Skin blood flow and sweating changes following exercise training and heat acclimation.

Eight subjects underwent an exercise training program (10 days at 75% VO2max for 1 h/day at 25 degrees C db/13 degrees C wb) and a heat-acclimation program (10 days at 50% VO2max for 1 h/day at 35 degrees C db/32 degrees C wb). The relations of chest sweat rate and of forearm blood flow to internal temperature were determined for each subject at a 25 degrees C ambient temperature before training, between training and acclimation, and following acclimation. Training shifted the vasodilation and sweating thresholds toward lower internal temperatures, and acclimation further lowered these thresholds. All threshold shifts were statistically significant (P less than 0.05). Training and acclimation both appeared to increase the slope of the sweating relation, but these effects were not statistically significant. Changes in the slope of the blood flow relation were small and inconsistent. Since arm blood flow is higher at any given internal temperature after acclimation, the lower blood flow which is reported to accompany heat acclimation must result from the lower body temperatures.