Regulation of power output during self-paced cycling exercise

Thomas, Kevin (2013) Regulation of power output during self-paced cycling exercise. Doctoral thesis, Northumbria University.

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Abstract

Fatigue is a universal phenomenon with functional and perceptual consequences. The study of fatigue in the exercise sciences has historically focussed on factors that limit performance during exercise. More recent proposals have shifted the focus of this understanding to examine how intensity is regulated during exercise through the study of the pacing strategy, which has both physiological and practical consequences. The aim of this thesis was to investigate the biological basis of self-pacing and the optimum pacing strategy for endurance time-trial events. Study 1 assessed the reproducibility of the pacing strategy and the consistency of the performance, perceptual and physiological response during self-paced time-trial exercise in well-trained cyclists. This study demonstrated the existence of a global pacing strategy that was reproducible on repeat 20 km cycling time-trials (TTs), and consistent between 4, 20 and 40 km TTs. The performance, perceptual and physiological response was also reproducible, confirming the feasibility of studying manipulations of the self-pacing strategy and the subsequent impact on these variables. Studies 2 and 3 adopted a model whereby participant’s best self-paced TT performance was used to set time- and work-matched exercise bouts to study the effect of even- and variable-pacing. These studies revealed that a variable-pacing strategy that contains frequent periods of high-intensity exercise resulted in an augmented physiological response and higher perception of exertion compared to time- and work-matched even- and self-paced exercise. Conversely, even-pacing resulted in attenuation in the metabolic and perceptual cost of the bout, but only when the self-selected pacing strategy was sub-optimal. When self-pacing was optimal, time- and work-matched even-pacing resulted in cumulative metabolic stress that caused early exercise termination. In study 4 the biological basis to fatigue during 4, 20 and 40 km TTs was assessed. This study demonstrated that the contribution of central and peripheral mechanisms of fatigue during self-paced exercise is task-dependent. Specifically, the shorter, higher intensity 4 km time-trials were characterised by a greater degree of peripheral fatigue and less central fatigue compared to longer, lower intensity 20 and 40 km time-trials where less peripheral and more central fatigue was observed. The supraspinal contribution to fatigue was alsomgreater during longer TT exercise. These studies have provided novel insight in to the biological factors that underpin the regulation of self-paced exercise, and the optimum pacing strategy for endurance TT events.

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