After stroke, inappropriate muscle activity phasing during the locomotor cycle is a key contributor to locomotor impairment. Muscle phasing has been shown to vary between behaviors post-stroke, but the degree to which individuals can voluntarily modulate activity is unclear. This dissertation consists of a series of three studies that investigate voluntary flexibility of inappropriate muscle phasing, using fixed-speed motorized pedaling to study the vastus medialis (VM), a uniarticular knee muscle. In the first study, I developed a method to estimate relative muscle activity phase in individual cycles, and demonstrated that even in a consistent task, muscle activity phase in paretic VM varies more than in non-paretic. In the second study, I presented participants with visual feedback to modify relative timing of VM activity within the locomotor cycle, and found, surprisingly, that participants demonstrated no significant difference in level of muscle activity modulation when providing feedback for paretic or non-paretic VM. Similarly, I found no significant effect of bilateral versus unilateral pedaling, surprising given prior studies demonstrating more impaired phasing in bilateral pedaling. More surprisingly, participants with greater impairment demonstrated greater modulation of activity phase. In the third study, I compared two methods for presenting challenge in visual feedback, and asked participants to advance muscle activation rapidly or using a behaviorally-anchored gradual presentation. Participants demonstrated a similar degree of change in both conditions, and performance between the two was closely correlated, despite notable differences in target deactivation. In brief, the findings of these studies suggest that when the behavioral task is carefully constrained, individuals show voluntary muscle activity phase flexibility that is surprisingly comparable between the paretic and non-paretic legs. These findings have interesting implications for future rehabilitation efforts, and open a range of further questions about the origins of inappropriate muscle activity phasing post-stroke.

Creator

• Mullens, Christopher Howard

DOI

• https://doi.org/10.21985/n2-f521-gc24

Subject

• Neurosciences

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:14729
• etdadmin_upload_672305

Date created

• 2019-01-01

Resource type

• Dissertation

Rights statement

• In Copyright