Physical Activity, Sedentary Behaviour, and Health in Children and Youth
Mark, Amy Elizabeth
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There is currently a dearth of information suitable for the development of evidence-based physical activity and screen time guidelines for children and youth. The overarching purpose of this thesis was to generate findings that could be used to inform public health recommendations for physical activity and screen time. A series of six manuscripts were completed to explore the relationship between physical activity, sedentary behaviour, and health in youth. The first manuscript examined the dose-response relation between objectively measured total and moderate-to-vigorous physical activity with blood pressure and hypertension. Participating in 30 and 60 minutes of moderate-to-vigorous physical activity per day decreased the odds of hypertension in youth by 50% and 63%, respectively. The second manuscript explored the influence of intensity of physical activity and incidental movement on total and trunk adiposity. Moderate-to-vigorous intensity physical activity was found to predict total and trunk adiposity beyond other intensities and incidental movement. The third manuscript sought to determine whether or not physical activity accrued in bouts was more beneficial than total physical activity with relation to being overweight. The inclusion of short and medium-to-long bouts of physical activity decreased the odds of overweight above and beyond total physical activity level. The fourth manuscript included a detailed examination of the relation between physical activity and screen time by considering different forms of physical activity, different physical activity environments, and various screen time behaviours. By and large, physical activity and screen time were not related. The fifth manuscript determined the proportion of Canadian youth meeting screen time guidelines. Only 18% of girls and 14% of boys in grades 6 to 10 met screen time guidelines of no more than 2 hours per day. The final manuscript examined the relationship between screen time and metabolic syndrome. A dose-response relation was observed between screen time and metabolic syndrome independent of physical activity level. It is hoped that the findings from this thesis will provide useful information that will be considered in developing and modifying physical activity and screen time recommendations for the paediatric population.