Impaired Coordination and Recruitment of Muscle Agonists, But Not Abnormal Synergies or Co-contraction, Have a Significant Effect on Motor Impairments After Stroke.

Movement synergies, muscle co-contraction, and decreased motor drive to muscle agonists were suggested to be major factors in motor impairments after stroke. The purpose of this study was to investigate the major muscle mechanisms contributing to motor impairment after stroke. Twelve healthy and 13 post-stroke patients participated in this observational study. Both groups participated in a single experimental session, performing hand pointing movements in multiple directions, during which EMG was assessed. Additionally, the patients underwent the Fugl-Meyer assessment. A set of features from the electromyography (EMG) signal and co-contraction ratios were used to compare the capacity to modulate the muscle activity between the two groups of participants. A correlation analysis was applied between the Euclidian distances of each target and the Fugl-Meyer scoring assessment in the post-stroke patients. We found that impaired modulation of muscle activity in post-stroke patients was characterized by significantly increased Euclidian distances between the EMG features of different target directions and by a higher variability between muscle activation compared to healthy subjects. Impaired capacity to modulate muscle activity significantly correlated with the impairment status. In conclusion, impaired motor performance post-stroke systematic disturbance in the control signal to limb muscles, which manifests as decreased capacity to modulate muscle activity, rather than co-contraction of muscle antagonists or stereotyped movement patterns.