Hydration Status Is Associated With Biomechanical Fatigue During A 20 km Run

Hypohydration may impair endurance performance; however, it is unclear what effect baseline hydration status and changes in hydration status over time have on biomechanics during endurance running activities. PURPOSE: To quantify the relationship between baseline hydration status and changes in hydration with biomechanical outcomes across a 20 km run in recreational endurance runners. METHODS: 20 recreational runners (age: 36.9 + 13.1 years; BMI: 22.0 + 2.6 kg/m2; VO2 max: 51.38 + 9.1 mL/kg/min; sex: 10 M/10 F) completed a 20 km run at a self-selected pace on a standardized outdoor route (n = 10) or treadmill (n = 10). Participants wore shoe-mounted sensors to track contact time, pronation excursion and velocity metrics, shock, and cadence during the run. Pre-run urine samples were analyzed for osmolality to establish baseline hydration status, and post-run samples were taken to determine osmolality changes. General linear models were used to assess relationships between osmolality at baseline and pre-post osmolality change with biomechanics across each 5 km segment of the run. Run environment and temperature were included as covariates. RESULTS: Contact time was significantly longer in the final 5 km compared to the first 5 km but not significantly related to osmolality (p > 0.05). Lower baseline hydration status (i.e., higher osmolality) was significantly associated with increased pronation metrics in the final 10 km (p: 0.047-0.50; Table) and shock in the final 5 km (p = 0.02; Table). Greater changes in osmolality had significant positive associations with pronation metrics in the final 10 km (p: 0.005-0.04; Table). CONCLUSIONS: Increased pronation metrics were associated with lower baseline hydration status and greater changes in hydration during an endurance run. Maintaining adequate hydration prior to and during long distance runs may help mitigate biomechanical changes beyond 10 km. This study received funding from Samsung.