Servations indicate that augmented oxidative stress is abolished when vitamin C is given prior to several different types of interventions [37-39]. Furthermore, post-exercise FMD in the cuffed arm with prior vitamin C supplementation was similar to the control arm in PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/25957400 the placebo and vitamin C conditions, which indicates that NO bioavailability was unaffected. Finally, diet was not strictly controlled with our subjects; therefore dietary antioxidants may have varied between exercise sessions. To reduce this possible variation between sessions, our subjects fasted according to the latest dietary guidelines for FMD assessments [26] and were asked to maintain their normal dietary habits throughout the study.Our study has several limitations. FMD data following exercise should be interpreted with caution due to several vascular alterations (i.e. basal arterial diameter, sympathetic tone, blood flow and shear stress, and reactive hyperemia) which potentially contribute to the results [36]. In particular, significantly greater post-exercise baseline diameters in the cuffed arm may have artificially confounded the FMD results due to the mathematical bias against large baseline diameters. However, we did assess FMD as the absolute change from baseline to post-occlusion peak diameter and found identical results (data not shown). Also, smooth muscle function was not assessed before or after exercise; however manipulatedConclusion This study provides evidence that brachial artery flowmediated dilation is attenuated following lower body exercise with oscillatory and retrograde shear above the normal response, but the attenuation is not different across the applied gradations of retrograde shear which were imposed. We interpret these findings to indicate that augmented antegrade shear in the brachial artery during lower body aerobic exercise can partially override the negative influence of retrograde shear on postexercise flow-mediated dilation in the brachial artery by minimizing the increase of oscillatory shear. Furthermore, vitamin C supplementation prevented an attenuation of post-exercise flow-mediated dilation due to elevated retrograde shear during exercise. These data suggest that reactive oxygen species may contribute to the attenuation of brachial artery flow mediated dilation following lower body exercise with augmented brachial artery retrograde shear rate.Abbreviations eNOS: Endothelial nitric oxide synthase; BH4: Tetrahydrobiopterin; FMD: Flow-mediated dilation; SR: Shear rate; OSI: Oscillatory shear index; TTP: Time to peak.Competing interests The authors declare that they have no competing interests.Johnson et al. Cardiovascular Ultrasound 2012, 10:34 http://www.cardiovascularultrasound.com/content/10/1/Page 10 ofAuthors’ contributions BDJ was 1-Deoxynojirimycin site responsible for conception and study design, data collection, data analysis, statistical analysis and interpretation, and drafting the article. KJM assisted with study design, statistical interpretation, and revised the article for intellectual content. SCN contributed to study design, statistical interpretation, and revised the article for intellectual content. TDM participated in study design, statistical interpretation, and revised the article for intellectual content. JPW contributed to the development of the scientific question, study design, statistical interpretation, and revised the article for intellectual content. All authors read and approved the final manuscript. Acknowledgements We.