Validation of Bioelectrical Impedance Spectroscopy to Measure Total Body Water in Resistance-Trained Males.

The three-compartment (3-C) model of physique assessment (fat mass, fat-free mass, water) incorporates total body water (TBW) whereas the two-compartment model (2-C) assumes a TBW of 73.72%. Deuterium dilution (D₂O) is the reference method for measuring TBW but is expensive and time consuming. Multifre-quency bioelectrical impedance spectroscopy (BIS SFB7) estimates TBW instantaneously and claims high precision. Our aim was to compare SFB7 with D₂O for estimating TBW in resistance trained males (BMI >25kg/m²). We included TBW_BIS estimates in a 3-C model and contrasted this and the 2-C model against the reference 3-C model using TBW_D2O. TBW of 29 males (32.4 ± 8.5 years; 183.4 ± 7.2 cm; 92.5 ± 9.9 kg; 27.5 ± 2.6 kg/m²) was measured using SFB7 and D2O. Body density was measured by BODPOD, with body composition calculated using the Siri equation. TBW_BIS values were consistent with TBW_D2O (SEE = 2.65L; TE = 2.6L) as were %BF values from the 3-C model (BODPOD + TBW_BIS) with the 3-C reference model (SEE = 2.20%; TE = 2.20%). For subjects with TBW more than 1% from the assumed 73.72% (n = 16), %BF from the 2-C model differed significantly from the reference 3-C model (Slope 0.6888; Intercept 5.093). The BIS SFB7 measured TBW accurately compared with D₂O. The 2C model with an assumed TBW of 73.72% introduces error in the estimation of body composition. We recommend TBW should be measured, either via the traditional D₂O method or when resources are limited, with BIS, so that body composition estimates are enhanced. The BIS can be accurately used in 3C equations to better predict TBW and BF% in resistance trained males compared with a 2C model. [ABSTRACT FROM AUTHOR]