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. 2020 Aug;8(15):e14524.
doi: 10.14814/phy2.14524.

Cross-validation of equations to predict whole-body sweat sodium concentration from regional measures during exercise

Lindsay B Baker  1 , Ryan P Nuccio  1 , Adam J Reimel  1 , Shyretha D Brown  1 , Corey T Ungaro  1 , Peter John D De Chavez  2 , Kelly A Barnes  1
Affiliations

Cross-validation of equations to predict whole-body sweat sodium concentration from regional measures during exercise

Lindsay B Baker et al. Physiol Rep. 2020 Aug.

Abstract

We have previously published equations to estimate whole-body (WB) sweat sodium concentration ([Na+ ]) from regional (REG) measures; however, a cross-validation is needed to corroborate the applicability of these prediction equations between studies. The purpose of this study was to determine the validity of published equations in predicting WB sweat [Na+ ] from REG measures when applied to a new data set. Forty-nine participants (34 men, 15 women; 75 ± 12 kg) cycled for 90 min while WB sweat [Na+ ] was measured using the washdown technique. REG sweat [Na+ ] was measured from seven regions using absorbent patches (3M Tegaderm + Pad). Published equations were applied to REG sweat [Na+ ] to determine predicted WB sweat [Na+ ]. Bland-Altman analysis of mean bias (raw and predicted minus measured) and 95% limits of agreement (LOA) were used to compare raw (uncorrected) REG sweat [Na+ ] and predicted WB sweat [Na+ ] to measured WB sweat [Na+ ]. Mean bias (±95% LOA) between raw REG sweat [Na+ ] and measured WB sweat [Na+ ] was 10(±20), 0(±19), 9(±20), 22(±25), 23(±24), 0(±15), -4(±18) mmol/L for the dorsal forearm, ventral forearm, upper arm, chest, upper back, thigh, and calf, respectively. The mean bias (±95% LOA) between predicted WB sweat [Na+ ] and measured WB sweat [Na+ ] was 3(±14), 4(±12), 0(±14), 2(±17), -2(±16), 5(±13), 4(±15) mmol/L for the dorsal forearm, ventral forearm, upper arm, chest, upper back, thigh, and calf, respectively. Prediction equations improve the accuracy of estimating WB sweat [Na+ ] from REG and are therefore recommended for use when determining individualized sweat electrolyte losses.

Keywords: electrolytes; heat stress; sweating rate; tattoos.

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Conflict of interest statement

All authors are employed by PepsiCo R&D. The views expressed in this manuscript are those of the authors and do not necessarily reflect the position or policy of PepsiCo, Inc.

Figures

Figure 1
Figure 1
Bland–Altman figures for dorsal forearm, ventral forearm, and ventral thigh
Figure 2
Figure 2
Bland–Altman figures for upper arm, chest, upper back, and calf
Figure 3
Figure 3
Summary of mean bias ±95% limits of agreement for all regions
Figure 4
Figure 4
Linear regression of regional vs. whole‐body sweat sodium concentration with regression lines for low and moderate relative humidity shown separately
See this image and copyright information in PMC

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