Article

OBJECTIVE: To investigate the timing and magnitude of muscle activation during an
active-assist bilateral hip motor task in human spinal cord injury (SCI). DESIGN:
A single test session using a novel robotic system to alternately flex and extend
the hips from 40 degrees of hip flexion to 10 degrees of hip extension at 1 of 3
frequencies (.25, .50, .75Hz). Subjects were asked either to actively assist the
movements or to remain relaxed during the imposed oscillations. SETTING: All data
were collected in a research laboratory. PARTICIPANTS: Ten subjects with motor
incomplete (American Spinal Injury Association grade C or D) SCI and 10
individuals without neurologic injury participated in this study. INTERVENTIONS:
Not applicable. MAIN OUTCOME MEASURES: Electromyograms and joint torques were
recorded from the lower extremities of SCI subjects and compared with
electromyograms and joint torque patterns recorded from 10 neurologically healthy
individuals completing the same tasks. RESULTS: In trials involving active
assistance of the imposed hip oscillations, SCI subjects produced muscle
activation patterns that were phased differently from muscle activity of
neurologically intact subjects. SCI subjects generated peak torque at the end
ranges of movement (ie, 40 degrees hip flexion, 10 degrees extension), whereas
control subjects generated the greatest torque midway through the movements.
Moreover, the phasing of active-assist hip torque in SCI subjects was similar to
the phasing of reflexive hip torques produced during the unassisted condition
(ie, SCI subjects instructed to relax), while control subjects produced no
reflexive torques during unassisted trials. CONCLUSIONS: The differences in the
timing of muscle activity during the active-assist task in controls and SCI
subjects highlights problems in generating appropriately timed muscle activity
during ongoing movements. The similarity in muscle activity patterns for the
active-assist and unassisted trials in SCI subjects further suggests that reflex
feedback from hip afferents contributes substantially to muscle activation during
active-assist movements. These findings demonstrate the disruptions in reflex
regulation of movement in people with incomplete SCI and suggest that spastic
reflexes might disrupt motor control.

Langue : ANGLAIS