Neuromuscular control strategies during the Tai Chi heel-kick movement across different levels of motor experience.

Objective: This study aimed to examine differences in neuromuscular control strategies during the Tai Chi heel-kick movement between practitioners with different levels of motor experience by integrating estimated spinal segmental motor output, muscle synergy analysis, antagonist muscle co-contraction, and joint coordination assessment. Methods: Sixteen male Tai Chi practitioners were divided into a Master-level group (n = 8) and a first-class group (n = 8) according to official Chinese athlete certification. Kinematic, kinetic, and surface electromyography data were synchronously collected using a Vicon motion capture system, Kistler force platform, and wireless surface electromyography system. Estimated spinal segmental motor output, muscle synergy number and structure, co-contraction index (CI), center of activity (CoA), full width at half maximum (FWHM), and joint coordination parameters based on continuous relative phase (CRP) were quantified. Results: Descriptive group-average profiles showed different temporal and rostrocaudal patterns of estimated lumbosacral motor output between groups. The participant-level mean number of muscle synergies did not differ significantly between the Master-level and first-class groups (3.73 ± 0.37 vs. 3.63 ± 0.33, p = 0.499). Three representative group-level synergy modules were identified in both groups, with module-specific differences in muscle-weighting composition. The CoA of matched M1 occurred significantly earlier in the Master-level group than in the first-class group (p = 0.004), whereas the CoA of M2 and M3 and the FWHM of all three modules did not differ significantly between groups. None of the four lower-limb co-contraction indices differed significantly between groups. Phase-level coordination analysis showed a more in-phase but more variable supporting-limb hip-knee pattern during push-off and a more in-phase and less variable kicking-limb hip-knee pattern during recovery in the Master-level group. Conclusion: Greater motor experience was associated with selective and phase-specific differences in neuromuscular organization rather than with a general reduction in synergy number or co-contraction. The findings were characterized primarily by module-specific activation timing and phase-dependent hip-knee coordination.