Biomechanical Changes in the Lower Limb After a Quadriceps Fatigue Task in Association With Dynamic Knee Valgus

Dynamic knee valgus (DKV), characterized by knee abduction and external rotation, has been associated with anterior cruciate ligament (ACL) injury, but the predictive accuracy of DKV for ACL injury remains unclear.

This controlled laboratory study examined fatigue effects on lower limb biomechanics and electromyography (EMG) during jump landing in healthy men. Participants were categorized into induced (n=11) and non-induced (n=8) DKV groups based on changes in knee abduction moment after a fatigue task.

Compared to the non-induced DKV group, the induced group exhibited a significantly reduced hip flexion angle (p=0.030), lower vertical ground reaction force (p=0.040), and decreased quadriceps peak EMG amplitude (p=0.008), along with a significant increase in hip internal rotation moment (p=0.001). Receiver operating characteristic analysis revealed that hip internal rotation moment had the highest discriminative power for classifying DKV occurrence, with an area under the curve (AUC) of 0.994 (95% CI: 0.960-1.000), followed by hip adduction moment (AUC = 0.896) and quadriceps peak amplitude (AUC = 0.883).

Findings suggest that DKV occurrence after fatigue is associated with altered quadriceps activity and hip rotation mechanics. These insights may inform ACL injury prevention strategies.