Muscle synergies and functional network organization underlying Tai Chi movements: a pilot cross-Sectional study...

Tai Chi (TC) integrates coordinated upper-lower limb movements and bilateral motor patterns that enhance neuromuscular control. Despite its rehabilitation potential, patients with motor dysfunction often find standard TC postures difficult to perform, and target muscles vary across individuals. This study aimed to characterize muscle synergies and functional networks during TC to inform personalized rehabilitation. Twenty-three experienced practitioners performed the 24-form TC sequence while surface electromyography (sEMG) signals were recorded from 16 bilateral upper- and lower-limb muscles. Muscle synergies were extracted using non-negative matrix factorization (NNMF), with model order selected using variance accounted for (VAF). Normalized mutual information (NMI) quantified intermuscular connectivity, and graph-theoretical metrics - clustering coefficient (C), path length (L), modularity (Q), and small-worldness (σ = γ/λ) - characterized network organization and hub muscles. Two whole-body synergies were identified. They showed high repeatability across trials (cosine similarity = 0.9708 ± 0.0352) and high consistency across participants (0.9281 ± 0.049). In the 23-participant NMI subset, connections between opposite sides within the upper or lower limbs were stronger than connections on the same side (mean paired ΔNMI = 0.0332, 95% bootstrap CI [0.0322, 0.0342], Holm-adjusted p = 0.0059). In the descriptive ranking analysis, 88.3% of the five highest-NMI pairs in each movement connected opposite sides of the body. The functional networks showed small-world properties. Modularity ranged from 0.23 to 0.41, and 62.5% of movements had Q > 0.30. Movements with Q ≤ 0.30 were interpreted as having weaker community structure. Lower-limb muscles, especially the gastrocnemius and tibialis anterior, frequently acted as network hubs. This pilot study demonstrates that TC elicits stable bilateral muscle synergies and small-world network organization in experienced practitioners, indicating an underlying neuromotor framework for coordinated movement. Future studies should examine whether these synergy patterns can be adapted or retrained in patients with motor impairments, such as stroke survivors, using appropriate control groups.

www.chictr.org.cn, identifier ChiCTR2400080158.