Characterization of paraplegic disturbance response during FNS standing

The application of functional neuromuscular stimulation (FNS) to paralyzed muscle as a potential method of rehabilitation for paraplegic spinal cord injury and stroke patients is addressed. Feedback control of electrical stimulation to the muscles of the lower extremity, based on knee angle measurements, can be used to maintain stance in the presence of disturbances. This study considers the disturbance response of a paraplegic subject using a combination of open-loop stimulation of the hamstrings, gluteus maximus, and erector spinae and feedback-controlled stimulation of the quadriceps to maintain stance. The characterization of posture involved examination of two different components of postural control: the early automatic responses of the knee under closed-loop control and the later involuntary and voluntary responses of the subject´s upper body. Knee recovery was complete within approximately 600 ms after the onset of the disturbance. However, the subject exhibited postural responses which continued to right the upper body up to 1300 ms after the onset of the disturbance