The Predictive Role of Raw Bioelectrical Impedance Parameters in Water Compartments and Fluid Distribution Assessed by Dilution Techniques in Athletes

The aims of this study were to analyze the usefulness of raw bioelectrical impedance (BI) parameters in assessing water compartments and fluid distribution in athletes. A total of 202 men and 71 female athletes were analyzed. Total body water (TBW) and extracellular water (ECW) were determined by dilution techniques, while intracellular water (ICW) was calculated. Fluid distribution was calculated as the ECW/ICW ratio (E:I). Phase angle (PhA), resistance (R) and reactance (Xc) were obtained through BI spectroscopy using frequency 50kHz. Fat (FM) and fat-free mass (FFM) were assessed by dual-energy X-ray absorptiometry. After adjusting for height, FM, FFM, age and sports category we observed that: PhA predicted ICW (females: beta = 1.62, p < 0.01; males: beta = 2.70, p < 0.01) and E:I (males and females: beta = 0.08; p < 0.01); R explained TBW (females: beta = 0.03; p < 0.01; males: beta = 0.06; p < 0.01) and ECW (females: beta = -0.02, p < 0.01; males: beta = 0.03, p < 0.01) and ICW (females: beta = -0.01, p < 0.053; males: beta = -0.03 p < 0.01); and Xc predicted ECW (females: beta = 0.06, p < 0.01; males: beta = 0.12, p < 0.01). A higher PhA is a good predictor of a larger ICW pool and a lower E:I, regardless of body composition, age, height, and sports category. Lower R is associated with higher water pools whereas ECW expansion is explained by lower Xc. Raw BI parameters are useful predictors of total and extracellular pools, cellular hydration and fluid distribution in athletes.