The influence of exercise intensity on vascular health outcomes in adolescents

Abstract

Cardiovascular diseases (CVD) are the leading cause of death, and the underlying atherosclerotic process has its origin in youth. Physical activity lowers future CVD risk, however few adolescents achieve the recommended minimum amount of daily activity and interventions fail to meaningfully increase activity levels in this group. It is therefore essential to identify how small volumes of exercise can be optimised for the primary prevention of CVD. The purpose of this thesis is to identify the influence of exercise intensity on vascular health outcomes in adolescents, and to assess the efficacy of 2 weeks of low volume, high-intensity interval training on CVD risk factors in this population.

Chapter 4 demonstrates that a single bout of high-intensity interval exercise (HIIE) performed one hour before a high fat meal elicits comparable reductions in postprandial lipaemia as a work-matched bout of moderate-intensity exercise (MIE) in girls. However, neither exercise attenuated postprandial lipaemia in the boys. Additionally, HIIE elicited a superior increase in postprandial fat oxidation and decrease in blood pressure, and this was sex independent. These findings are furthered in Chapter 5, which identified that accumulating HIIE, but not MIE, favourably modulates glycaemic control, postprandial blood pressure and fat oxidation in adolescents irrespective of sex.

A high fat meal was included in Chapter 6 in order to impair vascular function via oxidative stress. Postprandial vascular function was preserved following MIE, but improved after HIIE, and these changes were not related to changes in postprandial lipaemia or total antioxidant status. Chapter 7 addressed the time course of the changes in vascular function post exercise, and identified that HIIE promotes superior changes in vascular function than MIE.

Finally, Chapter 8 identified that 2 weeks of high-intensity interval training improved novel (endothelial function and heart rate variability), but not traditional CVD factors in adolescent boys and girls. However, most of these favourable changes were lost 3 days after training cessation.

Thus, this thesis demonstrates that vascular health outcomes are positively associated with exercise intensity. Given that HIIE was perceived to be more enjoyable than MIE in Chapters 4, 6 and 7, performing HIIE appears to be an effectual and feasible alternative to MIE for the primary prevention of CVD.