INTRODUCTION OF A NOVEL HOME-BASED HIGH-INTENSITY INTERVAL TRAINING PROGRAMME TO IMPROVE CARDIO-METABOLIC HEALTH IN AT-RISK INDIVIDUALS

Abstract

New strategies are urgently needed to increase physical activity participation in the increasingly sedentary population to combat the rising rates of obesity and metabolic disease. The aim of this thesis was to provide evidence that practical high-intensity interval training (HIT) strategies can remove many of the major exercise barriers for obese individuals and people with type 1 diabetes that could potentially increase physical activity participation. Secondly, this thesis aimed to provide mechanistic evidence to explain the physiological effectiveness of HIT as a means to reduce the risk of cardio-metabolic disease. In Chapters 4 and 5, 32 obese adults with at least 3 additional cardiovascular disease (CVD) risk factors completed one of three 12-week training programmes 3x/week: Home-HIT (n=9); Laboratory-based supervised HIT (Lab-HIT; n=10) or home-based moderate intensity continuous training (Home-MICT; n=13). Changes in V O2peak, insulin sensitivity, body composition, flow-mediated dilation (FMD) and aortic pulse wave velocity (PWV) were assessed. Muscle biopsies were taken to assess changes in capillarisation, mitochondrial density, intramuscular triglyceride (IMTG) content and eNOS and GLUT4 protein expression using quantitative immunofluorescence microscopy. Adherence and compliance (Home-HIT 96±3% & 99±1%; Home-MICT 88±4% & 100±0%; Lab-HIT 97±1% & 100±0%, respectively) to training did not differ between groups. Training increased V O2peak and Matsuda insulin sensitivity index (P<0.05). BMI, body fat percentage and visceral fat decreased (P<0.05). FMD increased and aortic PWV decreased in each group (P<0.05). Immunofluorescence microscopy revealed increased capillarisation, mitochondrial density, IMTG content and eNOS and GLUT4 protein expression (P<0.05). In Chapter 6, 14 people with type 1 diabetes completed a randomised counterbalanced crossover design whereby continuous glucose monitoring was used to assess glycaemic control and risk of hypoglycaemia following a single bout of HIT and moderate-intensity continuous training (MICT) on separate days, compared to a non-exercise control day (CON). In Chapter 7, 14 people with type 1 diabetes (n=7 per group) completed six weeks of HIT or MICT 3x/week and the effect on glucose control and markers of cardio-metabolic health were measured. Chapter 6 showed no difference in the time, incidence or severity of hypoglycaemia over the 24-hour or nocturnal period between the CON, HIT and MICT days. In Chapter 7, six weeks of HIT or MICT improved V O2max by 14% and 15%, respectively and aortic PWV by 12%, with no difference between groups. Therefore, Chapters 6 and 7 demonstrate that HIT is an effective exercise strategy for people with type 1 diabetes that reduces the two major barriers of lack of time and fear of hypoglycaemia. Finally, in Chapter 8, eleven previously sedentary individuals with type 1 diabetes completed 6 weeks of Home-HIT. Blood glucose was monitored before, immediately and 1h after all of the exercise sessions. Perceptions of the program along with attitudes towards exercise, barriers to exercise and previous experiences of exercise were evaluated using an online survey. Training session adherence was 93±2%, with participants achieving their target HR in 99±1% of sessions. Blood glucose was not different from baseline immediately or 1h post HIT exercise. Training increased V O2peak by 8% (P=0.015), but blood pressure was unchanged (P=0.445). The qualitative data showed that the Home-HIT programme was positively received with many benefits. In conclusion, this thesis provides strong evidence that HIT can reduce major barriers to exercise and potentially increase exercise participation in these at-risk populations. Furthermore, Home-HIT was shown to be an effective strategy to improve a wide range of physiological markers indicative of improved cardio-metabolic health. Importantly, Home-HIT not only reduced traditional barriers to exercise, but also the key barrier in people with type 1 diabetes, fear of hypoglycaemia. As such, Home-HIT may represent an effective strategy to improve health in obese individuals with elevated CVD and people with type 1 diabetes by increasing exercise participation. Future research should investigate the effects of Home-HIT on a larger scale using larger cohorts and longer training periods using large-scale randomised controlled trials.