The present study investigated whether face cooling reduced both the perceived exertion (RPE) and prolactin (PRL) release during hyperthermic exercise. Ten, non-heat-acclimated males (23 ± 2 years; maximal oxygen consumption, 56 ± 7 ml kg -1 min -1 [mean ± S.D.]) exercised for 40 min on a cycle ergometer at 65% of their peak aerobic power, at an ambient temperature of 33• C (27% relative humidity) with (FC) and without face cooling as a control (CON). With FC, forehead temperature was maintained ∼6• C lower than CON, while other skin sites were similar or slightly warmer in the FC condition. Rectal temperature increased by ∼1.5• C with the same time course in both conditions. A relative bradycardia was observed during FC, with heart rate approximately 5 beats min -1 lower than CON (P < 0.05). Mean plasma lactate was lower during FC (FC, 5.0 ± 0.3 mmol l -1 ; CON, 5.9 ± 0.3 mmol l -1 ; P < 0.05) but no differences were observed for plasma glucose, which remained constant during exercise. Levels of PRL were maintained at 175 ± 17 mIU l -1 during exercise for FC, while values for CON increased to a peak of 373 ± 22 mIU l -1 so that towards the end of the exercise, for the same rectal temperature, PRL was significantly lower in the FC condition (P < 0.05). Global and breathing RPE were reduced but only towards the end of the 40 min of exercise during FC, whilst subjective thermal comfort was significantly lower during FC (P < 0.05). We confirm the substantial effect that FC has on the secretion of PRL during hyperthermic exercise but show that it makes a relatively small contribution to the perception of effort when compared to the effect of a cool total skin area as occurs with exercise in a thermoneutral environment.

The purpose of the present study was twofold: first, to determine the extent to which elevated skin temperature is responsible for the hormonal and perceptual responses to passive heating; and second, to determine to what extent face-cooling can override the effects of raised skin temperature. Sixteen recreationally active, non-heat-acclimated volunteers (12 male, 4 female; age, 29 ± 9 years, [mean ± S.D.]) underwent a passive heat exposure for 60 min in a sauna maintained at 58 • C (13% relative humidity), conditions under which sweating effectively maintains core temperature. Subjects were allocated to one of two experimental groups which were matched for sex, age, body mass index, body surface area and sweating response; one group received face cooling (FC) every 5 min, whilst the other control group (CON) received none. Mean skin temperatures were elevated by ∼4 • C for the 60 min duration (CON, 36.5 ± 0.1 • C; FC, 35.7 ± 0.1 • C; P < 0.05) but core temperature rose by only ∼0.25 • C with no difference between groups. Circulating prolactin remained stable and showed no increase for the FC group, whereas concentrations increased by 102 ± 34% (P < 0.05) for the CON group. No differences were observed between groups for heart rate, but the sensation of heat was less (P < 0.05) with FC. We suggest that a significant component of the prolactin response to moderate passive heating is mediated by facial skin temperature, and selective cooling of the face is associated with improved perception of thermal comfort. These results indicate that the temperature of only a small part of the total skin area (∼10%) has a disproportionately large effect on the hormonal and perceptual responses to heat stress.