Intense exercise increases the post-exercise threshold for sweating

Abstract

We demonstrated previously that esophageal temperature (T _es) remains elevated by ≈0.5°C for at least 65 min after intense exercise. Following exercise, average skin temperature (T _avg) and skin blood flow returned rapidly to pre-exercise values even though T _es remained elevated, indicating that the T _es threshold for vasodilation is elevated during this period. The present study evaluates the hypothesis that the threshold for sweating is also increased following intense exercise. Four males and three females were immersed in water (water temperature, T _w = 42°C) until onset of sweating (Immersion 1), followed by recovery in air (air temperature, T _a = 24°C). At a T _a of 24°C, 15 min of cycle ergometry (70% VO_2max) (Exercise) was then followed by 30 min of recovery. Subjects were then immersed again (T _w = 42°C) until onset of sweating (Immersion 2). Baseline T _es and T _skavg were 37.0 (0.1)°C and 32.3 (0.3)°C, respectively. Because the T _skavg at the onset of sweating was different during Exercise [30.9 (0.3)°C] than during Immersion 1 and Immersion 2 [36.8 (0.2)°C and 36.4 (0.2)°C, respectively] a corrected core temperature, T _es (calculated), was calculated at a single designated skin temperature, T _{sk(designated)}, as follows: T _{es(calculated)} = T _es + [β/(1−β)][T _skavg−T _{sk(designated)}]. The T _{sk(designated)} was set at 36.5°C (mean of Immersion 1 and Immersion 2 conditions) and β represents the fractional contribution of T _skavg to the sweating response (β for sweating = 0.1). While T _{es(calculated)} at the onset of sweating was significantly lower during exercise [36.7 (0.2)°C] than during Immersion 1 [37.1 (0.1)°C], the threshold of sweating during Immersion 2 [37.3 (0.1)°C] was greater than during both Exercise and Immersion 1 (P < 0.05). We conclude that intense exercise decreases the sweating threshold during exercise itself, but elicits a subsequent short-term increase in the resting sweating threshold.