Lower limb biomechanics and knee tissue loading under fatigue during the badminton forward lunge in recreational female players.

BACKGROUND: Badminton is widely promoted as a lifelong physical activity, yet repetitive forward lunges performed under fatigue may increase the risk of knee injury, particularly among recreational female players. Although fatigue-related changes in lower-limb biomechanics have been reported, their influence on tissue-level knee loading remains unclear. This study investigated the effects of fatigue on lower-limb biomechanics and internal knee loading during the badminton forehand forward lunge. METHODS: A within-subject repeated-measures experimental design was used. Sixteen recreational female badminton players performed standardized forehand forward lunges before and after a fatigue protocol. Three-dimensional lower limb kinematics and kinetics were collected using a motion capture system and force platform. Time-varying biomechanical differences across the stance phase were analyzed using one-dimensional Statistical Parametric Mapping. A subject-specific finite element model was developed to evaluate stress and strain in the patellofemoral cartilage, menisci, and anterior cruciate ligament under the peak vertical ground reaction force (vGRF) loading condition. RESULTS: Fatigue induced alterations in lower limb biomechanics throughout the stance phase (%), including reduced knee flexion (2.6-16.4%, p = 0.02, 54.8-65.7%, p = 0.03) and ankle dorsiflexion (0.0-36.2%, p < 0.01) with increased ankle eversion (69.0-93.3%, p < 0.01). At the peak vGRF instant, hip abduction decreased (p < 0.01), whereas knee varus angle (p = 0.02) and internal valgus moment increased (p = 0.04). Finite element analysis demonstrated greater loading of passive knee tissues after fatigue, with patellar cartilage contact pressure increasing by 16.4%, patellar cartilage von Mises stress by 19.3%, medial meniscal stress by 5.5%, and anterior cruciate ligament (ACL) stress and maximum principal strain by 7.4 and 18.4%, respectively. In addition, the regions of peak ACL stress and strain shifted toward the femoral attachment after fatigue. CONCLUSION: Fatigue altered lower limb biomechanics and increased passive knee tissues during the badminton forehand forward lunge in recreational female players, indicating a less favorable mechanical environment for the knee under fatigued condition. Recognition of these biomechanical changes may help reduce knee injury risk and support long-term badminton participation among recreational female players.