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.
Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.