MECHANISMS OF POTENTIATION IN SWEATING INDUCED BY LONG-TERM PHYSICAL-TRAINING

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 degrees C ambient temperature and 35% relative humidity. Oesophageal temperature (T-oes), mean body temperature (($) over bar T-b), chest sweating rate (m(sw,chest)), forearm sweating rate (m(sw,forearm)), and f(sw) were measured. The slopes of the m(sw,chest) versus body temperature (T-oes and ($) over bar T-b) and versus f(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 m(sw,forearm) versus body temperature or versus f(sw) relationships. Neither the body temperature threshold for initiation of chest or forearm sweating nor the slope of the f(sw)-($) over bar T-b relationship differed between groups. We concluded that, during light exercise at moderate ambient temperature, the m(sw,chest) in the subjects who had undergone longterm physical training was greater than that in the untrained subjects while the m(sw,forearm) was not changed. The greater m(sw,chest) in the trained subjects was concluded to be due to an increase of sensitivity of peripheral mechanisms.