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Magnuson, Justine

University of British Columbia

The overall aim of my dissertation was to assess cortical and neuromuscular responses to both mental and physical fatigue. My first two studies showed that mental fatigue, induced by either a prolonged cognitively demanding task or sleep deprivation, resulted in slowed ongoing neural activity, less efficient evoked cortical responses, and worse accuracy on a complex reaching task. Study #1 also showed that after acute mental fatigue is induced, motor task performance recovers by ~40 minutes post-task, whereas slowed ongoing cortical activity and increased ratings of fatigue are still present until at least 60 minutes post-task, suggesting a different time course of recovery for behavioural and cortical responses. Study #2 showed that, in addition to slowed and impaired inhibitory control with sleep deprivation, task performance during an emotional inhibitory control task was even worse, suggesting interference of emotion processing on response inhibition. Study #3 assessed how two types of fatiguing submaximal contractions (matched-torque vs. matched-electromyographic activity, EMG) affected voluntary activation (VA), corticomuscular and intermuscular coherence, and motor unit discharge rates. I found higher coherence, worse VA, and increased motor unit discharge rates in response to the matched-torque task; however, during the matched-EMG task, when motoneuron pool output was maintained, VA and coherence scores were unchanged and motor unit discharge rates decreased. This suggests different compensatory strategies to maintain task performance during a matched-torque vs. matched-EMG fatiguing protocol. Lastly, given the limited understanding of antagonist motor unit behaviour, study #4 aimed to examine the recruitment patterns of motor units when acting as an agonist vs. antagonist. Surprisingly, I found no antagonist motor unit recruitment in most participants during ramped isometric contractions to MVC, despite appreciable surface-EMG activity. This study showed that motor units first recruited during an agonist contraction were seldom among those first recruited during an antagonist contraction. Overall, this dissertation provides important new insight into the cortical and motor responses to both mental and physical fatigue, and advances our understanding of motor unit behaviour.

Text

2023-01-25

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83752

Kinesiology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/