Date of Award

Spring 2006

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Biomedical Engineering

First Advisor

Schmit, Brian D.

Second Advisor

Knikou, Maria

Third Advisor

Hunter, Sandra

Abstract

Sensory feedback from hip proprioceptors has been demonstrated to markedly affect motor output in both animals and spinal cord injured SCI patients during walking and under static conditions. The aim of this study was to investigate the effects of sinusoidal hip movements on the soleus H-reflex in chronic motor incomplete SCI subjects when administered alone and following excitation of group I antagonistic muscle afferents. Soleus H-reflexes were recorded alone and during common peroneal nerve stimulation at either short (2, 3, and 4 ms) or long (80, 100, and 120 ms) conditioning test (C-T) intervals. In healthy subjects, the conditioning reflex effects at these intervals are associated with reciprocal Ia and presynaptic inhibition, respectively. The right hip joint was subjected to sinusoidal hip movements at 0.2 Hz while subjects were lying supine. Electromyographic (EMG) potentials of five leg muscles and sagittal-plane joint torques were recorded simultaneously. The soleus H-reflex was significantly depressed during hip flexion and was facilitated during hip extension (ANOVA, P<0.05), while prestimulus soleus EMG activity did not contribute significantly to the reflex modulation (t-test, p=O. 721 ). A phase-dependent modulation of actions from the antagonistic muscle afferents was present during hip movement, with reciprocal and presynaptic inhibition significantly reduced during hip extension and reinforced during hip flexion (ANOVA, P<0.05). Spastic EMG and reflexive joint torques were found to depend on the specific phase of the hip movement. This study provides evidence that in human SCI, imposed sinusoidal hip movements modulate soleus H-reflex in a similar manner to that observed during static hip angle changes, and that complex intemeuronal reflex circuits contribute to the reflex modulation. These intemeuronal circuits are likely to be important to motor functional recovery of SCI patients.

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