Leg fat-free mass and inter-limb leg fat-free mass asymmetry comparisons between bioelectrical impedance analysis and dual-energy X-ray absorptiometry in male career firefighters

The purpose of this study was to compare dominant and non-dominant leg fat-free mass (FFM) estimations and inter-limb leg FFM asymmetry detection between multi-frequency bioelectrical impedance analysis (MF-BIA) and dual-energy X-ray absorptiometry (DXA) in career firefighters. Sixty-one male career firefighters (age = 31.9 ± 7.4 years; stature = 179.0 ± 7.6 cm; body mass = 89.9 ± 17.4 kg) volunteered for the investigation and reported to the laboratory on one occasion. Leg FFM was estimated by measuring the conduction impedance measured through the corresponding sensing and injecting electrodes for MF-BIA and by outlining both legs into regions of interest for DXA. Inter-limb leg FFM asymmetry was calculated by subtracting the non-dominant limb FFM from the dominant limb FFM, dividing it by the dominant limb FFM, and expressed as a percentage. Asymmetry was defined as having inter-limb leg FFM asymmetry of ±3%. Paired sample <i>t</i> tests were used to examine differences in dominant and non-dominant limb FFM estimates and the McNemar's test was performed to compare inter-device frequencies of asymmetry detection. An alpha level of 0.05 was utilized a priori to determine statistical significance. Results indicated that MF-BIA significantly underestimated FFM for both the dominant (mean difference = 2.00 kg; <i>P</i> < 0.001) and non-dominant (mean difference = 1.97 kg; <i>P</i> < 0.001) limbs compared to DXA. Additionally, MF-BIA detected significantly (<i>P</i> = 0.004) fewer cases (two) of inter-limb leg FFM asymmetry when compared to DXA (12-cases). Although MF-BIA may be a practical field assessment to track whole-body and segmental-body compositional changes over time, it may not be as sensitive as DXA to identify inter-limb leg asymmetries in career firefighters.