Fourfold Faster Knee Valgus Development During Single-Leg Landing Compared with Countermovement Jump: A Novel Approach to ACL Injury Risk Assessment

Dynamic knee valgus (DKV) is commonly used in functional screening related to anterior cruciate ligament (ACL) injury risk; however, assessments often rely on peak valgus alone despite the combined influence of knee valgus and flexion on knee loading. This study compared knee kinematics and vertical ground reaction forces (GRFs) between single-leg landing (SLL) and single-leg countermovement jump (SL-CMJ), focusing on peak knee valgus, knee flexion at peak valgus, valgus angular velocity, knee flexion-normalized valgus, and GRFs. Physically active, asymptomatic female participants (n = 30) performed both the SLL and SL-CMJ tasks. Knee kinematics and GRFs were recorded using motion-tracking sensors and a force platform. Peak knee valgus did not differ between tasks. Compared with SL-CMJ, SLL produced 24% less knee flexion at peak valgus, 17% greater knee flexion-normalized valgus, 254% higher valgus angular velocity, and 124% higher GRFs (all p < 0.05). These findings demonstrate task-dependent differences in landing mechanics that are not captured by peak knee valgus alone. Assessing knee valgus together with knee flexion and its temporal development may provide a more comprehensive characterization of potentially relevant knee-loading mechanics. The high valgus angular velocities observed during SLL may also inform the development of velocity-specific neuromuscular training strategies.