Long - term aerobic training augments peripheral sudomotor sensitivity to acetylcholine ( Physical training modifies peripheral sudomotor mechanisms )

Higher sweating in trained, compared to sedentary men has been attributed to differences in the peripheral sweating mechanisms, although such mechanisms have not been completely investigated in comparative terms. The aim of this study is to quantitatively investigate the peripheral sudomotor adaptive mechanisms attributed for greater sweating in endurance-trained athletes as opposed to sedentary men. To do this, we compared sudomotor activities to acetylcholine(ACh) iontophoresed in the fore arm skins of trained versus untrained subjects. Changes in fore arm skin blood flow(SBF), skin and body temperatures, sweating rate(SW), sweat onset time(SOT), active sweat gland density (SGD), and single sweat gland output(SGO) were measured. Training-related differences were observed for SBF, SW, SOT, SGD, SGO and skin temperature. Peripheral SW [axon-reflex(AXR), 2.88±0.94 vs 2.02±0.88, and direct (DIR) 6.77±1.29 vs 5.19±0.0.86; for the trained and untrained respectively] were 43% and 30% higher in the endurance-trained compared to the untrained men. SOT was 0.41 min earlier, SGD was 15%, SGO 50 and SBF 2 fold higher in the endurance-trained men. Maximum VO2 was higher in the endurance-trained compared to the sedentary. Furthermore, when VO2 was regressed against sweat output, the endurance-trained had higher correlation (r2=0.89, P＜0.0001) than that of the sedentary (r2=0.33, P＜0.05), suggesting that proportionally less amount of sweat was used for heat dissipation in the trained. It was concluded that endurance-trained athletes had higher sweat outputs due to the combinations of a higher sweat output per activated sweat gland, shorter lag phase for sweating, higher number of activated sweat glands and higher skin blood flow than those of non-trained sweats.