Decreased change of direction angle, increased ACL load: angle-dependent anterior cruciate ligament loading across different change of direction sprints in male soccer players

Anterior cruciate ligament (ACL) injuries frequently occur during high-speed, non-contact movements such as change of direction (COD) maneuvers. While external joint moments such as the knee abduction moment (KAM) are widely used as surrogate markers of ACL loading, they do not directly quantify tissue loading. Understanding ACL loading at tissue level and how it varies with COD angle may improve prevention and screening protocols. Fifteen recreational male soccer players performed planned 45°, 90°, 135°, and 180° COD sprints. Marker trajectories and ground reaction forces were captured with three-dimensional motion capture system and force plates. Musculoskeletal simulations were conducted in OpenSim using a multi-body knee model and the Concurrent Optimization of Muscle Activations and Kinematics framework. Knee kinematics and kinetics in all three anatomical planes, ACL strain and ACL strain rate were extracted across COD angle conditions. Repeated measures ANOVAs with post-hoc tests were applied. Peak ACL strain ranged from 5.1 to 8.5%, and ACL strain rate reached up to 84%·s⁻1. Both parameters were highest at 45° COD. These values fall within physiologically plausible ranges reported in in-vitro and in-vivo studies. ... mehrDespite higher KAMs for increased angles, ACL strain and ACL strain rate decreased with increasing COD angle. Musculoskeletal simulations revealed that smaller COD angles impose greater ACL loading in male soccer players, illustrating that surrogate metrics such as KAM may not accurately reflect ACL loading. These findings emphasize the multifactorial nature of ACL loading. It further demonstrates the value of musculoskeletal modelling as a comprehensive approach to quantify ligament loading and inform angle-specific injury-prevention and testing strategies.