Abstract
Centrally stimulated sweat rate produced by graded exercise until exhaustion was compared to the local sweat rate induced by pilocarpine, often used as a sweating index for healthy individuals. Nine young male volunteers (22 +/- 4 years) were studied in temperate environment in two situations: at rest and during progressive exercise with 25 W increases every 2 min until exhaustion, on a cycle ergometer. In both situations, sweating was induced on the right forearm with 5 ml 0.5% pilocarpine hydrochloride applied by iontophoresis (1.5 mA, 5 min), with left forearm used as control. Local sweat rate was measured for 15 min at rest. During exercise, whole-body sweat rate was calculated from the body weight variation. Local sweat rate was measured from the time when heart rate reached 150 bpm until exhaustion and was collected using absorbent filter paper. Pharmacologically induced local sweat rate at rest (0.4 +/- 0.2 mg cm-2 min-1) and mean exercise-induced whole-body sweat rate (0.4 +/- 0.1 mg cm-2 min-1) were the same (P > 0.05) but were about five times smaller than local exercise-induced sweat rate (control = 2.1 +/- 1.4; pilocarpine = 2.7 +/- 1.2 mg cm-2 min-1), indicating different sudorific mechanisms. Both exercise-induced whole-body sweat rate (P < 0.05) and local sweat rate (P < 0.05) on control forearm correlated positively with pilocarpine-induced local sweat rate at rest. Assuming that exercise-induced sweating was a result of integrated physiological mechanisms, we suggest that local and whole-body sweat rate measured during graded exercise could be a better sweating index than pilocarpine.
Highlights
The ability of humans to dissipate heat during exercise and in hot environments depends mainly on the evaporation of sweat secreted by the eccrine sweat glands
There was a positive and significant correlation between the pilocarpine-induced local sweat rate at rest and whole-body and local sweat rate during graded exercise tests until exhaustion (GXT) (Figure 3), indicating that both variables could be used as an index of sweat gland output
GXT is a more widely used procedure for the measurement of aerobic power, for clinical diagnosis and for exercise prescription than pilocarpine iontophoresis, a method practically restricted to the diagnosis of cystic fibrosis and to scientific studies
Summary
The ability of humans to dissipate heat during exercise and in hot environments depends mainly on the evaporation of sweat secreted by the eccrine sweat glands. Sweat production is essential for heat tolerance, which prevents hyperthermia and influences performance during physical activity [1]. The local sweat rate has been measured during pharmacological stimulation of the eccrine sweat glands with cholinergic agonists (methacholine, acetylcholine, pilocarpine) injected subcutaneously or administered by iontophoresis. The sweat rate induced by cholinergic agents is considered to reflect the maximal rate [2], and the sweat rate induced by pilocarpine at rest is regarded to be an objective index of sweat gland output and to reflect sweat production during continuous exercise [3,4,5,6]
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