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Patterns of physical activity and sedentary behaviour and cardiovascular health in children Nettlefold, Lindsay Anne


Introduction: Physical activity (PA) and sedentary behaviours are important modifiable risk factors for cardiovascular disease in adults; however, we know much less about their role for enhancing and sustaining children’s cardiovascular health. The aim of this thesis is to evaluate the relation between PA, sedentary time, and cardiovascular health in children. Methods: Participants were volunteers in a two-year randomized controlled dissemination trial of a whole school PA model (30 schools; 1,529 children). Activity intensity was measured via accelerometry (n=629), arterial compliance by applanation tonometry (n=250), and cardiovascular fitness (CVF) using a 20-meter shuttle run test (n=1,319). Results: In study 1, epoch length influenced the volume of activity recorded; however, the direction and magnitude of the bias depended on activity intensity and volume. In study 2, girls accumulated less moderate-to-vigorous PA (MVPA) and more sedentary time compared with boys, except during physical education. Fewer girls than boys met PA guidelines during school, recess, and lunch. Similarly few boys and girls (< 3%) met PA guidelines during physical education. In study 3, PA was beneficially associated with small, but not large, artery compliance. Bouted MVPA was not associated with small or large artery compliance. In study 4, activity was associated with CVF in children. However, the association between bouted MVPA and CVF was not independent of total MVPA. In study 5, girls and boys randomized to intervention schools had 31-37% greater CVF at the end of year one compared with children attending control schools; the magnitude was clinically relevant, but not statistically significant after adjusting for school clusters. There was no betweengroup difference across year two. Conclusions: Objective measures of activity improve the relation between PA and cardiovascular health thus future research should standardize methods and use accelerometers to assess children’s activity whenever possible. Children undertake little PA during school, particularly during physical education. Whole school PA interventions may enhance the cardiovascular health of children; however, generalist teachers require training and support for sustained effects. Long term prospective trials of activity (assessed by accelerometry) and targeted PA interventions that control for school clusters would fill a notable gap in the paediatric literature.

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