From runner bean to couch potato: youth, inactivity and health

There is a growing public health concern over the effects that sedentary lifestyles are having on the health of young people, particularly in relation to overweight and obesity. This thesis presents five studies which examine the prevalence, incidence and determinants of sedentary behaviour among youth. The rationale for eachs tudy derives from a framework of behaviourale. pidemiology applied to physical activity and health. Study I presents four systematic reviews of literature. The first review presents a descriptive epidemiology of youth sedentary behaviour. The second review presents a summary of empirical correlates of television viewing, the most prevalent sedentary behaviour among young people. 'Me third and fourth reviews present quantitative syntheses of empirical relationships between television viewing and body composition (review 3) and sedentary behaviour and physical activity (review 4). Study 2 examines the prevalence and interrelationships among different sedentary behaviours and physical activity in a cross-nationa(l USA & UK) sample of 2,494 youth ages 11-15. Study 3 uses a qualitative strategy to generate a grounded framework from which to understand the choices young people make about how to spend their free-time. Study 4 adopts a micro-behavioural approach for understandingt he incidence and temporal patterning of sedentary behaviour among 162 adolescents (age 13-16). Study 5 presents an evaluation of a behaviour change theory useful for increasing levels of physical activity and reducing sedentary behaviour. Sedentary behaviour and physical activity do not appear to be two sides of the same coin and appear to have different sets of determinants. This is an important finding becausee fforts to increase levels of physical activity may not reduce levels of sedentary behaviour. While television viewing, video games and computer use are consistent referents in the academic and media panic surrounding youth inactivity, it is unlikely that these behaviours play a substantialr ole in epidemiologic trends of adolescent overweight and obesity. Further study should attempt to examine how contemporary lifestyles contribute to the growing prevalence of overweight and obesity among adolescents.