Effect of Anticipation on Lower Extremity Biomechanics During Drop Jumps and Chop-Cutting Tasks

Abstract

INTRODUCTION: Sudden changes in direction or speed during sport-specific tasks like cutting and landing increase the risk of noncontact ACL injuries. The risk of injury during these tasks increases during unanticipated real-world scenarios where individuals are needed to react to external stimuli. Unanticipated tasks have been known to produce greater knee abduction and internal rotation angles as well as the associated joint moments. These variables are associated with increased ACL loading and therefore considered poor biomechanical adaptations to unanticipated tasks. Typically, anticipatory postural adjustments (APAs) of the trunk are used to accommodate movement. This study used a novel chopping approach to the cutting movement (also known as “quick feet”) to isolate the effect of anticipation on the lower extremities. The second novelty of this study was its ability to directly compare two unanticipated tasks associated with ACL injury. PURPOSE: Determine how knee biomechanics are affected by the anticipatory condition during drop jumps and chop-cut tasks. The primary hypothesis for this study was that unanticipated conditions during both tasks would produce biomechanical adaptations associated with increased ACL loading at initial contact (IC) and peak values calculated between 0-25% of ground contact. The secondary hypothesis of this study was that adaptations to the unanticipated conditions would be correlated between the left and straight directions of both tasks. METHODS: Motion capture data was collected on 22 recreationally active participants. During the drop jump tasks, the two directions analyzed were left leaning and straight (vertical). For the second task, participants performed a chop-cut at 60-degrees or a chop-straight run. The approach required participants to chop their feet for a minimum of 3 seconds before the cut or run. Unanticipated Conditions: Unanticipated conditions were created using FITLIGHT Training pods affixed to tripods in front of the participant. Just prior to ground contact for both tasks, one of the FITLIGHT pods illuminated, indicating the direction (either left/cut or straight). RESULTS: For the chop-cut and chop-straight tasks, significant condition*direction interaction effects were found for time to peak vGRF (p = 0.006), knee flexion angle at IC (p = 0.011), and knee internal rotation angle at IC (p < 0.001). For the drop jump tasks, significant main effects for condition were found for knee flexion angle at IC (p = 0.026) and peak knee adduction moment (p = 0.021). Significant Pearson correlation coefficients were found for the change scores between conditions during the chop-cuts and left drop jumps for knee abduction and internal rotation angles at IC and peak. CONCLUSION: Unanticipated conditions produced some knee biomechanics associated with increased ACL loading, but it was direction specific. The lack of condition main effects suggests the use of anticipatory postural adjustments to protect the knee from injury. Furthermore, kinematic adaptations to the unanticipated conditions were correlated between tasks which indicate that the adaptations are not task specific. These findings emphasize the importance of using multiple tasks and conditions during injury risk assessment and doing so on an individual basis.