The effect of high-intensity interval exercise on glucose tolerance and insulin sensitivity in healthy and diabetic youth

Cardiovascular disease (CVD) and type two diabetes mellitus (T2D) are among the leading causes of death worldwide. Insulin resistance (IR) and hyperglycaemia are risk factors for CVD and T2D and are known to be prevalent in youth. Physical activity (PA) is known to improve IR and glucose tolerance in youth, but current levels of PA are low meaning alternative PA recommendations are needed. The purpose of this thesis is to investigate the effect of low volume high-intensity interval exercise (HIIE) on insulin and glucose health outcomes in male children and adolescents. Additionally, the thesis will explore the potential for HIIE to improve glycaemic control in paediatric patients with type one diabetes mellitus (T1D). Chapter 4 examines the relationship between estimates of insulin sensitivity (IS) based on oral glucose tolerance test (OGTT) and fasted assessment methods, in addition to the day-to-day reliability of these measures in children and adolescents. Results from this chapter advocated the Cederholm index to measure IS in this sample due to the low day to day reliability (coefficient of variation (%CV) of 6.4%). Chapter 5 demonstrates comparable results, reporting moderate improvements to IS and glucose tolerance measured via an OGTT 10 minutes after a single bout of HIIE and work-matched moderate-intensity exercise (MIE) in adolescent boys (13-15 y old). The findings from Chapter 5 are extended in Chapter 6, where changes to OGTT derived IS and glucose tolerance were measured up to 24 h post exercise and fasting measures of IS up to 48 h after exercise. Improvements to IS and glucose tolerance after the OGTT persisted for up to 24 h after HIIE and MIE, but no changes to fasting outcomes were observed over the 48 h period. In contrast to Chapter 5, Chapter 7 reports that a single bout of HIIE but not work-matched MIE resulted in only a small improvement in IS in 8-10 year old boys. Chapter 8 assesses the efficacy of 6 sessions of HIIE performed over 2 weeks to alter fasting and postprandial (mixed-meal tolerance test) insulin and glucose outcomes in adolescent boys. In contrast to acute exercise (Chapters 5 and 6), HIIE training over 2 weeks did not improve insulin and glucose outcomes in this population. Finally, Chapter 9 presents a case study on three adolescents with T1D to examine the effect of acute HIIE and MIE on glycaemic control. This study indicates that both MIE and HIIE have the potential to improve short-term (24 h) glycaemic control within this clinical population. Taken collectively, the studies from this thesis demonstrate that HIIE offers an effectual and feasible alternative to MIE to improve insulin and glucose health outcomes in healthy children and adolescents, and short-term glycaemic control in adolescents with T1D