The effects of passive heating and head-cooling on perception of exercise in the heat

The capacity to perform exercise is reduced in a hot environment when compared to cooler conditions. A limiting factor appears to be a higher core body temperature (T _core) and it has been suggested that an elevated T _core reduces the drive to exercise, this being reflected in higher ratings of perceived exertion (RPE). The purpose of the present study was to determine whether passive heating to increase T _core would have a detrimental effect on RPE and thermal comfort during subsequent exercise in the heat and whether head-cooling during passive heating would attenuate these unpleasant sensations of an elevated T _core during subsequent exercise in the heat. Nine physically-active, non-heat-acclimated volunteers [6 males, 3 females; age: 21 ± 1 year, \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{{\text{2max}}}} : \) 50 ± 9 ml kg⁻¹·min⁻¹, peak power output: 286 ± 43 W (mean ± SD)] performed two 12-minute constant-load cycling tests at 70% \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{{\text{2max}}}} \) in a warm-dry environment (34 ± 1°C, relative humidity <30%) separated by a period of passive heating in a sauna (68 ± 3°C) to increase T _core. In one trial, subjects had their head and face cooled continually in the sauna (HC), the other trial was a control (CON). Passive heating increased T _core by 1.22 ± 0.03°C in the CON and by 0.75 ± 0.07°C in the HC trial (P < 0.01). Passive heating increased weighted mean skin temperature (T _msk) in both the CON and HC trials (P < 0.01), however, head-cooling lowered T _msk during passive heating (P < 0.05). Exercise time following passive heating was reduced in both the CON and HC trials (P < 0.05). Passive heating increased RPE (P < 0.01), however, RPE was lower following passive heating with head-cooling (P < 0.05). There was a significant correlation between T _core and RPE (r = 0.82, P < 0.001). In conclusion, our results suggest increased RPE during exercise in the heat is primarily due to the increase in T _core. Furthermore, head-cooling attenuates the rise in T _core and the effect on RPE is proportional to the rise on T _core.