Exploring the role of exercise induced shear rate upon vascular health throughout the lifespan

Introduction: Deterioration in vascular health contributes to cardiovascular disease. Ageing is independently associated with poorer vascular health. Furthermore, the rate of decline in vascular health differs between genders. Exercise-induced shear rate (SR) is hypothesised to be an important stimulus for improvements in vascular health. How interval (IT) and continuous (CON) exercise affect patterns and volumes of SR to modify acute and chronic vascular health across the lifespan and between genders has not been explored. The overall aim of this thesis was to characterise in-exercise SR during IT and CON exercise and assess acute and chronic effect endothelial function and biomarkers of endothelial cell phenotype.
Methods: Ultrasound was used to determine acute and chronic endothelial function following exercise and the association with in-exercise SR. Circulating microRNA-21 expression both acutely and chronically was assessed as a biomarker of SR response. Firstly, 13 young healthy participants underwent 4 separate acute exercise sessions consisting of intensity and duration matched CON and IT exercise. Secondly, 16 younger and 11 older (males and females) participants underwent a 4-week training intervention comprising either CON or IT.
Results: Pattern of in-exercise SR followed the work rate profile of the exercise. Despite differing SR patterns there was no difference in volumes of anterograde and retrograde SR between protocols, with all exercise protocols inducing retrograde SR and brief periods of purely oscillatory SR, in the first study. Acute endothelial function increased and microRNA-21 expression decreased irrespective of exercise protocol. In the second study, IT induced greater volumes of retrograde SR compared to CON and decreased with training. Endothelial function improved acutely and chronically whilst chronic microRNA-21 expression increased following both IT and CON training irrespective of age or gender.
Discussion: In-exercise pattern of SR was driven by heart rate and blood flow. Pattern of SR differed between CON and IT exercise protocols in the second study only. However, all exercise protocols in both studies produced predominantly laminar SR resulting in equivalent improvements in acute and chronic endothelial function, with no influence of age or gender. MicroRNA-21 expression was differentially affected by acute and chronic exercise irrespective of protocol.