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Influence of prior high intensity cycling at graded hypoxia on subsequent performance, neuromuscular and perceptual responses

Soo, Ding-Shun Jacky (2020) Influence of prior high intensity cycling at graded hypoxia on subsequent performance, neuromuscular and perceptual responses. Masters by Research thesis, Murdoch University.

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Muscle fatigue is characterised by a transient (reversible with sufficient rest) decline in force generating capacity of the active musculature. This deterioration in force production capacity is associated with impaired neuromuscular function integrity, which includes both central and peripheral factors. An oxygen-deprived environment (hypoxia) accelerates and/or exacerbates development of muscle fatigue and ultimately hampers exercise tolerance. However, it is unclear how hypoxia of different severity during an initial exercise bout may influence recovery and performance of a subsequent exercise bout. The overarching aim of this thesis was to assess the impact of graded hypoxia during an initial intermittent exercise bout, on subsequent performance and neuromuscular and perceptual responses during closed-loop (i.e., pre-determined number of repeated cycling sprints; Study 1) and open-loop (i.e., exhaustive intermittent cycling bouts; Study 2) tasks. Results from Study 1 (Chapter 3) showed that single sprint performance was restored during the subsequent set of repeated sprints despite substantial impairments in muscle contractility (~45% decrease in quadriceps potentiated peak twitch from baseline). The restoration of sprint performance during the subsequent sprint set coincided with the recovery in exercise-related sensations and quadriceps muscle activation, which suggests that the central nervous system plays an important role in the recovery of sprint performance. However, the relatively brief repeated sprint (with a known endpoint) may have consciously or subconsciously influenced participants’ pacing strategy to “overcome” the impaired neuromuscular function for short duration, and increase power output. Therefore, Study 2 (Chapter 4) investigated the effects of graded hypoxia during an exhaustive intermittent cycling bout on subsequent performance and associated neuromuscular fatigue characteristics. It was observed that the number of efforts performed during the second bout was substantially lower compared to the first bout at sea-level, despite 30 min of passive recovery. This suggests that the residual effect of fatigue may only become apparent when 2 exercise is performed until exhaustion during an “open-loop” exercise task. Increasing hypoxia severity reduced the number of efforts completed during the initial cycling bout, but did not influence performance or neuromuscular fatigue characteristics during the second bout. The effects of prior high intensity intermittent exercise at graded hypoxia on subsequent performance and neuromuscular fatigue characteristics were essentially minimal. The residual effect of fatigue was task dependent. Specifically, when the subsequent exercise is brief, compensatory process associated with central factors (e.g. perceptual recovery) may aid in sustaining exercise performance. However, where exercise is prolonged, for instance till exhaustion, performance decrements associated with residual fatigue becomes evident. An important and consistent finding across studies was that using the fraction of inspired oxygen as a marker of “hypoxic dose” elicited large inter-individual differences in response to hypoxia, and consequently performance. As such, Chapter 5 proposed an individualised approach to implementing hypoxia, using SpO2 to FiO2 ratio as a marker of dose. Collectively, our findings showed that neuromuscular fatigue during high intensity intermittent exercise in hypoxia and normoxia were largely peripheral in nature. However, prior high intensity exercise in graded hypoxia does not influence performance and associated neuromuscular functions during subsequent exercise.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation(s): Psychology, Counselling, Exercise Science and Chiropractic
Murdoch Applied Sports Science Laboratory
United Nations SDGs: Goal 3: Good Health and Well-Being
Supervisor(s): Girard, Oliver, Fairchild, Timothy, Ihsan, Mohammed and Scott, Brendan
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