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± .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), 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.