Whole body mechanics of running turn maneuvers: Relationship to injury and performance

Anterior cruciate ligament (ACL) injuries are serious knee joint injuries that often occur during cutting, or running turn maneuvers. These maneuvers are frequently performed in multidirectional sports and are required for successful participation. Numerous studies have analyzed cutting movements in order to identify the mechanics related to potentially injurious knee joint loading and inform injury prevention training programs. However, the mechanics necessary to perform these turns has not yet been systematically characterized. It is not known how ACL injury prevention recommendations aimed at improving limb mechanics relate to the demands of cutting tasks. The specific aims of this dissertation were developed in order to better understand the whole body postural and joint/segmental strategies used by skilled individuals to perform running turn maneuvers and identify their relationships to performance and knee mechanics related to injury risk.;The purpose of Chapter III was to investigate the influence of cut angle on whole body postural adjustments prior to and during the cut's execution. To do this, whole body measures of center of mass velocity and position were compared across three tasks with varied deceleration and translation demands (straight running, and 45 and 90 degree sidestep cuts performed as fast as possible) in twenty-five healthy athletes. Ground reaction forces and impulse, and center of mass position relative to center of pressure were assessed in the anterior-posterior and medial-lateral directions during the approach and execution steps using separate two-way repeated measures ANOVA. When compared to straight running, cutting required greater deceleration and translation. Disproportionately greater braking but proportionately greater translation was observed with increased cut angle. The adjustments made in the approach step indicated that deceleration was prioritized over translation for the 90 degree cut but individuals distributed these demands more evenly during the 45 degree condition.;The purpose of Chapter IV was to investigate the influence of cut angle on joint and segmental mechanics. Twenty-five healthy athletes completed 45 and 90 degree cuts as fast as possible. Sagittal plane hip, knee, and ankle kinematics and kinetics were evaluated to determine the deceleration mechanics. Frontal plane hip and trunk and transverse plane hip kinematics and kinetics were assessed to determine redirection mechanics. A two-way multi-variate analysis of covariance (MANCOVA) determined that differences existed between task directions when considering all dependent variables and covarying for approach velocity (&agr; ≤0.05). Post-hoc analyses were then examined with paired t-tests. Systematic increases in joint and segmental variables were not found with increased cut angle. In particular, the role of the hip differed between tasks. It worked to stabilize the body in the sagittal and frontal planes during the 90 degree cut but propel and translate the body during the 45 degree cut.;The purpose of Chapter V was to identify and quantify the whole body postural and/or joint/segmental variables that were related to performance of cutting tasks, and to determine whether these variables also related to potentially injurious knee loading. To do this, correlation analysis was run between the completion time of the 45 and 90 degree cutting tasks (analyzed separately) and the dependent variables of interest. The correlated variables were then analyzed with two regression models, with completion time and peak knee adductor moment as the independent variables. During the 45 degree cut, sagittal plane hip mechanics were the strongest predictors of performance and were not predictive of knee loading. Only separation of the center of mass from the center of pressure in the medial-lateral direction during the 45 degree cut predicted both performance and knee loading, but it was a relatively weak predictor for both. During the 90 degree cut, primarily frontal plane mechanics predicted performance but did not predict knee loading. In general, the results indicated that different mechanics predicted performance for the two cutting tasks, and few variables were predictive of both performance and knee loading.;Taken together, the results of this dissertation indicate that individuals use different whole body postural and joint/segmental mechanics to accomplish cutting tasks performed to different angles. Accordingly, the mechanics predictive of cut performance and knee joint loading differed between cutting tasks. In particular, when individuals performed 45 and 90 degree cuts at their own maximal velocity, deceleration and translation demands differed and were accomplished with differences in whole body postural adjustments during and prior to the cut, and in joint/segmental mechanics. Furthermore, mechanics that were important to performance and knee joint loading differed between the cutting tasks. Results from this dissertation provide essential insight into quick change of direction tasks and have important implications for training programs aimed at reducing ACL injury risk.