The Effects of Brief Supramaximal Exercise on Maximal Aerobic Capacity

Abstract

Non-communicable diseases (NCDs) are the leading cause of death worldwide. Physical inactivity is a risk factor of NCDs. Although exercise recommendations have been made, many people do not meet these criteria. Lack of time is one of the main perceived exercise barrier. To address this barrier, more time-efficient exercise protocols have been developed. One of these is Reduced-Exertion High-Intensity Interval Training (REHIT), which comprises two repeated 20-s ‘all-out’ sprints with in a 10-minute protocol. Health benefits from REHIT have been demonstrated; e.g. REHIT improves V̇O2max and insulin sensitivity in healthy individuals. However, no studies have examined whether the REHIT protocol can be modified to make it either shorter or easier, without affecting the beneficial changes in V̇O2max. The effects of REHIT on V̇O2max in different participants still require investigation, and the mechanisms of the increase in V̇O2max remain unclear. Therefore, the aims of this thesis were to optimise the REHIT protocol to be a time-efficient and effective protocol for improved V̇O2max, to investigate the mechanisms underlying the improvement in V̇O2max after REHIT, and to examine the effect of REHIT on V̇O2max in type 2 diabetes (T2D) patients. Reducing the number of sprint repetitions (Chapter 2) and sprint duration (Chapter 3) attenuated the improvements in V̇O2max with REHIT, but training fewer sessions per week (Chapter 4) did not attenuate the improvements in V̇O2max. Importantly, the affective responses associated with REHIT are similar when compared with current exercise recommendations (Chapter 5). V̇O2max increases but insulin sensitivity does not change following REHIT in T2D patients (Chapter 6). Despite glycogen depletion using a protocol with single sprints, no changes in serum levels of the myokine SPARC nor V̇O2max were observed, so no information on possible mechanisms could be drawn from this thesis. Overall, it can be concluded that a manageable, effective and time-efficient exercise protocol for improving V̇O2max is REHIT, consisting of two 20-s ‘all-out’ cycle sprints within a 10-minute session performed at least two times per week