JERREL BUSHEL. The association between auditory external focus of attentional feedback and drop landing biomechanical risk factors of ACL injury. (Under the direction of ABBEY THOMAS FENWICK) Introduction: Poor lower limb biomechanics during drop landing can increase the risk of anterior cruciate ligament (ACL) injury. Landing with decreased hip and knee joint flexion and increased vertical ground reaction force (vGRF) may place greater strain on the ACL and result in serious injury. External focus of attention has proven to yield better functional performance in the lower extremities during drop landing compared to internal focus of attention. Moreover, the use of auditory biofeedback (AudFB) during an external attentional focus-based exercise intervention may be beneficial in producing biomechanical changes during drop landing tasks. Objective: To determine the association between AudFB and changes in biomechanical risk factors associated with ACL injury. Methods: Participants performed fifteen jump landing trials at baseline. Participants then completed 12 AudFB sessions over 4 weeks. During each session, participants completed 6 sets of 6 reps of each exercise on both limbs. New exercises were added throughout the progression of the program. Participants’ jump landing biomechanics were retested 1week after the intervention. Biomechanical data were processed using a standard inverse dynamics approach and submitted to statistical analysis. Errors committed during the exercises were tracked throughout the 4 weeks and totaled across each limb for every exercise. The association between number of errors committed and changes in jump landing biomechanics were determined via Pearson Product Moment correlation analysis. Results: There were significant associations between changes in left hip sagittal torque and total errors, total errors on the left leg, errors on DL landing, and total and left leg errors on the SL squat and SL step down. There was a significant association between change in right hip sagittal torque with the right leg errors on the SL step down. Change in left knee sagittal torque was associated with errors on right leg SL squat, while changes in right knee sagittal torque were associated with total errors, total errors on the right, errors on the right leg SL and DL drop landing, errors on the right leg SL step down, and the total and right leg errors on the SL squat. A change in right knee frontal torque was significantly associated with total errors on SL step down, and errors on DL drop landing. There was a change in left hip frontal rotation associated with errors on DL drop landing. A change in right knee sagittal rotation was significantly associated with errors on DL drop landing, and total and left leg errors on SL drop landing. Finally, there was a significant association between changes in left knee frontal rotation with total and right errors on SL drop landing. There were no significant associations between changes in vGRF with errors committed. Conclusions: While AudFB yielded changes in lower extremity biomechanics, the changes presented were primarily to sagittal plane biomechanics and, as such, may not be sufficient to reduce ACL injury risk. The practical use of an AudFB device with the aim of improving drop landing biomechanics and reducing the risk of ACL injury may be valuable but warrants refinement.