This study was conducted to validate the relationship between bioelectrical conductance (ht2/R) and densitometrically determined fat-free mass, and to compare the prediction errors of body fatness derived from the tetrapolar impedance method and skinfold thicknesses, relative to hydrodensitometry. One-hundred and fourteen male and female subjects, aged 18-50 yr, with a wide range of fat-free mass (34-96 kg) and percent body fat (4-41%), participated. For males, densitometrically determined fat-free mass was correlated highly (r = 0.979), with fat-free mass predicted from tetrapolar conductance measures using an equation developed for males in a previous study. For females, the correlation between measured fat-free mass and values predicted from the combined (previous and present male data) equation for men also was strong (r = 0.954). The regression coefficients in the male and female regression equations were not significantly different. Relative to hydrodensitometry, the impedance method had a lower predictive error or standard error of the estimates of estimating body fatness than did a standard anthropometric technique (2.7 vs. 3.9%). Therefore this study establishes the validity and reliability of the tetrapolar impedance method for use in assessment of body composition in healthy humans.

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Determinations of total body water (TBW) calculated from deuterium dilution spaces and bioelectrical-impedance measurements were made serially in a group of 15 women before, during, and after pregnancy. Similar measurements were made once in a group of 50 nonpregnant women and intermittently in another group of 10 women during pregnancy and postpartum. TBW increased significantly during pregnancy, then decreased postpartum. Estimates of TBW in pregnancy and postpartum calculated with models derived from nonpregnant and pregnant women were similar to measured values. Changes in reactance and resistance explained more of the variance in predicting changes in TBW than did body weight, abdominal circumference, or hematocrit (50-75% vs 4-50%, respectively). Changes in TBW estimated with the nonpregnancy impedance model were significantly different than either the measured changes or changes predicted with the pregnancy impedance model. These findings indicate that the impedance method is a practical and valid method for determining longitudinal changes in TBW.