Early-onset type 2 diabetes: nerve function, impacts of high-intensity interval training, and exercise program acceptability

Diabetes is recognised as the world’s fastest growing chronic condition. The prevalence of early-onset type 2 diabetes (diagnosed with type 2 diabetes before the age of 45 years) has risen sharply over the past decades, with lack of physical activity and excessive sedentary behaviour being important contributing factors. Early-onset type 2 diabetes is associated with earlier onset of diabetes-related complications, including diabetic peripheral neuropathy and brachial arterial stiffness. Exercise is a well-established, first-line management strategy for type 2 diabetes, but there is limited high quality research on whether people with early-onset type 2 diabetes respond to exercise in the same way as people with late-onset type 2 diabetes. The aim of this thesis was to investigate the impact of high-intensity interval training (HIIT) on nerve function, endothelial function, aerobic fitness, physical activity, quality of life, and attitude to exercise through the use of qualitative and quantitative methodologies in people with early-onset type 2 diabetes. The thesis also examined how people with early-onset type 2 diabetes differed (at baseline) from matched controls without diabetes in the above outcome measures. The first study in the thesis is a systematic review (Chapter 2), that demonstrated aerobic exercise can be effective in improving nerve function in people with type 2 diabetes. The second study in the thesis is a pilot randomised controlled trial. (Chapters 3, 4) An eight-week HIIT program was carried out among eleven people with early-onset type 2 diabetes. The study found participants had significant improvement in aerobic fitness after the HIIT program, with little change in glycated haemoglobin, nerve function, endothelial function, physical activity, attitude to exercise, or quality of life. The qualitative component of the study identified many barriers that hindered participants’ engagement in diabetes services and regular exercise, and revealed a boom bust exercise history. A cross-sectional study (Chapter 6, 7) compared participants with early-onset type 2 diabetes to age-, gender-, ethnicity- and body mass index-matched control participants without diabetes. There was no significant difference between the two groups in nerve function and aerobic fitness. HbA1c was significantly correlated with a variety of nerve and anthropometric measures, and VO2peak was significantly correlated with a variety of nerve and endothelial function outcome measurements. Participants with early-onset type 2 diabetes demonstrated lower level of physical activity and autonomous regulation (a component of self-determination theory) of exercise engagement when compared to control participants. Level of physical activity was correlated with autonomous regulation. Overall, the findings from this thesis demonstrated HIIT was safe, feasible and acceptable to offer to people with early-onset type 2 diabetes who had no pre-existing complications. A behavioural intervention might be needed to promote long-term exercise engagement and maintenance. Other impacts of HIIT in this cohort need to be confirmed by larger trials including people with different severity of complications