Sedentary behaviour and physical activity in adults: measurement and behaviour change

The increasing evidence of associations between sedentary behaviour and low levels of physical activity in adults and both immediate and long term health implications is of public health concern. There is a need to further our understanding of adult's health behaviours, to facilitate the development of behaviour change strategies promoting healthy behaviours. This thesis provides four independent but interlinked studies focusing on adult s sedentary behaviour and physical activity in the context of measurement and behaviour change. Chapter 1 provides an introduction to the thesis where the scene is set for the placement of the studies in this thesis in the field of sedentary behaviour, physical activity, and measurement methods. Chapter 2 describes a systematic review of the relationship between sedentary behaviour and physical activity in adults. This systematic review is of primary importance as it was instrumental in shaping and informing the direction of the research described in later chapters. Chapter 3 describes a laboratory study investigating the measurement of energy expenditure during common sitting and standing tasks and also examines the 1.5 MET definition of sedentary behaviour. This study provides evidence that the 1.5 MET threshold for sedentary behaviours seems reasonable however some sitting-based activities may be classified as non-sedentary in people of differing weight status. This study raised some important questions on the validity of objective measurement devices for differentiating between sitting and standing postures. Thus, Chapter 4 of this thesis describes a laboratory study investigating the validity of the ActiGraph inclinometer algorithms for differentiating between sitting and standing postures. Chapter 5 is an intervention investigating sedentary behavior and physical activity compensation outside working hours in a sample of office workers exposed to sit-to-stand desks in the workplace. This thesis found that light physical activity, especially standing, could be one of the most efficient and feasible behaviours to replace sedentary behaviour. Such findings add considerably to the existing literature. Targeting such facets of adults behaviour and specially office workers holds great potential for behaviour change strategies.