Ranadive, Sushant M.Weiner, Cynthia M.Eagan, Lauren E.Addison, OdessaLanders-Ramos, Rian Q.Prior, Steven J.This study was performed to determine whether prolonged endurance running results in acute endothelial dysfunction and wave-reflection, as endothelial dysfunction and arterial stiffness are cardiovascular risk factors. Vascular function (conduit artery/macrovascular and resistance artery/microvascular) was assessed in 11 experienced runners (8 males, 3 females) before, during and after a 50 km ultramarathon. Blood pressure (BP), heart rate (HR), wave reflection, augmentation index (AIx) and AIx corrected for HR (AIx75) were taken at all time points—Baseline (BL), following 10, 20, 30 and 40 km, 1 h post-completion (1HP) and 24 h post-completion (24HP). Flow-mediated dilatation (FMD) and inflammatory biomarkers were examined at BL, 1HP and 24HP. Reactive hyperaemia area under the curve (AUC) and shear rate AUC to peak dilatation were lower (∼75%) at 1HP compared with BL (P < 0.001 for both) and reactive hyperaemia was higher at 24HP (∼27%) compared with BL (P = 0.018). Compared to BL, both mean central systolic BP and mean central diastolic BP were 7% and 10% higher, respectively, following 10 km and 6% and 9% higher, respectively, following 20 km, and then decreased by 5% and 8%, respectively, at 24HP (P < 0.05 for all). AIx (%) decreased following 20 km and following 40 km compared with BL (P < 0.05 for both) but increased following 40 km when corrected for HR (AIx75) compared with BL (P = 0.02). Forward wave amplitude significantly increased at 10 km (15%) compared with BL (P = 0.049), whereas backward wave reflection and reflected magnitude were similar at all time points. FMD and baseline diameter remained similar. These data indicate preservation of macrovascular (endothelial) function, but not microvascular function resulting from the 50 km ultramarathon.en-USArticle