A Comparison of Air Displacement Plethysmography and Bioimpedance Estimates of Body Composition in Young Adults

Abstract

PURPOSE: To examine the degree of agreement between body composition measures obtained via air displacement plethysmography (ADP) and leg-to-leg bioimpedance analysis (BIA) in a group of college-aged men and women. METHODS: ADP and BIA assessments of body composition were performed on twenty-one males (20.6 ± 2.19 years) and twenty females (20.9 ± 2.94 years). Body density (Db) values derived via ADP were converted to percent body fat (%BF) using the Brozek equation. The “standard adult” setting was used for deriving %BF estimates with the BIA instrument. RESULTS: Linear regression analyses indicated good correlation between the two measurement methods (r = .922, .746, and .863 for females, males, and for the pooled subject sample). However, standard error of estimate (SEE) values for females, males, and pooled subjects were 3.56%, 4.76%, 4.58%, thus exceeding 3.5% in all cases. %BF means for males (BIA: 19.67 ± 6.96%; ADP: 21.60 ± 9.34%) did not differ significantly between the two methods, but BIA significantly underestimated %BF as determined by ADP for females (BIA: 28.0 ± 8.94%; ADP: 32.0 ± 8.04%) and for the pooled sample (BIA: 23.7 ± 8.94%; ADP: 26.7 ± 10.10%). Bland-Altman analyses of the %BF data for males, females, and pooled subjects indicated no systematic bias, and also showed that 39 of 41 subjects' data fell within the 95% limits of agreement (mean difference ± 2 SD). However, the bands denned by the 95% confidence limits were broad, with the difference between %BF estimates exceeding 5% in 16 out of 41 subjects. CONCLUSIONS: Within the subject population we tested (non-athletic college-aged males and females), estimates of %BF from ADP and leg-to-leg BIA should not be considered to be interchangeable. Because neither ADP nor BIA provides a true criterion measure of %BF, these data do not permit a true evaluation of the criterion validity of these methods. This research was supported by a Jump-Rope-for-Heart Grant from the Illinois Association for Health, Physical Education, Recreation, & Dance.