| Summary: | Background: Sedentary behaviour has emerged as an independent risk factor for unfavourable metabolic health outcomes, including Type 2 Diabetes Mellitus (T2DM). Through an acute experimental setting, it has recently been demonstrated that breaking up sitting time through short, regular light physical activity breaks (in the form of standing, walking and resistance exercise) can be an effective way to reduce postprandial glycaemia. In order to embark on a personalised approach to reducing sedentary behaviour, more information is required about how other health behaviours interact with it, and whether alternative modes of activity breaks can instigate glycaemic improvements. It is also apparent that little is known about the chronic glycaemic impacts of reducing sedentary time when accounting for other health behaviours, this warrants further exploration. Aims: 1. Design and conduct an experimental trial establishing the modifying impact of cardio‐respiratory fitness (CRF) on glycaemic responses to prolonged sitting and light activity breaks. 2. Design and conduct an experimental trial establishing whether breaking up sedentary time with activity breaks, while remaining in a seated posture, is an effective way to attenuate postprandial glycaemia in those at high risk. 3. Prospectively determine whether reductions in sedentary time are associated with long‐term glycaemic benefit in those at high risk when accounting for other health behaviours such as weight management and exercise. Key Findings: 1. Individuals with low CRF had worse glycaemic responses during prolonged sitting and gained the most metabolic benefit from light activity breaks. 2. Performing regular, short bouts of upper body activity during prolonged sitting effectively reduced postprandial glycaemia despite maintaining a seated posture. 3. Change in sedentary time was not significantly associated with change in HbA1c after adjustment for change in MVPA time. Conclusions: Efforts to tackle sedentary behaviour in the promotion of metabolic health may be optimised by tailoring to an individual’s CRF level. This and the notion that sitting per se may not be responsible for the metabolic downfalls of sedentary behaviour demonstrates potential for personalisation of strategies in those with contraindication to weight bearing activity. Future research directly extending acute trials through longer term interventions are necessary to truly elucidate whether glycaemic adaptations, such as a change in HbA1c, are evident from reductions in sedentary time over a prolonged period.
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