Effect of exercise intensity on the postexercise sweating threshold

Abstract

The hypothesis that the magnitude of the postexercise onset threshold for sweating is increased by the intensity of exercise was tested in eight subjects. Esophageal temperature was monitored as an index of core temperature while sweat rate was measured by using a ventilated capsule placed on the upper back. Subjects remained seated resting for 15 min (no exercise) or performed 15 min of treadmill running at either 55, 70, or 85% of peak oxygen consumption (V̇o2 peak) followed by a 20-min seated recovery. Subjects then donned a liquid-conditioned suit used to regulate mean skin temperature. The suit was first perfused with 20°C water to control and stabilize skin and core temperature before whole body heating. Subsequently, the skin was heated (∼4.0°C/h) until sweating occurred. Exercise resulted in an increase in the onset threshold for sweating of 0.11 ± 0.02, 0.23 ± 0.01, and 0.33 ± 0.02°C above that measured for the no-exercise resting values ( P < 0.05) for the 55, 70, and 85% of V̇o2 peak exercise conditions, respectively. We did note that there was a greater postexercise hypotension as a function of exercise intensity as measured at the end of the 20-min exercise recovery. Thus it is plausible that the increase in postexercise threshold may be related to postexercise hypotension. It is concluded that the sweating response during upright recovery is significantly modified by exercise intensity and may likely be influenced by the nonthermal baroreceptor reflex adjustments postexercise.