Lower extremity muscle contributions to ACL loading during a stop-jump task.

Landing is considered a high-risk movement, especially landings from a stop-jump task, as they are often associated with lower extremity injuries, such as anterior cruciate ligament injuries (ACL). Females demonstrate lower extremity landing mechanics that often place them at a larger risk of injury compared to their male counterparts. While efforts have been made to understand lower extremity mechanics during stop-jump landings, little is known regarding the musculature function during these tasks and how they may influence ACL loading. Understanding lower extremity muscle contributions to ACL loading (F) may give insight to improving injury prevention protocols. Ten healthy, recreationally active females completed five trials of an unanticipated stop-jump task. Right leg kinematics, kinetics, and electromyography data were collected with three-dimensional motion capture, force plates, and electromyography sensors, respectively. Modified musculoskeletal models were scaled based on participant-specific anthropometrics, and muscle forces were obtained using static optimization. An induced acceleration analysis combined with a previously established mathematical ACL loading model was used to calculate lower extremity muscle contribution to F. The vastus lateralis, vastus intermedius, vastus medials, biceps femoris long head, semimembranosus, and soleus were found to be the primary contributors to F, with the vastus lateralis being the largest contributor. These data suggest that muscles traditionally known as ACL unloaders may in certain conditions load the ACL. These results also suggest that future injury prevention protocols should target muscles specifically to mitigate the influence the vastus lateralis has on ACL loading.