Characteristics of the locomotor-like muscle activity during orthotic gait in paraplegic persons.

We previously found that orthotic gait training can induce 'locomotor-like' coordinated muscle activity of the paralyzed lower limb in persons with spinal cord injury (SCI). The purpose of the present study was to characterize the locomotor-like muscle activity based on data obtained from electromyographic recordings and motion analysis during orthotic gait in nine motor complete SCI subjects. Seven of nine subjects showed a common EMG activation pattern mainly in the ankle (soleus: Sol) and hip extensor (biceps femoris: BF) muscles. The locomotor-like muscle activity was well synchronized with the gait cycle, namely, the EMG amplitude of both Sol and BF muscle had common temporal relationships with the ground reaction force, and hip and ankle joint motions. While the presence or absence of the EMG activity during orthotic gait was consistent with those of mechanically-induced stretch reflex, the duration and amount area of the locomotor-like muscle activity were significantly longer than those of the stretch reflex in the Sol muscle. Moreover, the Sol EMG magnitude had strong relevance to hip as well as ankle angular velocities. These results indicate that the locomotor-like muscle activity during orthotic gait is not a mere reflex response, but includes an activity of the central pattern generator (CPG) and its interaction with afferent inputs. Orthotic gait training for complete SCI persons might have a potential to activate the spinal locomotor center.