Local cooling during hot water immersion improves perceptions without inhibiting the acute interleukin-6 response

PURPOSE Passive elevation of body temperature can induce an acute inflammatory response that has been proposed to be beneficial; however, it can be perceived as uncomfortable. Here, we investigate whether local cooling of the upper body during hot water immersion can improve perception without inhibiting the interleukin-6 (IL-6) response. METHODS Nine healthy male participants (age: 22 ± 1 years, body mass: 83.4 ± 9.4 kg) were immersed up to the waist for three 60-min water immersion conditions: 42 °C hot water immersion (HWI), 42 °C HWI with simultaneous upper-body cooling using a fan (FAN), and 36 °C thermoneutral water immersion (CON). Blood samples to determine IL-6 plasma concentration were collected pre- and post-water immersion; basic affect and thermal comfort were assessed throughout the intervention. RESULTS Plasma IL-6 concentration was higher for HWI and FAN when compared with CON (P < 0.01) and did not differ between HWI and FAN (P = 0.22; pre to post, HWI: 1.0 ± 0.6 to 1.5 ± 0.7 pg·ml-1, FAN: 0.7 ± 0.5 to 1.1 ± 0.5 pg·ml-1, CON: 0.5 ± 0.2 to 0.5 ± 0.2 pg·ml-1). At the end of immersion, basic affect was lowest for HWI (HWI: - 1.8 ± 2.0, FAN: 0.2 ± 1.6, CON 1.0 ± 2.1, P < 0.02); thermal comfort for HWI was in the uncomfortable range (3.0 ± 1.0, P < 0.01 when compared with FAN and CON), whereas FAN (0.7 ± 0.7) and CON (-0.2 ± 0.7) were in the comfortable range. CONCLUSION Local cooling of the upper body during hot water immersion improves basic affect and thermal comfort without inhibiting the acute IL-6 response.