Prelanding Knee Kinematics and Landing Kinetics During Single-Leg and Double-Leg Landings in Male and Female Recreational Athletes.

Biomechanical behavior prior to landing likely contributes to anterior cruciate ligament (ACL) injuries during jump-landing tasks. This study examined prelanding knee kinematics and landing ground reaction forces (GRFs) during single-leg and double-leg landings in males and females. Participants performed landings with the dominant leg or both legs while kinematic and GRF data were collected. Single-leg landings demonstrated less time between prelanding minimal knee flexion and initial ground contact, decreased prelanding and early-landing knee flexion angles and velocities, and increased peak vertical and posterior GRFs compared with double-leg landings. Increased prelanding knee flexion velocities and knee flexion excursion correlated with decreased peak posterior GRFs during both double-leg and single-leg landings. No significant differences were observed between males and females. Prelanding knee kinematics may contribute to the increased risk of ACL injuries in single-leg landings compared with double-leg landings. Future studies are encouraged to incorporate prelanding knee mechanics to understand ACL injury mechanisms and predict future ACL injury risks. Studies of the feasibility of increasing prelanding knee flexion are needed to understand the potential role of prelanding kinematics in decreasing ACL injury risk.

Indirect contact matters: Mid-flight external trunk perturbation increased unilateral anterior cruciate ligament loading variables during jump-landings.

PURPOSE: To determine the effect of unanticipated mid-flight medial-lateral external perturbation of the upper or lower trunk on anterior cruciate ligament (ACL) loading variables during jump-landings. METHODS: Thirty-two participants performed double-leg vertical jump-landings while bilateral kinematics and kinetics were collected under 6 conditions (upper or lower trunk perturbation locations; no, left, or right perturbation directions). Two customized catapult apparatuses were created to apply pushing perturbation to participants near the maximal jump height. RESULTS: The ball contacted participants near the center of mass for the lower-trunk conditions and approximately 23 cm above the center of mass for the upper-trunk conditions. Under upper-trunk perturbation, the contralateral leg demonstrated significantly smaller knee flexion angles at initial contact and greater peak knee abduction angles, peak vertical ground reaction forces, peak knee extension moments, and peak knee adduction moments compared to other legs among all conditions. Under lower-trunk perturbation, the contralateral leg showed significantly smaller knee flexion angles at initial contact and increased peak vertical ground reaction forces and peak knee extension moments compared to legs in the no-perturbation conditions. CONCLUSION: Mid-flight external trunk pushing perturbation increased ACL loading variables for the leg contralateral to the perturbation. The upper-trunk perturbation resulted in greater changes in ACL loading variables compared to the lower-trunk perturbation, likely due to trunk and ipsilateral leg rotation and more laterally located center of mass relative to the contralateral leg. These findings may help us understand the mechanisms of indirect-contact ACL injuries and develop jump-landing training strategies under mid-flight trunk perturbation to better prevent ACL injury.