Effects of exercise-induced fatigue and lunge direction on racket-side lower-limb biomechanics during forward lunges in male badminton athletes

Purpose This study examined the effects of exercise-induced fatigue and lunge direction on racket-side lower-limb biomechanics during forehand and backhand forward lunges in male badminton athletes. Methods Twenty-four male athletes performed standardized three-step lunges before and after a combined sprint-interval running and maximal vertical-jump fatigue protocol. Three-dimensional kinematics were recorded using a Vicon motion-capture system, while ground reaction forces were recorded using force platforms. Lower-limb biomechanical analyses focused on the racket-side limb. Outcome variables included phase durations, joint kinematics and moments, center-of-mass (COM) velocity, ground reaction forces (GRFs), impulses, joint quasi-stiffness, and dynamic postural stability. Outcomes were analyzed using two-way repeated-measures ANOVA with prespecified biomechanical-domain- and effect-specific Benjamini–Hochberg false discovery rate correction. Results No statistically significant fatigue × direction interactions were detected after BH correction; however, given the limited statistical sensitivity for interaction effects, these findings should be considered inconclusive. Fatigue shortened braking duration, reduced recovery-phase COM velocity gain, braking-phase impulses, recovery-phase anteroposterior impulse, and selected joint ROMs, while increasing recovery-phase hip and knee quasi-stiffness. Backhand lunges showed greater secondary-impact GRF, higher DPSI, VSI and MLSI values, greater ankle dorsiflexion and inversion, and a greater knee extension moment than forehand lunges. Conclusion Within the racket-side limb, fatigue induced a more constrained lunge strategy and reduced recovery-phase impulse generation and COM velocity increase. Backhand lunges showed greater impact loading, braking-phase force fluctuations, and ankle mechanical demands than forehand lunges.