A thesis submitted to the University of Bedfordshire, in fulfilment of the requirements for the degree of MSc by ResearchAims The aim of this thesis was to explore the effects of interrupting prolonged sitting with high-intensity activity on cardiometabolic risk markers. Methods In study 1, participants completed 3, 8 hour trials: 1) uninterrupted sitting (SIT) 2) continuous moderate-intensity activity followed by sitting, and 3) sitting interrupted with hourly high-intensity activity (SIT-ACT). In study 2, participants completed 3, 6.5 hour trials: 1) SIT, 2) a continuous high-intensity interval exercise session followed by sitting (CON-HIE), and 3) sitting interrupted with high-intensity activity bouts (SIT-HIE). Postprandial incremental area under the curve (iAUC) was calculated for cardiometabolic risk markers and compared between conditions. Data are mean (95% confidence intervals). Results In study 1, glucose iAUC was not different between conditions (p= 0.606). Triglyceride (TG) iAUC was lower and high-density lipoprotein was higher in SIT-ACT than SIT (p=<0.05). In study 2, glucose iAUC was significantly lower in SIT-HIE than SIT (p=0.026), while TG iAUC was significantly lower in CON-HIE than SIT (p=0.014). Conclusion Study 1 observed beneficial TG and HDL responses to interrupting sitting with high-intensity activity. Study 2 observed suppressed glucose in response to interrupting sitting with high-intensity activity, but postprandial TG was reduced only in response to a high-intensity interval exercise session
