A Novel Lower-Limb Coordination Assessment Scheme Using Multi-Scale Nonlinear Coupling Characteristics With sEMG.

Motor dysfunction (e.g., incoordination of upper or lower limb) significantly limits the individuals' ability of daily living, and thus the provisioning of a motion coordination assessment method becomes of vital importance. As a quantitative indicator, intermuscular coupling strength could assess limb coordination. Since surface electromyography (sEMG) signals cover nonlinear coupling characteristics, in this article, a lower limb motion coordination assessment scheme with intermuscular coherence (IMC) analysis and optimization variational mode decomposition (VMD) is proposed. First, sEMG signals are decomposed into several intrinsic mode functions (IMFs) using optimized VMD. Then, the nonlinear coupling feature vector in the beta-band frequency domain (15-35 Hz) is extracted by the G-P algorithm from optimal IMF, thereby estimating the intermuscular coupling strength by IMC. In particular, differential evolution (DE) algorithm's global optimization capability and envelope entropy (EE)'s sparsity are adopted to provide the basis for optimization VMD and screening optimal IMF, respectively. Finally, signals are collected from four muscle pairs of the 12 male and 12 female subjects to assess lower limb motions' coordination. Simultaneously, the independent sample T test is leveraged to compare the effects of gender on groups' characteristics (e.g., age, height, and body mass). Results demonstrate not only the effectiveness of the proposed approach (i.e., p < 0.01 with both "S-walking" and "Running" motions, p < 0.05 with "Q-walking") but also the difference in motion coordination relationship between male and female adults as well as the significance of muscle selection.