Effect of breaking up sitting with regular active breaks on glucose management and vascular function in adults with type 1 diabetes who use hybrid closed-loop insulin delivery systems: a randomised crossover trial protocol.

Sedentary behaviour is associated with an increased risk of cardiovascular disease and all-cause mortality in people with type 1 diabetes (T1D). Recent research has found that interrupting prolonged sitting with low-intensity activity acutely improves glycaemic management in people with T1D who use multiple daily insulin injections or continuous subcutaneous insulin infusion. However, the acute glycaemic effects of breaking up sitting with low-intensity walking on people with T1D using hybrid closed-loop (HCL) insulin systems are yet to be examined. The primary aim of the present study is to investigate the influence of breaking up 7 hours of sitting with 3 min intervals of low-intensity walking every 30 min on glucose management in individuals with T1D who use HCL systems. Adults with T1D (n=24), who use HCL systems, will complete two experimental conditions in this randomised cross-over trial. One condition will require sitting uninterrupted for 7 hours (Sedentary), while the other will require breaking up 7 hours of sitting with 3 min of low-intensity walking every 30 min (Active Breaks). During both conditions, interstitial glucose concentrations (via CGM) and insulin administration (via HCL) will be recorded throughout. In addition, peripheral vascular function (via flow-mediated dilation) and cerebral vascular function (via CO2 reactivity) will be measured at baseline and post. Data will be analysed using paired t-tests and analyses of variance. The trial has been approved in the UK by the London City and East Research Ethics Committee (25/PR/0098). The findings from the study will be disseminated through peer-reviewed journals and presentations at national and international scientific conferences. Trial registration number: ISRCTN56375691.