Factors influencing corticospinal excitability during arm cycling

Lockyer, Evan J (2024) Factors influencing corticospinal excitability during arm cycling. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Humans can effortlessly navigate their environments and perform a variety of motor tasks, yet the neural processes underlying these movements are complex. The corticospinal pathway, a major descending pathway involved in the voluntary control of human movement, can be assessed non-invasively using various stimulation techniques. However, despite continued advancements in neurophysiology, our understanding of the corticospinal pathway’s role in dynamic, functional movements remains limited. This is partly because most research has focused on corticospinal excitability during static or minimally demanding tasks, leaving a substantial gap in our knowledge of its role during more natural, rhythmic motor outputs. In our lab, we use arm cycling, which resembles other forms of locomotion, to study the modulation of corticospinal pathway excitability under different conditions. This dissertation aims to advance our understanding of the neural control of arm cycling in healthy participants, specifically examining some of the factors that influence descending corticospinal drive and spinal motoneurone excitability during arm cycling. Chapter 2 presents an invited review paper outlining methodological considerations for studying corticospinal excitability during dynamic locomotor outputs, providing a foundation for the subsequent experiments. Chapters 3 to 5 contain studies published in peer-reviewed journals, each addressing specific research questions. In Chapter 3, we investigated whether focusing on maintaining a specified cadence during arm cycling would affect corticospinal excitability and found no significant effect. Chapter 4, explored how varying cycling and stimulation intensities would influence corticospinal and spinal excitability, revealing that both increased with cycling intensity up to a plateau, with differences observed by stimulation intensity. At high cycling intensities, we suggested that greater contributions from supraspinal centres may occur to produce the motor output. Chapter 5 examined the effects of a two-week arm cycling sprint interval training intervention on corticospinal and spinal excitability during arm cycling. The results showed enhanced spinal excitability post-training, with no change in corticospinal excitability. Given that no changes occurred in controls, we suggested that the increase in spinal excitability post-training represented a neural adaptation to training. Collectively, these findings enhance our understanding of the corticospinal pathway’s role during locomotor outputs and highlight the need for future work.

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