Kinematic and Muscle Activity Differences During Change of Direction in Female Second Division Football Players Following ACL Reconstruction Compared with Uninjured Controls

The high rate of reinjury after anterior cruciate ligament reconstruction (ACLR), persistent sex-related disparity, and increased susceptibility during transitional stages in female football players highlight the need for more specific strategies to identify biomechanical parameters associated with valgus collapse. This study aimed to compare three-dimensional knee kinematic and synchronized electromyography (EMG) muscle activity of the medial and lateral thigh muscle complexes during a change of direction (COD) task, between ACLR and healthy controls players. A cross-sectional case–control study was conducted with 26 under-23 semiprofessional female football players (22.89 ± 2.68 years), divided into ACLR (n = 13) and control (n = 13) groups. The maximum and minimum peaks and range of knee angular velocity across three planes, along with the average and peak electromyography (EMG) muscle activity of the Biceps Femoris (BF), Semitendinosus (ST), Vastus Medialis (VM), and Vastus Lateralis (VL), were recorded during the preparation and load phases. Between-group differences were assessed using independent t-tests or Mann–Whitney U tests. Statistical significance after Holm–Bonferroni correction was established at p-Holm < 0.05. ACLR players demonstrated significant increased knee valgus angular velocity, alongside 4% reduced average ST muscle activity and 27% diminished peak BF muscle activity during the load phase, compared to controls. These findings indicate altered knee kinematic and muscle activity patterns during COD in ACLR players, suggesting persistent long-term functional adaptations in female football players after ACLR.