Abstract
PurposeTo 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.MethodsEleven 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 VO2max 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.ResultsWBSL (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−].ConclusionTotal 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% VO2max), but other sites (especially ventral wrist, lower back, thigh, and calf) require separate prediction equations accounting for workload.
Highlights
Communicated by George Havenith.Thermoregulatory sweat is comprised of several electrolytes, including sodium (Na+), chloride (Cl−), and potassium (K+)
REG and whole body (WB) sweat electrolyte concentrations were measured during LOW and MOD relative exercise intensities to determine the effect of increasing workload on WB sweat electrolyte concentrations, total sweat electrolyte losses, and the relation between REG and WB sweat electrolyte concentrations
Regression equations may be useful in predicting WB sweat [ Na+] and [ Cl−] from some REG sites irrespective of intensity when exercising between 45 and 65% VO2max, but other sites require separate prediction equations that account for workload
Summary
Communicated by George Havenith.Thermoregulatory sweat is comprised of several electrolytes, including sodium (Na+), chloride (Cl−), and potassium (K+). It is well established that sweat electrolyte, Na+ and Cl−, losses during exercise vary considerably within and between athletes (Baker et al 2016; Sawka et al 2007). One reason for this variability is exercise intensity differences across training sessions/competition. Few have studied the effect of exercise intensity on WB sweat [Na+], [Cl−], and [ K+] and total WB sweat electrolyte losses. Lemon et al (1986) made WB sweat measurements in six men during treadmill exercise and found that sweat urea nitrogen loss increased with changes in intensity from 42 to 67% maximal oxygen uptake (VO2max); electrolytes were not measured in the WB sweat. Having a better understanding of how WB sweat electrolyte concentrations as well as WBSR are modified by workload can help to inform athletes’ fluid/ electrolyte replacement strategies for different intensities of training/competition
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