Posterior Trunk Pulling Perturbation Increased Variables Associated With Anterior Cruciate Ligament Loading in Both Sagittal and Frontal Planes During Landing.

Trunk perturbation before initial ground contact (IC) is associated with increased anterior cruciate ligament (ACL) injury risk. The purpose of this study was to determine the effect of midflight anterior and posterior pulling perturbation applied to the upper trunk on ACL loading variables during landings. Participants performed double-leg vertical jumps with and without anterior or posterior pulling perturbation. The perturbation was created by a customized device, pulling participants through a freely dropping slam ball before IC. Whole-body kinematics and ground reaction forces were collected using optoreflective cameras and force plates. Data from 31 participants were included for analysis. The posterior pulling perturbation resulted in the significantly smallest peak trunk and knee flexion angles, the greatest peak knee abduction angle, and peak knee extension and adduction moments during landings. The anterior pulling perturbation resulted in the significantly greatest peak trunk flexion angle and smallest peak knee extension moment among all conditions, and significantly greater peak knee flexion angle, smaller peak knee abduction angle, and smaller peak knee adduction moment compared to the posterior pulling perturbation. The findings suggest increased ACL loading variables and potential injury risk associated with midflight posterior pulling perturbation and provide information for understanding indirect-contact ACL injury mechanisms.