Influence of topical capsaicin cream on thermoregulation and perception during acute exercise in the heat

Purpose: Determine if topical capsaicin, a transient receptor potential vanilloid heat thermoreceptor activator, alters thermoregulation and perception when applied topically prior to thermal exercise. Methods: Twelve subjects completed 2 treatments. Subjects walked (1.6 m s-1, 5% grade) for 30 min in the heat (38 degrees C, 60% relative humidity) with either a capsaicin (0.025% capsaicin) or control cream applied to the upper (shoulder to wrist) and lower (mid-thigh to ankle) limbs covering similar to 50% body surface area. Skin blood flow (SkBF), sweat (rate, composition), heart rate, temperature (skin, core), and perceived thermal sensation were measured prior to and during exercise. Results: The relative change in SkBF was not different between treatments at any time point (p = 0.284). There were no differences in sweat rate between the capsaicin (1.23 +/- 0.37 L h(-1)) and control (1.43 +/- 0.43 L h(-1), p = 0.122). There were no differences in heart rate between the capsaicin (122 +/- 38 beats.min(-1)) and control (125 +/- 39 beats.min(-1), p = 0.431). There were also no differences in weighted surface (p = 0.976) or body tem-peratures (p = 0.855) between the capsaicin (36.0 +/- 1.7 degrees C, 37.0 +/- 0.8 degrees C, respectively) and control (36.0 +/- 1.6 degrees C, 36.9 +/- 0.8 degrees C, respectively). The capsaicin treatment was not perceived as hotter than the control treatment until minute 30 of exercise (2.8 +/- 0.4, 2.5 +/- 0.5, respectively, p = 0.038) Conclusions: Topical capsaicin application does not alter whole-body thermoregulation during acute exercise in the heat despite perceiving the treatment as hotter late in exercise.