Association of bioelectrical resistance with estimates of fat‐free mass determined by densitometry and hydrometry

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Abstract
The relationship of whole‐body electrical resistance (WBR) to fat‐free mass, derived from densitometry (FFMDb), hydrometry (FFMTBW), and densitometric fat‐free mass corrected for hydration (FFMD+W) was investigated in three independent samples (AZ, IL, CA). Subjects included 75 males and 75 females ranging in age from 18 to 32 years. Whole‐body resistive index (WBRI) computed as height2/resistance was highly correlated to FFMDb, FFMTBW, and FFMD+W (r = 0.97, 0.95, and 0.97, respectively). Multiple regression analysis was employed to develop prediction equations for FFMDb, FFMTBW, and FFMD+W. In each prediction equation, WBRI was the single best predictor. Accounting for sex and variation in body weight significantly improved the prediction equations, by increasing the R2s to 0.95, 0.94, and 0.96 and decreasing the SEEs to 2.6, 3.2, and 2.5 kg, for FFMDb, FFMTBW, and FFMD+W, respectively. Similarity of the SEEs between methods (less than 1.0 kg difference) suggests consistency in the precision of WBRI estimates for body composition.