Abstract
Stroke survivors often experience motor impairments that include abnormal intermuscular coordination, which negatively affects individualized joint control. This lack of individualization is one of the fundamental motor control problems that largely explain voluntary movement impairment after stroke. Over the last decade, the concept of muscle synergy, here defined as a consistent ratio of muscle co-activation across muscles necessary to perform motor tasks, has been effectively applied to characterize intermuscular coordination following stroke. Developing non-invasive neurorehabilitation strategies to improve altered muscle synergy holds promise for advancing rehabilitative therapies; however, it remained largely unexplored. Here, we hypothesize that stroke survivors can improve the individualized activation of synergistic muscle coordination to decrease motor impairment through human-machine interaction guided by customized muscle synergies. In this study, three chronic post-stroke participants went through six weeks of a synergy-guided exercise that focused on independent control of each synergy identified from the major arm muscle activation. This study revealed three main findings: 1) chronic post-stroke participants could improve independent activation of synergistic muscle groups in the arm; 2) it was possible to modulate abnormal intermuscular coordination to resemble the intermuscular coordination patterns found in age-matched individuals; and 3) improving intermuscular coordination patterns showed the potential for reducing motor impairment. These results suggest that our novel synergy-guided exercise through human-machine interaction can improve stroke-induced neuromuscular coordination to reduce motor impairment.