The role of pacing in sub-maximal and maximal intensity exercise: impacts of environmental and protocol manipulations

The purpose of this thesis was to investigate the role of pacing in the development of fatigue through four studies which examined the impact of environmental and protocol manipulations, and evaluated the role of an ability to fluctuate pace during exercise at sub-maximal and maximal intensities. The role of self-pacing in exercise protocols represents a distinct contrast to the use of enforced-pace exercise common in many conventional scientific protocols, and thus required the development of novel methodologies, relevant to current sporting practices, which were shown to demonstrate validity and reliability using a range of contemporary measures. Chapters 1-3 of this thesis provided a rationale for the studies, a review of relevant literature, and an overview of the scientific methodologies common to the studies. The study in Chapter 4 reported the findings of an investigation comparing 1) selfpaced and 2) enforced-pace exercise at matched intensities. This study demonstrated that self-paced exercise poses a reduced metabolic challenge when compared to matched-intensity enforced-pace exercise. The study findings suggest that the ability to voluntarily fluctuate power output in accordance with transient sensations of fatigue may represent an important physiological mechanism used during self-paced exercise to defend homeostasis. The study in Chapter 5 reported the test-retest reliability of a self-paced perceptually regulated time-trial by comparing power output responses within- and between-groups of aerobically-matched participants. Using a range of reliability measures this study showed that all participants were able to reliably reproduce the same power output over 5000m at a fixed rate of perceived exertion (RPE 15) providing evidence of the reliability of a sub-maximal time-trial protocol based on a fixed RPE score both withingroups and between independently sampled groups. Chapter 6 reported a study which investigated the effects of intervals of radiant warming and thermoneutral conditions on pacing during a sub-maximal perceptually regulated exercise test. Participants completed 5000m rowing trials in 1) warmed, 2) non-warmed, or 3) interval-warmed conditions. Dynamic analysis of results showed a significant reduction in power during the first warming bout in the interval warmed condition, which was unobserved in the second period of warming. The ability to complete each exercise bout with similar average power and performance time, despite significant changes to pacing within the trial demonstrated evidence of a multi-level pacing plan with the capacity to alter effort during a bout in response to thermal challenges, but without impact to overall performance within a trial. The final study in Chapter 7 reported the design of a novel perceptually regulated test of maximal aerobic power. The study compared physiological and performance responses to repeated 1) self-paced perceptually regulated maximal exercise tests and 2) conventional incremental maximal exercise tests. Similar peak power outputs and VO2peak were observed in the self-paced and conventional, enforced pace exercise tests (p>0.05). The findings of this study validated a reliable self-paced maximal exercise test (VO2peak CV<1%; icc 0.999) that presents a protocol which can be applied across multiple modalities, furthermore the dynamic analysis of the performance responses in this novel protocol provided evidence of energy-sparing pacing behaviours unobservable using conventional measures. This thesis has shown the importance of self-pacing in exercise through outcomes which cannot be demonstrated when the pace of an exercise bout is externally enforced. The imposition of an enforced pace results in an increased physiological demand in response to a mode of performance that is unrelated to current sporting practices. The positive impact of self-pacing on performance and physiological variables demonstrated in this thesis suggests that the ability to vary pace, under the influence of a model of complex metabolic control, is fundamental to optimal performance, and the incorporation of self-paced protocols in exercise testing is vital to the continued development of models of fatigue.