Abstract
BACKGROUND/OBJECTIVES: In order to guide and improve rehabilitation interventions for grip function after spinal cord injury (SCI), it is important to have a detailed understanding of the motor control strategies that the central nervous system uses to control the hand. We examined whether changes in the motor control of the hand after SCI are manifested in the form of changes to muscle synergies. We further sought to determine a correlation between functional ability and the extent of muscle synergy disruption. METHODS: Surface electromyographic (EMG) data were recorded from 8 hand muscles in 10 able-bodied subjects and 6 subjects with SCI as they performed various functional tasks using grip types relevant to activities of daily living. Muscle synergies were extracted using non-negative matrix factorization. Functional performance in each task was quantified using a 5-point clinical scale. RESULTS: The synergies most commonly observed in able-bodied subjects were co-activation of extensor digitorum communis and extensor indicis proprius, as well as of flexor digitorum superficialis with flexor carpi ulnaris. The proportion of subjects in which particular synergies occurred was significantly different for subjects with SCI compared to able-bodied subjects (P < 0.001). Deviations from the average able-bodied synergies in subject with SCI were found to be poorly correlated (r = -0.04) with functional ability. CONCLUSIONS: Results suggest that the disruptions and re-organizations of neural circuitry after SCI are reflected by the extracted muscle synergies, but the question of how muscle synergies can guide rehabilitation interventions remains open.