Analysis of muscle synergy for evaluation of task-specific performance in stroke patients

Muscle synergy represents a central neural module that organizes and activates a group of muscles when performing a certain task. However, whether muscle synergy is a good physiological indicator of motor ability in task performance for patients suffering stroke is not clear. The purpose of this study is to understand how information of task-specific muscle synergy in healthy subjects and patients post stroke can be used to evaluate their motor ability, and further to assist motor rehabilitation for stroke patients. Electromyography (EMG) signals and movement kinematics in reaching tasks were recorded in 5 healthy subjects and 4 stroke patients. Muscle synergies were extracted from EMGs and compared cross healthy and stroke subjects. Normal synergies displayed a characteristic pattern common in healthy subjects. But pathological synergies in stroke subjects lacked the characteristics of normal synergy without a common component, implicating varying extent of damage to the motor module due to lesion in cerebral circuits. Further analysis in stroke subjects showed that pathological patterns of synergy in stroke subjects corresponded to the abnormality in their movement control compared with healthy subjects. Data showed that task-specific muscle synergy did reveal a positive correlation to the ability of neural control of tasks. It was further observed that task-specific synergy was changed towards the normal pattern after intervention with functional electrical stimulation in patients post stroke.