Suitability of Bioelectrical Based Methods to Assess Water Compartments in Recreational and Elite Athletes

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Objective: It is important for highly active individuals to easily and accurately assess their hydration level. Bioelectrical impedance (BIA) can potentially meet these needs but its validity in active individuals is not well established. We aim to validate total body water (TBW), extracellular water (ECW), and intracellular water (ICW) estimates obtained from 50 kHz BIA, bioelectrical impedance spectroscopy (BIS), and BIA-based models against dilution techniques in 2 populations: active adults and elite athletes.Methods: Active males (N = 28, 20–39 years) involved in recreational sports and elite athletes (females: N = 57, 16–35 years; males: N = 127, 16–38 years) participated in this study. TBW and ECW were assessed with deuterium and bromide dilution, respectively. ICW was assessed as their difference. Body water compartments were also assessed by BIA (BIA-101), BIS (model 4200), and BIA-based equations.Results: Small but significant differences were observed between alternative methods and the criterion in all subsamples. In female athletes, r2 > 0.69, r2 > 0.57, and r2 > 0.65 were observed between methods in the TBW, ECW, and ICW estimates. In males, r2 > 0.75, r2 > 0.65, and r2 > 0.68 were found between alternative and reference methods in the TBW, ECW, and ICW estimates, respectively, whereas for male recreational exercisers, r2 > 0.58, r2 > 0.73, and r2 > 0.75 were observed. Pure errors ranged between 0.19 to 3.32 kg for TBW, 0.64 to 1.63 for ECW, and 1.98 to 2.64 in ICW. The highest limits of agreement (LoA) were observed in Van Loan and Mayclin equation and the BIA method, respectively, for TBW and ECW assessment and the lowest LoA were observed in BIS for both TBW and ECW estimates.Conclusions: The higher accuracy of BIS in predicting individual TBW, ECW, and ICW highlights its utility in water assessment of recreational and elite athletes.