Function of human eccrine sweat glands during dynamic exercise and passiveheat stress

The purpose of this study was to identify the pattern of change in the dens ity of activated sweat glands (ASG) and sweat output per gland (SGO) during dynamic constant-workload exercise and passive heat stress. Eight male sub jects (22.8 +/- 0.9 yr) exercised at a constant workload (117.5 +/- 4.8 W) and were also passively heated by lower-leg immersion into hot water of 42 degreesC under an ambient temperature of 25 degreesC and relative humidity of 50%. Esophageal temperature, mean skin temperature, sweating rate (SR), and heart rate were measured continuously during both trials. The number of ASG was determined every 4 min after the onset of sweating, whereas SGO wa s calculated by dividing SR by ASG. During both exercise and passive heatin g, SR increased abruptly during the first 8 min after onset of sweating, fo llowed by a slower increase. Similarly for both protocols, the number of AS G increased rapidly during the first 8 min after the onset of sweating and then ceased to increase further (P > 0.05). Conversely, SGO increased linea rly throughout both perturbations. Our results suggest that changes in fore arm sweating rate rely on both ASG and SGO during the initial period of exe rcise and passive heating, whereas further increases in SR are dependent on increases in SGO.