Urine Specific Gravity Effect on Total and Segmental Body Composition Validity of Multifrequency Bioelectrical Impedance Analysis Compared With Dual Energy X-Ray Absorptiometry.

Fleck, SJ, Hayes, A, Stadler, G, Goesch, T, Goldammer, M, and Braun, S. Urine specific gravity effect on total and segmental body composition validity of multifrequency bioelectrical impedance analysis compared with dual energy x-ray absorptiometry. J Strength Cond Res 35(2): 373-384, 2021-The purposes were to compare body composition measures between a specific multifrequency bioelectrical impedance analyzer (InBody770) and dual-energy x-ray absorptiometry (DXA) and determine if hydration status within a specified range affected these measures. Methods included determining urine specific gravity before testing. Urine specific gravity needed to be within typical well-hydrated (n = 37), euhydrated (n = 45), or slightly dehydrated (n = 20) ranges. Segmental and total body composition measures were determined with the InBody770 and by DXA within the same testing session. Paired sample t-tests revealed significant differences (p < 0.005) between InBody770 and DXA for all body composition variables for all 3 hydration statuses, except for trunk fat-free mass (FFM) and trunk fat mass (FM) of the well-hydrated and euhydrated groups and right leg FM and trunk FFM of the slightly dehydrated group. For the total sample (n = 102), InBody770 significantly underestimated total body FM, right arm FFM, left arm FFM, right leg FFM, and left leg FFM with the range of underestimation being between 0.16 and 2.87 kg. The total body FFM by InBody770 was overestimated by 2.33 ± 2.80 kg or 3.6%. Bland-Altman plots supported these results. The major conclusions are that differences between the InBody770 and DXA segmental and total body FFM and FM are not significantly affected by hydration status in the range investigated, and the FM and FFM determined by the 2 devices are generally significantly different.