Optimising Exercise Intensity Prescription to Reduce Adaptive Variability Following High-Intensity Interval Training

The aim of this thesis was to optimise intensity prescription for high-intensity interval training (HIIT), ultimately enhancing the magnitude of the training stimulus, and reducing inter-individual variability in adaptive responses. In Chapter 4, it was demonstrated that %Δ, a method wherein maximal and submaximal performance determinants are considered to prescribe exercise intensity, elicits large inter- and intra-individual variability in performance, physiological, and perceptual responses to HIIT. In Chapter 5, the large interindividual variability observed in Chapter 4 was reproduced when %Δ and other methods of intensity prescription were tested, including percentage of maximal oxygen uptake, percentage of maximal work rate in an incremental test (%Ẇmax), percentage of average work rate sustained in a 20-min time-trial, and percentage expenditure of work capacity above critical power. In Chapter 6, it was demonstrated that prescribing HIIT with work intervals of variable power output may maximise the cardiorespiratory stress of training without incurring additional effort (quantified by ratings of perceived exertion) or metabolic stress (quantified by blood lactate concentration). In Chapter 7, it was demonstrated that most training sessions are completed by participants training at their maximal sustainable work rate, whereas sessions performed at 80%Ẇmax are often interrupted prematurely due to exhaustion, despite a similar training intensity on average. It was also demonstrated that the magnitude of inter-individual variability in adaptive responses, although only detected for maximal oxygen uptake and self-paced HIIT performance, was not influenced by how training intensity was prescribed. There were no prescription method effects on mean adaptive responses. Overall, this thesis questions some intensity prescription methods used for HIIT, provides evidence that varying power output during work intervals may maximise training stimulus, demonstrates that a maximal self-paced performance may be used as an intensity prescription benchmark, and challenges the belief that how training intensity is prescribed/normalised affects adaptive response variability