CONTROL OF THERMOREGULATORY SWEATING IS ALTERED BY HYDRATION LEVEL AND EXERCISE INTENSITY

The purpose of this study was to examine the thermoregulatory sweating control parameters of threshold temperature and sensitivity to determ ine whether 1) these variables were altered by hypohydration level and exercise intensity and 2) these alterations, if present, were additiv e and independent. Nine heat-acclimated men completed a matrix of nine trials: three exercise intensities of 25, 45, and 65% maximal O-2 upt ake and three hydration levels, i.e., euhydration and hypohydration (H y) at 3 and 5% of body weight. During each trial, subjects attempted 5 0 min of treadmill exercise in a warm room (30 degrees C dry bulb, 50% relative humidity) while esophageal temperature and upper arm sweatin g rate were continuously measured. Hypohydration was achieved by exerc ise and fluid restriction the day preceding the trials. The following new findings were made: 1) threshold temperature increased in graded m anner with hypohydration level (similar to 0.06 degrees C/%Hy); 2) sen sitivity decreased in a graded manner with hypohydration level (simila r to 0.06 units/%Hy); 3) threshold temperature was not altered by exer cise intensity; and 4) sensitivity increased from low- to moderate- an d high-intensity exercise. We conclude that both hypohydration level a nd exercise intensity produce independent effects on control of thermo regulatory sweating.