Biomechanical asymmetry during side-cutting is associated with lower limb muscle strength after anterior cruciate ligament reconstruction

The relationship between muscle function recovery and biomechanical alterations after anterior cruciate ligament reconstruction (ACLR) during high-risk movements remains unclear. This study aimed to investigate lower-limb muscle strength across multiple angular velocities (concentric and eccentric contractions) and knee biomechanics during side-cutting at 9 months post-ACLR, and to explore their association. Thirty-six participants (21 males, 15 females) at 9 months post-ACLR completed three-dimensional motion analysis during side-cutting and isokinetic strength testing (concentric: 60, 180, 300°/s; eccentric: 60°/s). Paired t-tests analyzed interlimb differences; Spearman’s correlation assessed limb symmetry index (LSI) correlations. The reconstructed limb demonstrated reduced peak knee flexion angle (P < 0.001, Cohen’s d = 0.91), extension moment (P < 0.001, Cohen’s d = 1.05), and vertical ground reaction force (P = 0.011, Cohen’s d = 0.45), alongside increased external rotation angle (P = 0.035, Cohen’s d = 0.37). Concentric quadriceps strength was weaker at 60°/s (P = 0.010, Cohen’s d = 0.46), 180°/s (P = 0.001, Cohen’s d = 0.58) and 300°/s (P = 0.001, Cohen’s d = 0.62), concentric hamstring strength was also reduced at 300°/s (P = 0.037, Cohen’s d = 0.36). Knee flexion angles showed a strong positive correlation with concentric quadriceps strength at 180°/s (r = 0.512, P = 0.001), while external rotation angles correlated moderately negatively with both concentric quadriceps strength and concentric hamstring strength at 300°/s (r = -0.410, P = 0.013; r = །0.467, P = 0.004). At the vGRF peak, the extension moment correlated positively with eccentric quadriceps (r = 0.377, P = 0.023) and hamstring strength (r = 0.364, P = 0.029) at 60°/s. At nine months post ACLR, persistent interlimb asymmetries in side-cutting biomechanics and thigh muscle strength were observed, with moderate correlations between them, particularly at medium to high angular velocities. These findings suggest moving beyond maximal strength training in rehabilitation. Incorporating velocity-specific and eccentric training, together with isokinetic strength assessment at velocities such as 180°/s and 300°/s in return-to-sport criteria, may help reduce reinjury risk.