Independent Influence of Skin Temperature on Whole-Body Sweat Rate.

Hospers, Lily; Cheuvront, Samuel N; Kenefick, Robert W; Jay, Ollie

PURPOSE It is often assumed a person with a higher mean skin temperature (Tsk) will sweat more during exercise. However, it has not yet been demonstrated whether Tsk describes any individual variability in whole-body sweat rate (WBSR) independently of the evaporative requirement for heat balance (Ereq). METHODS 140 bouts of 2-h treadmill walking completed by a pool of 21 participants (23±4 y, 174±8 cm, 76±11 kg, 1.9±0.2 m) under up to 9 conditions were analyzed. Trials employed varying rates of metabolic heat production (Hprod) (197-813 W), and environmental conditions (15°C, 20°C, 25°C, 30°C; all 50% RH), yielding a wide range of Ereq (86-684 W) and Tsk values (26.9-34.4°C). RESULTS The individual variation observed in WBSR was best described using Ereq (in W) (R=0.784) as a sole descriptor, relative to Ereq (in W·m) (R=0.735), Hprod (in W) (R=0.639), Hprod (in W·m) (R=0.584), Ta (R=0.263) and Tsk (R=0.077); all P<0.001. A multiple stepwise linear regression included only Ereq (in W) (adjusted R=0.784), with Tsk not significantly correlating with the residual variance (P=0.285), independently of Ereq (in W). Hprod (in W) had similar predictive strength to Ereq (in W) at a fixed air temperature, explaining only 5.2% at 30°C, 4.9% at 25°C, 2.7% at 20°C and 0.5% at 15°C (all P<0.001) less variance in WBSR compared to Ereq. However, when data from all ambient temperatures were pooled, Hprod alone was a markedly worse predictor of WBSR than Ereq (R=0.639 vs. 0.784; P<0.001). CONCLUSION Ereq (in W) explained approximately four-fifths of the individual variation in WBSR over a range of ambient temperatures and exercise intensities, while Tsk did not explain any residual variance independently of Ereq.