Is sweat rate during steady state exercise related to maximum oxygen uptake?

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Abstract

The purpose of this study was to investigate whether whole-body sweat rate induced by exercise (SRex) at the same oxygen uptake could be correlated with individual maximum oxygen uptake (peak oxygen uptake (V˙O2peak)). A secondary purpose was to examine the relationship between SRex and local sweat rate induced by pilocarpine on the forearm at rest (SRpilo). Nine healthy young males (V˙O2peak 55.2 (12.3) mL min−1 kg−1, mean (SD); 43.3–76.1 mL min−1 kg−1, range), acclimatized to a tropical climate had their sweating stimulated in two situations: (1) exercise-induced whole-body sweat by 120 min of cycling exercise at a constant submaximal oxygen uptake of 1.65 L min−1 or (2) pilocarpine-induced sweat on the right forearm with 0.5% pilocarpine hydrochloride (1.5 mA, 5 min) at rest. The SRex was not correlated with V˙O2peak (r=-0.53, p=0.14). In addition, there was not correlation between SRex (0.38 (0.03) mg cm−2 min−1) and SRpilo (0.36 (0.20) mg cm−2 min−1) (r=0.23, p=0.57). These results suggest that whole-body sweat rate during exercise at the same oxygen uptake in a temperate environment is not related to V˙O2peak. Furthermore, the eccrine sweat gland does not respond similarly for local pilocarpine or exercise stimuli.

Introduction

The evaporation of sweat secreted by eccrine sweat glands during exercise is an important way to dissipate heat and to control body temperature. The ability to produce sweat is affected by heat acclimation (Robison et al., 1943; Nadel et al., 1974; Patterson et al., 2004), hydration status (Candas et al., 1988), age (Anderson and Kenney, 1987), gender (Buono and Sjoholm, 1988), and physical training (Nadel et al., 1974; Sato and Sato, 1983; Buono and Sjoholm, 1988; Buono et al., 1991). Heat acclimation and physical training probably promote local adaptations on eccrine sweat glands, such as increased size, capacity and cholinergic sensitivity (Sato and Sato, 1983; Sato et al., 1990).

Previous researches demonstrated that local adaptations of eccrine sweat gland could be observed using in vivo or in vitro stimulation through pharmacological induction (pilocarpine or methacholine) (Sato and Sato, 1983; Buono and Sjoholm, 1988; Sato et al., 1990; Buono et al., 1991; Kondo et al., 1999). Buono and Sjoholm (1988) reported that trained men and women had greater local sweat rates after pilocarpine stimulation compared to sedentary men and women at rest. Sato and Sato (1983) also showed that eccrine sweat glands of individuals assumed as poor sweaters exhibited smaller size, lower activity and decreased cholinergic sensitivity than the glands of physically fit individuals.

Buono et al. (1991) observed a significant correlation between whole-body sweat rate induced by steady state exercise (SRex) and maximum oxygen uptake (V˙O2max) in trained and untrained subjects. They also verified a significant correlation between SRex and sweat rate induced on the forearm by pilocarpine at rest (SRpilo). The authors suggested that endurance training probably resulted in increases in the sweating capacity of the sweat gland itself, and that SRpilo could serve as an index of whole-body sweat rate during non-resting thermoregulatory stress, such as steady state exercise. However, that study measured SRex using 70% of the V˙O2max in two groups with different V˙O2max (trained and untrained), which resulted in different oxygen uptake and heat production.

Therefore, the main purpose of the present study was to determine whether whole-body sweat rate produced by exercise at the same oxygen uptake correlate with maximum oxygen uptake (peak oxygen uptake (V˙O2peak)). A secondary purpose was to evaluate the relationship between whole-body sweat rate induced by exercise and local sweat rate induced by iontophoresis with pilocarpine at rest. Our hypotheses were that whole-body sweat rate during exercise should not be correlated with V˙O2peak, and local sweat rate induced by pilocarpine should not be correlated with whole-body sweat rate during exercise.

Section snippets

Methods

This study was approved by the Research and Ethics Committee of the Federal University of Minas Gerais (no. 023/2003). All procedures were performed according to the resolution 196 of the National Health Council (1996) on scientific research involving humans. Prior to participation, each subject was informed regarding the procedures, and written consent was obtained.

Results

All subjects completed 120 min of exercise at 112 (9) W, which required 1.64 (0.12) L O2 min−1, as previously planned. There was not significant correlation between SRex and V˙O2peak (p=0.14) (Fig. 1). Fig. 2, Fig. 3 show a non significant correlation between SRpilo and V˙O2peak, and SRpilo and SRex (p=0.25 and 0.55, respectively).

The mean value SRex (0.38 (0.03) mg cm−2 min−1) was not different from the mean value of SRpilo (0.36 (0.20) mg cm−2 min−1) (p=0.85) (Fig. 4). However, SRex ranged from 0.33 to

Discussion

The present study did not observe a significant correlation between SRex during steady state exercise and V˙O2peak (Fig. 1), as hypothesized. Moreover, our data showed a narrow range of SRex although the volunteers exhibited a wide range V˙O2peak. These results suggest that the improved ability to produce sweat induced by physical training on eccrine sweat glands is not necessarily expressed during a prolonged exercise with constant oxygen uptake in a temperate environment.

Traditionally sweat

Acknowledgements

The authors gratefully acknowledge Professor Suzanne Schneider and Paulette Yamada (University of New Mexico, USA) and Professor Nigel Anthony Southworth Taylor (University of Wollongong, Australia) for their useful suggestions about the paper and also the colleagues Samuel Penna Wanner, Juliana Bohnen Guimarães from the Laboratório de Fisiologia do Exercício (Universidade Federal de Minas Gerais). The study was supported by CAPES and CNPq.

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