Stroke-Induced Hemiplegia Alters Muscle Coordination Patterns During Standing: A Weighted Recurrence Network Analysis

Background: A given movement requires precise coordination of multiple muscles under the control of the central nervous system. However, detailed knowledge about the changing characteristics of neuromuscular control of multi-muscle coordination in stroke survivors during standing is still lacking. This study aimed to investigate the stroke-linked neuromuscular dysfunction of lower limbs during standing from the perspective of multi-muscle dynamical coordination patterns by utilizing a novel network approach — weighted recurrence network (WRN).

Methods: Ten male hemiplegic patients with first-ever stroke and 10 age-matched healthy adults were instructed to stand quietly for 30 s with eyes opened and eyes closed, respectively. The WRN was constructed based on the surface electromyography signals of 16 muscles from the trunk, hips, thighs, and calves. Relevant topological parameters, including clustering coefficient (C) and average shortest path length (L), were extracted. The degree centrality (DC) derived from the WRN was introduced to evaluate the effects of a single muscle on the dynamical coordination of multiple muscles. Relationships between muscular network parameters and standing-related assessment metrics including the level of standing balance and the area of COP were also analyzed.

Results: Results showed that the post-stroke hemiplegic patients stood with remarkably higher similarity of muscle activation and more coupled inter-muscular dynamics, characterized by higher C and lower L (p < 0.05) than the healthy subjects. The DC values and rankings of back, hip, and calf muscles on the affected side were significantly decreased, whereas those on the unaffected side were significantly increased in the hemiplegia group compared with the healthy group (p < 0.05). A decrease in C and an increase in L of WRN were observed with increased standing balance capacity and decreased COP areas (p < 0.05). Without visual feedback, subjects exhibited enhanced muscle coordination and increased muscle involvement (p < 0.05).

Conclusions: These findings revealed that stroke-induced hemiplegia could significantly influence neuromuscular control, which was manifested as higher similarity and strengthened coupling in muscle activation. These results suggested abnormal apraxia of muscles on the affected side, compensation of muscles on the unaffected side, and pronounced visual dependence due to stroke. This study provides a novel analytical tool for evaluation of neuromuscular dysfunction in stroke-induced hemiplegic patients, and could be potentially applied in clinical practice.