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

The relationship of whole-body electrical resistance (WBR) to fat-free mass, derived from densitometry (FFM_Db ), hydrometry (FFM_TBW ), and densitometric fat-free mass corrected for hydration (FFM_D+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 FFM_Db , FFM_TBW , and FFM_D+W (r = 0.97, 0.95, and 0.97, respectively). Multiple regression analysis was employed to develop prediction equations for FFM_Db , FFM_TBW , and FFM_D+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 R² s to 0.95, 0.94, and 0.96 and decreasing the SEEs to 2.6, 3.2, and 2.5 kg, for FFM_Db , FFM_TBW , and FFM_D+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.