Reflex regulation of sweat rate by skin temperature in exercising humans.

To find whether sweat rate (SR) and forearm skin blood flow ( SkBF ) were reflexly affected by skin temperature (Tsk) we used water-perfused suits to rapidly elevate Tsk during exercise. With this elevation in Tsk, there was a period of little net change in esophageal temperature (Tes) but marked responses in SR and SkBF . During this period a rise in Tsk of 4.2 +/- 0.3 degrees C was associated with an increase in SR of 0.44 +/- 0.09 mg X cm-2 X min-1 and an increase in SkBF of 3.27 +/- 0.42 ml X 100 ml-1 X min-1. Multiple linear regression analysis as well as comparison with control studies in which Tsk was kept cool also reveal a consistent role for Tsk in the reflex regulation of SR and SkBF . Responses in SR and FBF were much more marked at levels of Tsk below 33 degrees C. Below a Tsk of 33 degrees C, SR rose 0.30 +/- 0.06 mg X cm-2 X min-1 per degrees C rise in Tsk, whereas above 33 degrees SR rose only 0.05 +/- 0.01 mg X cm2 X min per degrees C. FBF rose 2.81 +/- 0.60 and 0.77 +/- 0.18 ml X 100 ml-1 X min-1 per degrees C rise in Tsk at the lower and upper ranges of Tsk, respectively.