Performing low-intensity continuous exercise with blood flow restriction (BFR) results in increased maximal aerobic capacity (VO2max). The physiological adaptations responsible for this increase in VO2max are unknown. Four studies are presented within this thesis, with the main aim of examining known determinants of VO2max before and after training (blood oxygen carrying capacity, cardiac output, leg blood flow, oxygen extraction) to determine what physiological changes occur. Given that VO2max is tightly linked to endurance performance, another aim of this thesis is to examine whether BFR training can increase time trial performance in elite level athletes. In Study 1 we examined the effect of different cuff inflation pressures on the acute cardiovascular response to BFR exercise and measured blood volume regulating hormones after an acute exercise session. Observations from Study 1 suggested that BFR exercise causes a large release of blood volume regulating hormones, and with increasing cuff pressure there is an increased cardiovascular response. This led to the initial hypothesis that BFR training increased VO2max via increases in blood volume, which was refuted by blood volume measurements before and after training in Studies 2-4. Results from Study 3 suggest BFR training does not increase maximal cardiac output or the ability to extract oxygen but may increase maximal leg blood flow. Finally, conducting BFR training with national rowing team athletes provided evidence for improved time trial performance (lasting 6-7minutes), but improvements were not predicted by increases in VO2max or workloads eliciting specific blood lactate concentrations. Future research should confirm whether increases in leg blood flow after BFR training during whole-body exercise are responsible for increases in VO2max, and if so, then design future BFR protocols with the intention of manipulating factors known to increase arterial diameter or vasodilation. BFR training interventions examining exercise performance are scarce, suggesting more work studying whether applied performance outcomes improve are warranted before practical recommendations can be made.
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