Advancing Lower-Limb Post-stroke Rehabilitation: Leveraging Muscle Synergies and Multichannel Functional Electrical Stimulations

Functional electrical stimulation of muscles (FES) during task performance is a promising intervention that may effectively restore post-stroke motor impairment. Here, we characterize the efficacy of multi-muscle FES for gait rehabilitation when the FES stimulus is personalized based on the altered muscle synergies of the stroke survivor. Chronic hemiparetic stroke survivors were assigned to the FES (N = 23) or sham (N = 10) group. Customized FES (5 sessions) was applied to 6–7 muscles of the affected leg during overground walking (>600 steps per session). Individualized FES stimuli were constructed as muscle activities re-composed from selected muscle synergies of age-matched healthy subjects. Synergy-based FES induced higher increases in the lower-limb Fugl-Meyer score than sham FES. Significant improvements in knee flexion and ankle dorsiflexion were also observed in the FES group. More importantly, the subjects’ synergies selected for design of the FES stimuli had higher similarity to healthy synergies after FES in the FES group. Our results indicate that synergy-based FES may lead to motor functional improvement by promoting the recruitment of closer-to-normal muscle synergies for gait, thereby resulting in more naturalistic gait after FES.