Urine Specific Gravity Is Not Associated with Bioimpedance-Derived Total Body Water in Collegiate Rugby Athletes

Collegiate rugby athletes often report inadequate fluid intake, yet their large body size yields high absolute total body water (TBW). PURPOSE: To examine relationships between urine specific gravity (USG) and bioimpedance-derived TBW and extracellular water (ECW) during T1 testing in male collegiate rugby players. METHODS: Twenty-one male collegiate rugby athletes provided a first-morning, midstream clean-catch urine sample upon arrival (06:00-09:00 h) following an overnight fast; caffeine was restricted for 12 h and fluid intake was ad libitum. Urine specific gravity (USG; semi-quantitative strip output) was assessed via Siemens CLINITEK Status+ with Multistix 10 SG; urine color was recorded. Total body water (TBW, L) and extracellular water (ECW, L) were estimated via multi-frequency segmental bioelectrical impedance analysis (seca mBCA 514) in barefoot standing position; metal/jewelry were removed, manufacturer calibration procedures were followed, participants voided within 30 min, and refrained from exercise for 24 h. Hydration status was classified as euhydrated (USG ≤1.020) or hypohydrated (USG >1.020) per ACSM criteria. Associations were evaluated with Pearson correlation (α=0.05). RESULTS: Mean USG was 1.027±0.006, TBW 51.6±8.8 L, ECW 20.4±3.8 L, and ECW/TBW 39.5±1.1%. Urine color was recorded as clear yellow for all participants. Hypohydration prevalence was 86% (18/21), with 67% (14/21) exhibiting USG ≥1.030. USG was not associated with TBW (r=0.12, p=0.596), ECW (r=0.13, p=0.573), ECW/TBW (r=0.10, p=0.670), or TBW/ECW (r=-0.10, p=0.674). CONCLUSION: Dipstick-derived USG indicated frequent urine concentration despite standardized testing conditions but was not related to BIA-derived TBW or fluid compartment indices, suggesting USG and BIA-derived water measures capture distinct hydration constructs in collegiate rugby athletes.