Intra-Individual Variability in Test-Retest Air Displacement Plethysmography Measurements of Body Density for Men and Women.
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Air displacement plethysmography (ADP) is a popular method for estimating body density (Db). Most ADP tests are performed once, with test-retest investigations scarce. Therefore, we investigated test-retest reliability of ADP. Active men (n=25) and women (n=25) volunteered and followed standard pre-test guidelines. Participants wore dry, form-fitting swimwear and manufacturer-supplied swim caps. In a single session, two ADP trials with measured thoracic gas volume (TGV) were performed without repositioning participants. Separate 2 (sex) x 2 (ADP trial) repeated-measures ANOVAs were performed to investigate within-between comparisons of Db, TGV, body volume (Vb), and relative fatness (%BF). Paired t-tests were used to investigate significant differences as appropriate. The Bland and Altman technique was used to depict individual intra-trial variations. For all analyses, α=.05. A significant main effect for sex was found; men were lower in %BF and higher in all other variables compared to women. Individual variability was notable (ADP1-ADP2). The range of individual inter-trial differences were larger for women than men, respectively, for Db (-0.0096 to 0.0045 g/cc; -0.0019 to 0.0054 g/cc), TGV (-0.623 to 1.325 L; -0.584 to 0.378 L), Vb (-0.249 to 2.10 L; -0.234 to 0.397 L), and %BF (-2.1 to 4.4 %; -0.2 to 0.9 %). When assessing body composition of women via ADP or using Db from ADP in a multicomponent model, at least two trials with measured TGV should be performed and the average of the values recorded and reported.