TEST-RETEST RELIABILITY OF BODY FAT PERCENTAGE RESULTS USING DUAL ENERGY X-RAY ABSORPTIOMETRY AND THE BOD POD

Abstract

This study was conducted to determine the test-retest reliability of body fat percentage (BF%) results obtained using Dual Energy X-ray Absorptiometry (DXA) and the Bod Pod (Pod) in 100 middle-age women (mean age: 40.4 years). Each subject was tested in a one-piece nylon swim suit and a lycra cap was worn in the Pod. Subjects were first tested in the Pod (Life Measurement Instruments) and then using DXA (Model 4500W, Hologic). For both measurement techniques, subjects were given a couple of minutes to stretch between the test and the retest. For the Pod assessment, lung volume was measured during the first test and then the same lung volume was used for the retest. Results showed that the test-retest findings were similar using DXA and the Bod Pod. Using DXA, the test and retest means were statistically equal (DXA 1: 30.29 ± 7.15 and DXA 2: 30.41 ± 7.33; mean difference: 0.12 ± 0.72, p > 0.05). the test-retest means were also statistically equal using the Pod (Pod 1: 30.84 ± 7.98, Pod 2: 30.77 ± 7.97; mean difference: 0.07 ± 1.33, p > 0.05). The mean of the sum of the absolute values of each test-retest difference was 0.41 and 0.81 using DXA and the Pod, respectively. The intraclass correlation between the two DXA tests was 0.999 and also 0.999 for the two Pod tests. Of the 100 subjects, 95 (95%) had less than 1% point difference between their first and second DXA tests. There were 75 subjects who had less than a 1% point difference for the Pod. Similarly, 75 subjects had less than 0.5% point difference between the test and retest using DXA, and 53 had less than 0.5% difference for the Pod. Clearly, dual energy x-ray absorptiometry and the Bod Pod methods of assessing BF% are extremely reliable, with the DXA method showing remarkable test-retest stability.