Background: In this study, we attempted to verify the hypothesis that further improvements in volitional movement of patients with a spinal cord injury would diminish and ultimately suppress the segmental responses, while enhancing the supraspinal inhibitory influence.
Methods: Eleven patients with an incomplete spinal cord injury and partial preservation of motor function (ASIS grades C and D) were recruited. Their lower limbs were evaluated using polyelectromyography (PEMG) during voluntary movements, reinforcement maneuvers, tonic vibratory reflex, passive stretch reflex, irradiation of the passive stretch reflex (PSRirrad), and plantar reflex suppression.
Results: The reinforcement maneuver response, tonic vibratory response, passive stretch reflex, and PSRirrad were most active in limbs with partially preserved volitional movement, but for which patients were still incapable of lifting their heel off the examination table. In contrast, plantar reflex suppression was strongest in limbs with partially preserved volitional movement, for which patients were capable of lifting the heel off the examination table.
Conclusions: Supraspinal inhibitory effects were most active in those limbs which were capable of lifting the heel off the examination table, compared to limbs with partially preserved volitional activity but without visible movement or which were incapable of lifting the heel off the examination table. The capability for volitional activity paralleled the supraspinal inhibitory effects.