| Summary: | A high level of sedentary behaviour has recently emerged as a distinct risk factor for a number of diseases. On the other hand, a large body of evidence has shown that physical activity (PA) can prevent several illnesses. However, there are important issues regarding the accurate measurement of SB behaviour and physical activity in observational studies which are currently unresolved. Research is particularly needed to investigate the impact of characteristics of sedentary behaviour such as type/context, sedentary bout length, breaks in sedentary time on metabolic responses and accurate quantification of PA and SB is needed to evaluate current and changing physical activity and sedentary behaviour levels on health outcomes. A number of studies have demonstrated that replacing sedentary time with light-intensity physical activity such as standing can induce a measurable metabolic benefit. However, it is unclear whether these benefits could be stimulated by simply breaking up time spent sitting down by standing up, or whether the number of transitions from sitting to standing influences metabolic changes over and above the effects of total time spent standing. The first experimental study in this thesis demonstrated, in ten overweight/obese men, that prolonged standing – where participants alternated 15 minutes of sitting with 15 minutes of standing – energy expenditure was 10.7% higher than continuous sitting (p < 0.001) over an 8-hour observation period. Intermittent standing – where participants undertook 10, 1.5-minute bouts of standing in every half-hour – led to a further increase in energy expenditure of 9.0% (p < 0.001). Participants oxidised 7.1 g more fat and 7.7 g more carbohydrate with intermittent standing compared with prolonged standing, but there was no significant effects of either prolonged or intermittent standing breaks on postprandial incremental glucose, insulin or triglyceride (TG) responses.
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