Date of Award

Fall 2006

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Biomedical Engineering

First Advisor

Schmit, Brian

Second Advisor

Johnson, Michelle

Third Advisor

Hunter, Sandra

Abstract

The current study provides insight into the neural interaction between hip proprioceptive feedback and electrical stimulation of distal nerves of the leg. Functional Electrical Stimulation (FES) of paralyzed muscles in people with spinal cord injury has been used to restore lost muscle strength. However the same type of stimulation can result in reflex activation of muscles that could disrupt control of movement. Hip afferents and plantar cutaneous mechanoreceptors can also trigger reflex activity that modulates locomotion. Activation of these afferent pathways using FES can be used to provide feedback to spinal locomotor networks. The flexion reflex response to electrical stimulation was tested in all 20 subjects using two protocols. In the first 10 subjects the flexion reflex response to tibial nerve stimulation was measured in two hip postures and when stimulation was applied during imposed hip flexion and hip extension movements. In the second protocol (second set of 10 subjects), three stimulus sites, tibial nerve, common peroneal nerve and plantar skin, were tested at 2 static hip postures. Electrical stimuli were applied at 35Hz, for 1.43s at approximately 50% of motor recruitment to identify the effects of relatively long-lasting, moderate intensity stimuli. Sagittal-plane joint torques of the hip, knee and ankle were measured along with the electromyograms (EMGs) of 7 muscles of the legs in order to characterize the reflex response. The magnitude and habituation of the reflex response were measured for all test conditions. Hip torque and tibialis anterior EMO used as a metric of the flexion response showed a significantly higher response in the hip extension posture (- l 0°) as compared to the hip flexion posture (40°). Also, the hip flexion response habituated faster than the hip extension response across all the subjects. A similar trend in the data was observed with imposed hip movement, where the stimulation during hip extension was comparable to the static hip extended posture and stimulation during hip flexion to the static hip flexed posture. The reflex activation of the hamstrings however did not follow the flexion reflex pattern. The hamstrings response was higher in the flexed posture as compared to the extended and the overall response did not consistently show habituation in all the subjects. The results of this study indicate that hip position can play a key role in modulation of the flexion reflexes. Also, the non habituating response of the hamstrings for similar stimulation and position parameters could indicate the presence of an alternative reflex pathway which could be used to aid in knee flex ion during locomotion after spinal cord injury. Hence, the possibility exists that tapping into the hamstrings reflex pathway through hip proprioceptive afferents may be useful for improving knee flex ion during gait in people with spinal cord injury.

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