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