Agreement of Seca 286 Scale Weight with DXA Acquisition Weight, APEX Soft-Tissue Mass, and DXA Sum-of-Components Mass in Collegiate Rugby Athletes

Accurate body mass is foundational for DXA-derived indices and longitudinal tracking. PURPOSE: Determine agreement between Seca 286 scale weight and DXA acquisition weight, quantify the difference between DXA acquisition weight and the APEX whole-body mass field (fat + lean), and evaluate a DXA sum-of-components mass (fat + lean + BMC) relative to scale weight as an internal QC check (Houtkooper et al., Am J Clin Nutr, 2000). METHODS: Twenty-one male rugby union athletes completed same-morning testing (06:00–09:00 h) while fasted and post-void; caffeine was restricted (≥12 h) and exercise abstained (≥24 h). Hydration was screened prior to DXA. Body mass was measured in light clothing using a Seca 286 ultrasonic station (kg; 0.01-kg resolution) verified via manufacturer calibration check. Whole-body DXA was performed on Hologic Horizon W (APEX v5.6.1.3 rev 007); standard tissue analysis; daily QC within tolerance). DXA weight (kg) was entered from the same Seca 286 within 5 min of the DXA scan (no repeat weigh-ins). APEX exported whole-body mass equals the sum of whole-body fat and lean fields; a sum-of-components mass was computed as fat + lean + BMC. Paired comparisons, Pearson r, ICC(2,1), and Bland–Altman bias/limits of agreement (LoA) were computed. RESULTS: Seca 286 weight (91.48 ± 23.40 kg) was slightly lower than DXA acquisition weight (91.68 ± 23.42 kg) by -0.20 ± 0.13 kg (LoA -0.46 to 0.07 kg), with excellent agreement (r=0.99998; ICC=0.99995). The APEX whole-body mass field (fat + lean) was -1.98±1.02 kg lower than acquisition weight (LoA -3.98 to 0.03 kg). The DXA sum-of-components mass (fat + lean + BMC) was 1.43 ± 0.86 kg higher than Seca weight (LoA -0.25 to 3.12 kg; r=0.99946; ICC=0.99745). CONCLUSION: Under standardized conditions, Seca 286 and DXA acquisition weights show near-identical agreement; however, DXA mass fields differ by definition (soft tissue vs soft tissue+BMC) and can introduce systematic offsets. Investigators should pre-specify and consistently use the same mass variable when computing DXA-derived indices or tracking change over time.