Distinct Motor Modules After Anterior Cruciate Ligament Reconstruction During Stair Descent: A One-Year Longitudinal Study

Anterior cruciate ligament (ACL) injury often leads to lasting deficits in joint stability and neuromuscular control, even after reconstruction. Understanding how these deficits manifest during functional tasks is essential for improving rehabilitation strategies. This study recruited 25 male participants who had undergone ACL reconstruction, with assessments conducted at 3, 6, 9, and 12 months postoperatively. Surface electromyography (sEMG) signals from ten lower-limb muscles were collected during a standardized stair-descent task, and non-negative matrix factorization (NNMF) was applied to extract the corresponding muscle synergy patterns. Paired-samples t-tests and Wilcoxon rank-sum tests were performed to evaluate differences in muscle synergies between the ACL-reconstructed and contralateral limbs. Motor modules analysis revealed a preserved four-synergy structure in both limbs, with VAF exceeding 90%. At 3-6 months postoperatively, the reconstructed limb exhibited significantly elevated activation of the medial gastrocnemius (MG), biceps femoris (BF), and rectus femoris (RF) (p