Measuring changes to force control variability using Lyapunov exponents: looking at the influence of anterior cruciate ligament injury and reconstruction and high performance athletics

Buchanan, ThomasRupture of the anterior cruciate ligament is a common sports related injury that results in significant financial burden. A significant amount of research has been conducted to understand function and recovery after ACL tears. Of particular interest, is understanding biomechanics of running and cutting maneuvers as these tasks lead to a majority of ACL tears. Recently, the use of nonlinear analysis techniques have provided promising results in a number of biomechanical applications. Specific to ACL injury, researchers using maximal Lyapunov exponents found significant changes to kinematic control at the knee. However, nonlinear kinetic changes that may occur after ACL injury have yet to be explored. The goals of this dissertation were to explore the use of nonlinear techniques as they relate to the control of multidirectional ground reaction forces in recreational athletes (uninjured controls), high performance athletes, ACL deficient patients, and ACL reconstructed patients and to evaluate how nonlinear measures relate to both injury mechanism and task performance. As a part of this dissertation we developed a force control task that utilizes real time visual feedback of a person's force production to understand force control variability, as measured by maximal Lyapunov exponents. For the first two aims the force control task was used to study recreational athletes, high performance athletes, ACL deficient individuals, and ACL reconstructed individuals. The third aim was divided into two parts, one which explored force control variability and ACL injury mechanism, and one which evaluated the relationship between force control variability and task performance. For the first part of aim 3, ACL deficient subjects were divided by injury mechanism, contact versus noncontact and LyE values were assessed. For the final part of this aim, high performance athletes completed a series of sport-like tasks including a cutting maneuver, a lateral shuffle, and a deceleration task and biomechanical data from these tasks were then correlated with LyE data from the force control task. From this work we found that recreational and high performance athletes had similar mGRF control in their right and left limbs. Recreational athletes additionally generated similar LyE in both the anterior/posterior (AP) and medial/lateral (ML) directions, while high-performance athletes generated lower LyE values in the ML direction indicating superior mGRF control in that direction. In our exploration of force control variability after ACL injury and reconstruction, we found significantly larger force control variability in both ACL-d and ACL-r subjects when compared to healthy controls and high performance athletes. This deficit in mGRF control may be a significant contributor to ACL re-injury as it may affect the ability to perform different running and cutting tasks. Those who experience a contact injury exhibit mGRF control deficits through LyE measures which suggests that secondary tissue commonly seen in contact injuries correlate with average stance time in all sport-like tasks tested. As LyE values increased, which indicates poor control, average stance time decreased. Understanding not only how mGRF control changes after ACL injury and reconstruction, but the dynamic interplay between LyE and injury mechanism and LyE and sports performance, helps biomechanists get a more complete picture of force control variability. This work can assist in developing new rehabilitation techniques and training programs that can not only enhance performance but improve injury recovery. Nonlinear analysis techniques have the potential to be a powerful addition to our current clinical knowledge base.Ph.D.University of Delaware, Biomechanics and Movement Science Progra