Date of Award
Spring 2011
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biomedical Engineering
First Advisor
Schmit, Brian D.
Second Advisor
Hyngstrom, Allison
Third Advisor
Buchanan, James T.
Abstract
Following a spinal cord injury (SCI), people often experience exaggerated reflexes, such that mild provocations can cause prolonged and uncontrolled muscle activity throughout the entire leg. These reflexes can be problematic and are known to interfere with functional tasks, such as transferring to and from a wheelchair, and they may interfere with locomotor function by prolonging muscle activity and/or inappropriately activating muscles during attempts to walk. While these multijoint reflexes have been shown to originate from several afferent cues, hip afferent input is a particularly potent sensory signal that readily triggers multijoint reflexes. The overall objective of this dissertation was to understand the role of hip sensory cues and the potential mechanisms associated with multijoint reflex behavior in human SCI. To evaluate this, a custom -built robot was used to impose movement of the legs about the hip joint. Joint torque and muscle activity were used as quantitative measures of reflex activity in SCI subjects. The findings from this suggest that the mutability of reflexes triggered by hip-mediated sensory signals is reduced. Voluntary effort and stretch-sensitive sensory feedback impart weak signals that do not significantly alter multijoint reflex patterns. Additionally, reflex behaviors presented with a distinct temporal response that has been associated with the disregulation of voltage-dependent depolarizing persistent inward currents (PICs). These results further elucidate the underlying mechanisms associated with hyperexcitable multijoint reflexes to help guide rehabilitation techniques for controlling unwanted muscle activity and for increasing functional gains in human SCI.