Classic BIVA Differences by Position and Rugby-Specific Tolerance Ellipses in Collegiate Male Rugby Athletes

Bioelectrical impedance vector analysis (BIVA) supports interpretation of hydration and soft-tissue status, yet population reference ellipses may not reflect rugby union athletes. PURPOSE: Compare classic BIVA between forwards and backs and derive rugby-specific tolerance ellipses. METHODS: Twenty-one collegiate male rugby athletes (forwards n=15; backs n=6) completed standing multifrequency BIA (seca mBCA 514) in the morning after an overnight fast (≥12 h) and ≥24 h exercise abstention. Hydration was assessed via urine specific gravity (USG; CLINITEK Status+; Multistix 10 SG). Whole-body 50 kHz resistance (R) and reactance (Xc) were averaged bilaterally; |Xc| was used, values were normalized to height (R/H, Xc/H), and phase angle was calculated (arctan[Xc/R]·180/π). Groups were compared with Welch t-tests and mean vector displacement with Hotelling’s T² (α=0.05). Rugby-specific 50/75/95% tolerance ellipses were derived from the mean vector and covariance matrix. RESULTS: USG indicated 18/21 athletes were >1.020 and 14/21 were recorded as ≥1.030. Overall, R/H and Xc/H were 287.2 ± 42.5 and 33.4 ± 4.8 Ω/m, and phase angle was 6.7 ± 0.6°. Backs had higher R/H (331.7 ± 22.0 vs 269.4 ± 34.8 Ω/m, p