Urinary hydration biomarkers, but not renal blood velocity, are impacted by a 161-km ultra-endurance footrace
Authors: Linder Braxton A. , Stute Nina L. , Jeong Soolim , El-Kurd Omar B. , Vondrasek Joseph D. , Pasternak IV Andrew , Schlader Zachary 
Published: May 2024

PURPOSE: Recent data suggest that dehydration (i.e., increases in urine specific gravity (USG) and osmolality (OSM)) may contribute to increased risk of acute kidney injury (AKI) [1]. AKI may be transiently elevated in a substantial proportion of athletes upon completing ultra-endurance running events (42km) [2], indicating potential kidney strain via reductions in renal perfusion. However, there are limited data on the effects of ultra-endurance running events on renal blood velocity (RBV). Therefore, we sought to investigate the effects of the 2023 161-km Western States Endurance Run (WSER) on hydration biomarkers and RBV. We hypothesized that USG and OSM would be higher and that RBV would be lower post- versus pre-race. METHODS: We included 17 participants (3F/14M, 44±10yrs, 175±7cm, 69±9kg) with urine samples and RBV data in this analysis. We measured USG with a refractometer and OSM with an osmometer. We assessed RBV in the decubitus position using sonography at the renal and segmental arteries (GE Logiq e). Renal vascular conductance, the ease with which blood flows through kidney vasculature, was calculated as RBV/supine central mean blood pressure (SphygmoCor XCEL). Pre-race measures were collected ≤72 hours before WSER and post-race measures were collected ≤1 hour after finishing. Normality was assessed and paired, two-sided t-tests or Wilcoxon paired tests were used to compare pre- vs. post-race measures. Normalized differences were calculated ([pre-post]/pre) to assess associations between variables using Pearson’s correlation. We set α a priori to ≤ 0.05. Results: The WSER elicited an increase in USG (1.010±0.007 vs 1.026±0.011, p=0.002) and urine OSM (420±220 vs 740±305 mOsm/kg, p=0.003). However, RBV was unaffected post-race in the renal (49.3±10.0 vs 44.6±13.4 cm·s−1, p=0.285) and segmental artery (28.9±6.4 vs 27.5±1.6 cm·s−1, p=0.345). There were no differences in vascular conductance in the renal (0.55±0.10 vs 0.53±0.19 cm·s−1/mmHg, p=0.808) or the segmental artery (0.325±0.02 vs 0.325±0.02 cm·s−1/mmHg, p=0.903). No associations were observed between changes in RBV and changes in hydration biomarkers ( ps>0.243). CONCLUSIONS: We observed large elevations in USG and OSM, which may suggest a transient increase in workload within the kidneys, but no change in renal or segmental artery vascular conductance after WSER. Future analyses are needed to investigate whether AKI biomarkers may be elevated after the completion of ultra-endurance events, particularly among higher-risk runners. National Institutes of Health K01HL160772 (JCW), American Heart Association 23CDA1037938 (JCW), Western States Endurance Run Medical Research Program (GJG), NIH-K01HL147998 (ATR), Auburn University Offce of Vice President for Research Support Program (ATR). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.