The effects of an in-flight perturbation on lower extremity biomechanics during drop landings
Yom, Jae Pom
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Most ACL injury-related researchers have focused increasingly on noncontact injury, because more than 70% of ACL injuries are categorized as such. However, this is a misleading classification because during movements involving a flight, then a landing phase, contact with another person or object (i.e., an unexpected perturbation) during the flight phase may set into motion a cascade of abnormal movements and mechanics that lead to an ACL injury during the subsequent landing phase. However, the possible mechanisms of such an ACL injury situation are not known. Therefore, the purpose of this study was to determine the effects of an in-flight perturbation on lower extremity biomechanics of females displayed during a drop landing. Seventeen collegiate-age-female recreational athletes performed baseline (BASE) then unexpected perturbation (PERT) or sham drop landings. For PERT trials, the cable attached to a proprietary perturbing machine pulled on one of the participant’s shoulders in a lateral direction during the flight phase. High-speed, digital-video motion and ground reaction force (GRF) data were recorded for the landing phase. We compared 95% confidence intervals of PERT – BASE differences scores (p<0.05) for lower-extremity joint kinematics and kinetics and GRF, using one sample t-tests. The results demonstrated that PERT, compared to BASE, exhibited more extended joint positions of the lower extremity at initial contact and greater knee abduction and hip adduction displacements. Additionally, PERT showed greater peak magnitudes of vertical and medial GRF, and knee and ankle extensor moments compared to BASE. Greater knee and hip adductor moments also were exhibited during PERT. We found that unexpected lateral in-flight perturbation leads to abnormal motions and GRF, but induces compensatory frontal plane moments that are beneficial for maintaining stability of the lower extremity from the lateral in-flight perturbation.