Mechanisms of potentiation in sweating induced by long-term physical training

Abstract

To evaluate the mechanism of potentiation of sweating after long-term physical training, we compared sweating function in trained and untrained subjects using the frequency of sweat expulsion (f _sw) as an indicator of central sudomotor activity. Nine trained male subjects (trained group) and eight untrained male subjects (untrained group) performed 30-min cycle exercise at 35% maximal oxygen uptake at 25°C ambient temperature and 35% relative humidity. Oesophageal temperature (T _oes), mean body temperature$\overline T$ _b, chest sweating rate ($\dot m$ _sw,chest), forearm sweating rate ($\dot m$ _forearm), andf _sw were measured. The slopes of the$\dot m$ _sw,chest versus body temperature (T _oes and$\overline T$ _b) and versusf _sw relationships in the trained group were significantly greater than those in the untrained group (both,P < 0.05), while there was no difference between the groups in the slopes of the$\dot m$ _sw,chest versus body temperature or versusf _sw relationships. Neither the body temperature threshold for initiation of chest or forearm sweating nor the slope of thef _sw-$\overline T$ _b relationship differed between groups. We concluded that, during light exercise at moderate ambient temperature, the$\dot m$ _sw,chest in the subjects who had undergone long-term physical training was greater than that in the untrained subjects while the$\dot m$ _sw,forearm was not changed. The greater$\dot m$ _sw,chest in the trained subjects was concluded to be due to an increase of sensitivity of peripheral mechanisms.