Structural and Organizational Strategies of Locomotor Modules during Landing in Patients with Chronic Ankle Instability

Abstract

Background: Human locomotion involves the coordinated activation of a finite set of modules, known as muscle synergy, which represent the motor control strategy of the central nervous system. However, most prior studies have focused on isolated muscle activation, overlooking the modular organization of motor behavior. Therefore, to enhance comprehension of muscle coordination dynamics during multi-joint movements in chronic ankle instability (CAI), exploring muscle synergies during landing in CAI patients is imperative.

Methods: A total of 22 patients with unilateral CAI and 22 healthy participants were recruited for this research. We employed a recursive model for second-order differential equations to process electromyographic (EMG) data after filtering preprocessing, generating the muscle activation matrix, which was subsequently inputted into the non-negative matrix factorization model for extraction of the muscle synergy. Muscle synergies were classified utilizing the K-means clustering algorithm and Pearson correlation coefficients. Statistical parameter mapping (SPM) was employed for temporal modular parameter analyses.

Results: Four muscle synergies were identified in both the CAI and healthy groups. In Synergy 1, only the gluteus maximus showed significantly higher relative weight in CAI compared to healthy controls (p = 0.0035). Synergy 2 showed significantly higher relative weights for the vastus lateralis in the healthy group compared to CAI (p = 0.018), while in Synergy 4, CAI demonstrated significantly higher relative weights of the vastus lateralis compared to healthy controls (p = 0.030). Furthermore, in Synergy 2, the CAI group exhibited higher weights of the tibialis anterior compared to the healthy group (p = 0.042).

Conclusions: The study suggested that patients with CAI exhibit a comparable modular organizational framework to the healthy group. Investigation of amplitude adjustments within the synergy spatial module shed light on the adaptive strategies employed by the tibialis anterior and gluteus maximus muscles to optimize control strategies during landing in patients with CAI. Variances in the muscle-specific weights of the vastus lateralis across movement modules reveal novel biomechanical adaptations in CAI, offering valuable insights for refining rehabilitation protocols.

Keywords: K-means clustering; chronic ankle instability; muscle activation model; muscle synergy; non-negative matrix factorization.

Figure 1

Overview of the overall workflow of the current study. (A) Acquisition of sEMG. (B) sEMG from 10 muscles were utilized to derive muscle activation using a muscle activation model. (C) Muscle synergy extraction using the NNMF algorithm. (D) Sorting of muscle synergies using the K-means clustering algorithm and Pearson’s correlation coefficient.

Figure 2

Muscle activation profiles during landing in the CAI and healthy groups following muscle activation model processing.

Figure 3

The extracted synergy vectors matrix and activation coefficient matrix from one to six subjects in the CAI group are presented, with activation coefficient results displayed in rows 1 and the remaining rows depicting the synergy vectors.

Figure 4

The extracted synergy vectors matrix and activation coefficient matrix from seven to 12 subjects in the CAI group are presented, with activation coefficient results displayed in rows 1 and the remaining rows depicting the synergy vectors.

Figure 5

The extracted synergy vectors matrix and activation coefficient matrix from one to six subjects in the healthy group are presented, with activation coefficient results displayed in rows 1 and the remaining rows depicting the synergy vectors.

Figure 6

The extracted synergy vectors matrix and activation coefficient matrix from seven to 12 subjects in the healthy group are presented, with activation coefficient results displayed in rows 1 and the remaining rows depicting the synergy vectors.

Figure 7

Global and local muscle VAFs. (A) The global VAF corresponding to each synergy in the CAI group. (B) The global VAF corresponding to each synergy in the healthy group. (C) The local muscle VAF corresponding to each synergy in the CAI group. (D) The local muscle VAF corresponding to each synergy in the healthy group. (E) Comparison of global VAF corresponding to muscle synergies 1–6 in the CAI and healthy groups.

Figure 8

Visualizations of K-means clustering results for all synergy vectors in the healthy group.

Figure 9

Correlation coefficients between synergy vectors and reference synergies for the 20 subjects in the CAI group. W: synergy vectors. RS: Reference Synergy.

Figure 10

Correlation coefficients between synergy vectors and reference synergies for the 20 subjects in the healthy group. W: synergy vectors. RS: Reference Synergy.

Figure 11

Visualization of four different movement modules corresponding to each of the four identified muscle synergies.

Figure 12

The synergy vectors, activation coefficients, and SPM1d results for activation coefficients in the muscle synergies extracted from each group. *: significant difference with p < 0.05.