Differences in Kinematic and Muscle Activity between ACL Injury Risk and Healthy Players in Female Football: Influence of Change of Direction Amplitude. Cross-Sectional Case-Control Study

Abstract

Background and Objectives: Anterior cruciate ligament (ACL) injury rates remain high and have a significant impact on female football players. This study aims to evaluate knee kinematics and lower limb muscle activity in players at risk of ACL injury compared to healthy players during three side-cutting tests. It also investigates how the amplitude of change of direction influences stabilization parameters. Materials and Methods: A cross-sectional case-control study was conducted with 16 participants (23.93 ± 5.16 years), divided into Injured (n=8) and Healthy groups (n=8). Injured players had a history of non-contact knee injury involving valgus collapse, without undergoing surgical interven-tion. Three change of direction tests: Change of Direction and Acceleration Test (CODAT), Go Back Test (GOB), and Turn test (TURN) were used for evaluation. The peak and range of knee joint angles and angular velocities across three planes, along with the average rec-tified and peak envelope EMG signals of the Biceps Femoris (BF), Semitendinosus (ST), Vastus Medialis (VM), and Gastrocnemius Lateralis (GL), were recorded during the prep-aration and load phases. Group differences were analyzed using two-factor mixed-model ANOVA with pairwise comparisons. Statistical significance was set at p < 0.05. Results: Injured players demonstrated lower external tibial rotation angular velocity and a greater range of motion in tibial external rotation compared to Healthy players. Additionally, the Injured showed significantly higher average rectified muscle activity in VM and GL both increased by 4% during the load phase. The CODAT and TURN tests elicited higher Bf and VM muscle activity, compared to the GOB test. The TURN test also showed greater extension angular velocity in the sagittal plane. Conclusions: The results revealed differ-ences in knee kinematics and muscle activity between players at risk of ACL injury and healthy players, influenced by the amplitude of directional changes. Players altered transverse plane mechanics and increased VM and LG activation during LOAD may re-flect a dysfunctional motor pattern, while the greater sagittal plane angular velocity and VM and BF activation from CODAT and TURN highlight their higher potential to replicate ACL injury mechanisms compared to GOB. Clinical Implications: This study highlights the importance of assessing kinematics in conjunction with specific muscle activity during functional tests that replicate ACL injury mechanisms, in order to better determine player risk profiles and design more effective prevention programs.