The independent roles of temperature and thermal perception in the control of human thermoregulatory behavior.

The present study independently evaluated temperature and thermal perception as controllers of thermoregulatory behavior in humans. This was accomplished using a self-paced exercise and heat stress model in which twelve physically active male subjects exercised at a constant subjective rating of perceived exertion (16, 'hard--very hard') while their face was thermally and non-thermally cooled, heated, or left alone (control trial). Thermal cooling and heating were achieved via forced convection, while non-thermal cooling and heating were accomplished via the topical application of menthol and capsaicin solutions. Evidence for thermoregulatory behavior was defined in terms of self-selected exercise intensity, and thus exercise work output. The results indicate that, in the absence of changes in temperature, non-thermal cooling and warming elicited thermal sensory and discomfort sensations similar to those observed during thermal cooling and warming. Furthermore, the perception of effort was maintained throughout exercise in all trials, while the initial and final exercise intensities were also similar. Thermal and non-thermal cooling resulted in the highest work output, while thermal warming the lowest. Non-thermal warming and control trials were similar. Heart rate, mean skin and core (rectal) temperatures, and whole body and local (neck) sweat rates were similar between all trials. These data indicate that changes in temperature are not a requirement for the initiation of thermoregulatory behavior in humans. Rather, thermal sensation and thermal discomfort are capable behavioral controllers.