Physiological Reports (Aug 2020)
Cross‐validation of equations to predict whole‐body sweat sodium concentration from regional measures during exercise
Abstract
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.
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