Biomechanical effects of different change of direction angles on lower limb joint load and injury risk in soccer players

This study investigated the biomechanical effects of different change of direction (COD) angles (45°, 90°, 135°, and 180°) on lower limb joint loads and injury risk in 26 male soccer players. Using three-dimensional motion capture, force platforms, and electromyography, we analyzed joint kinetics, kinematics, and muscle activation patterns during standardized COD tasks. Data were analyzed using repeated-measures ANOVA with Bonferroni post-hoc corrections (α = 0.05), with effect sizes reported as partial eta-squared (ηp²). Results demonstrated progressive increases in peak knee abduction moment (141% from 45° to 180°) and dynamic valgus index (152% increase), with a critical nonlinear threshold at 90°. Sharper CODs (≥ 135°) produced high-risk biomechanical patterns, with 88% of participants exceeding ACL injury risk thresholds during 180° tasks compared to 19% at 45°. Earlier hamstring activation (12.3% vs. 18.7% of stance phase) and increased muscle coactivation were observed at sharper angles. These findings suggest soccer training programs should prioritize angle-specific injury prevention for CODs ≥ 135°, including progressive eccentric strengthening, neuromuscular control training, and technique modification targeting reduced knee abduction moments and enhanced dynamic stability.