Exercise intensity effects on total sweat electrolyte losses and regional vs. whole-body sweat [Na+], [Cl-], and [K+]

Abstract

Purpose: To quantify total sweat electrolyte losses at two relative exercise intensities and determine the effect of workload on the relation between regional (REG) and whole body (WB) sweat electrolyte concentrations.

Methods: Eleven recreational athletes (7 men, 4 women; 71.5 ± 8.4 kg) completed two randomized trials cycling (30 °C, 44% rh) for 90 min at 45% (LOW) and 65% (MOD) of VO_2max in a plastic isolation chamber to determine WB sweat [Na⁺] and [Cl^-] using the washdown technique. REG sweat [Na⁺] and [Cl^-] were measured at 11 REG sites using absorbent patches. Total sweat electrolyte losses were the product of WB sweat loss (WBSL) and WB sweat electrolyte concentrations.

Results: WBSL (0.86 ± 0.15 vs. 1.27 ± 0.24 L), WB sweat [Na⁺] (32.6 ± 14.3 vs. 52.7 ± 14.6 mmol/L), WB sweat [Cl^-] (29.8 ± 13.6 vs. 52.5 ± 15.6 mmol/L), total sweat Na⁺ loss (659 ± 340 vs. 1565 ± 590 mg), and total sweat Cl^- loss (931 ± 494 vs. 2378 ± 853 mg) increased significantly (p < 0.05) from LOW to MOD. REG sweat [Na⁺] and [Cl^-] increased from LOW to MOD at all sites except thigh and calf. Intensity had a significant effect on the regression model predicting WB from REG at the ventral wrist, lower back, thigh, and calf for sweat [Na⁺] and [Cl^-].

Conclusion: Total sweat Na⁺ and Cl^- losses increased by ~ 150% with increased exercise intensity. Regression equations can be used to predict WB sweat [Na⁺] and [Cl^-] from some REG sites (e.g., dorsal forearm) irrespective of intensity (between 45 and 65% VO_2max), but other sites (especially ventral wrist, lower back, thigh, and calf) require separate prediction equations accounting for workload.

Keywords: Absorbent patch; Body map; Chloride; Potassium; Sodium.

Fig. 1

Body map showing the locations of regional patch placement

Fig. 2

Sweat sodium, chloride, and potassium concentrations and sweating rate during LOW and MOD intensity trials. n = 11 for all sites except D. Wrist and V. Wrist, where n = 10. D dorsal, V ventral. *p < 0.05, **p < 0.01, ***p < 0.001, LOW vs. MOD for whole body and 11-site aggregate (paired t tests). There was a significant main effect of intensity, region, and interaction on sweat [Na⁺] and [Cl⁻]. For sweat [K⁺] and RSR, there was a significant main effect of intensity and region, but no interaction. ^#p < 0.05, LOW vs. MOD within sites (after Tukey’s post hoc adjustment for multiple comparisons). Letters indicate regional differences collapsed across intensities (sites sharing same letter are not significantly different)

Fig. 3

Total sweat sodium, chloride, and potassium losses during LOW and MOD intensity trials. *p < 0.05, LOW vs. MOD

Fig. 4

Ratio between regional and whole-body measures of sweat sodium, chloride, and potassium concentrations as well as sweating rate during LOW and MOD intensity trials. n = 11 for all sites except D. Wrist and V. Wrist, where n = 10. D dorsal, V ventral. *p < 0.05, LOW vs. MOD for 11-site aggregate (paired t tests). There was a significant main effect of intensity and region, but no interaction on the sweat [Na⁺], [Cl⁻], and [K⁺] ratios. There was a significant main effect of region, but no effect of intensity or interaction on the sweating rate ratio. Letters indicate regional differences collapsed across LOW and MOD (sites sharing same letter are not significantly different). Dashed line indicates ratio of 1.0 (regional = whole body)