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 Tcore 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 Tcore 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 Tcore during subsequent exercise in the heat. Nine physically-active, non-heat-acclimated volunteers [ 6 males, 3 females; age: 21 +/- 1 year, VO(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% VO(2max) in a warm-dry environment (34 +/- 1 degrees C, relative humidity < 30%) separated by a period of passive heating in a sauna (68 +/- 3 degrees 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 degrees C in the CON and by 0.75 +/- 0.07 degrees 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 Tmsk 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).