Increase in sweating sensitivity by endurance conditioning in man

Sweating sensitivity has been evaluated at rest in 10 competitive athletes (cross-country skiers and swimmers). Three sedentary men underwent a 3-mo period of endurance training in a temperate climate, (dry bulb temperature (Tdb): 18 degrees C) and had their sweating sensitivity measured before and after the training period. Mean maximum oxygen uptake (Vo2max, ml.min(-1).kg(-1)) was: skiers: 66.5; swimmers 65.8; sedentary men, pretraining 40.9; posttraining: 48.3 (+18%). Sweat output of athletes under a given stress (passive heating) was markedly higher than that of sedentary men. Skiers exhibited a high level of heat tolerance and were better acclimatized than swimmers, although they had never experienced exposure to heat. The increase in Vo2max of sedentary men was accompanied by 1) an increase in sweating sensitivity with a decrease of body heat storage at steady state (pretraining: 5.4 kJ.kg(-1); posttraining: 3.5 kJ.kg(-1); P less than 0.05); 2) significant shift down the temperature scale with reduced rectal temperature (Tre) for sweat onset; 3) an increase of gain constants of sweating (W.m-2 degrees C(-1) (pretraining: 168; posttraining: 269; gain constant of swimmers: 222). It was suggested that endurance training in cold or temperate conditions with significant increase of Vo2max could act on the thermoregulatory function in a way similar to body heating procedures, such as work in heat, and could contribute to heat acclimatization.