P. MUNTEAN*, A. PETRAŞ*, SANDRA POPA*, IRINA SIMA*, B. GLIȘICI*, O. CÎRJA*, F. SCHICK*, A. NEAGU*,**, OANA MUNTEANU*, V. PUPĂZAN*, MONICA NEAGU*#
*Discipline of Biophysics, Department of Functional Sciences, ”Victor Babeș” University of Medicine and Pharmacy, Timișoara, Romania
**Department of Physics & Astronomy, University of Missouri, Columbia, U.S.A.
Air displacement plethysmography (ADP) evaluates body fat percentage (%BF) by measuring body mass (BM) and body volume (BV). ADP performed by the BOD POD  demonstrated excellent repeatability, with a technical error of measurement (TEM) of the order of 1 %BF. Repeated measures protocols were proposed for spotting unreasonable results, as well as for improving overall reliability. One such protocol asks to perform at least two consecutive ADP tests and take their mean if they differ by at most 1 %BF; otherwise, perform a third test and take the mean of the two closest %BF values. Such a protocol was found to significantly improve the reliability of body composition assessments in middle-aged women. Nevertheless, a study of the BOD POD’s reliability indicated that BM underwent a statistically significant drop between two consecutive tests. A steady loss of BM of the order of 10 g/h is mainly attributed to pulmonary and cutaneous evaporation. Therefore, the drop of BM between successive tests might cause a systematic error in %BF assessments by repeated measures protocols of ADP. The present study aims to assess this error and to compare it to the TEM of %BF estimates using the BOD POD. Our study was performed on a highly heterogeneous sample of 65 healthy adults (38 men and 27 women), aged 18–49 years, who spanned a wide range of BV (41–130 L) and BMI (16.2–41.5 kg/m2). We performed two successive BOD POD tests for each subject and calculated the rate of change in body mass, obtaining –68±59 g/h. Since, on the average, one test lasted about 10 minutes, we estimated that the mean drop in body mass between two consecutive tests was of about 11 g, causing an increase in the measured %BF of the order of 0.1%. To further evaluate the impact of pulmonary and cutaneous evaporation on the results of repeated BOD POD measurements, we also performed a Bland-Altman analysis by plotting the differences vs. the means of BM, BV, and %BF values recorded in two successive tests. In conclusion, the errors caused by loss of body mass between consecutive measurements are about an order of magnitude smaller than the TEM of %BF assessments via ADP.
Key words: BOD POD reliability, body fat percentage, technical error of measurement.
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