Assessment of ankle muscle activation by muscle synergies in healthy and post-stroke gait

Abstract

Objective: Impaired ankle dorsal and plantar flexor function is a frequent sequela of stroke. A better assessment of ankle muscle activation would be highly significant for stroke rehabilitation. The challenge in implementing current electromyography (EMG)-based assessments is due to problems with the variability and individuality of ankle muscle EMG profiles during walking. We have been studying a new technique using the muscle synergy method to quantify the characteristics that underlie ankle muscle activation to address this issue. Approach: We processed surface EMG signals from ankle muscles and gait parameters collected from 20 healthy and 22 post-stroke subjects during walking. A non-negative matrix factorization algorithm was used to extract muscle synergies. Main results: Our results suggest a featured muscle synergy structure (R = 0.84, 95% CI: 0.83–0.85) underlying ankle muscle activation in both healthy and post-stroke subjects. The structure of the featured muscle synergy was robust in the same subjects across different conditions in the healthy group (R = 0.97, 95% CI: 0.96–0.98) and the post-stroke group (R = 0.95, 95% CI: 0.88–0.97). Compared to the stroke group, the synergy patterns of healthy subjects showed better regularity and higher inter-subject similarity (P = 0.001). In addition, the results of muscle synergies were indicative of locomotor performance. Significance: The innovative quantitative results of this study can help us to better understand ankle muscle activation and will be a reference for clinical assessments and intervention studies.