Investigating the relationship between habitual physical activity and cardiovascular health in healthy and clinical populations

Physical activity (PA) is beneficial for arterial and autonomic health and, subsequently, cardiovascular disease risk. However, fundamental questions remain regarding the relationship between PA and health, the relative importance of the volume, intensity or composition of PA, and whether this differs in chronic conditions. Therefore, the aim of this thesis was to explore the influence of movement behaviours on key cardiovascular risk factors in healthy populations and those with T1D using novel methods and analysis techniques. Chapter 4 revealed that, contrary to expectation, the composition of daily movement and sleep behaviours was not associated with arterial stiffness in healthy children, with the reallocation of time between any behaviours not predicting significant change in arterial stiffness. It was hypothesised that this may be related to the measurement duration being insufficient to reflect habitual PA and its health-associated fluctuations. Therefore, a 28-day measurement period was used in Chapter 5, which revealed that, whilst there was minimal fluctuation in movement behaviours, PA metrics derived from 28 days were more strongly associated with cardiovascular health markers. Using a similar measurement protocol, children with type I diabetes (T1D) were found to engage in more light and less moderate-to-vigorous physical activity (MVPA) than healthy peers and were characterised by poorer arterial stiffness and autonomic function (Chapter 6). Importantly, Chapter 6 suggested that the intensity of PA was more influential than the volume. Subsequently, Chapter 7 supported this contention, revealing that the reallocation of time from any behaviour to MVPA was the most potent stimulus to cardiovascular health in T1D. Overall, this thesis demonstrates that the composition and the relative importance of the volume and intensity of PA must be considered when investigating the relationship with health. The findings highlight key targets for future interventions seeking to enhance the cardiovascular function of youth, especially in T1D.