of the total msw/delta Tre in each group, except for back msw/delta Tre in the younger group, which did not increase from winter to spring.(ABSTRACT TRUNCATED AT 250 WORDS)