 Females who participate in cutting and landing sports suffer anterior cruciate ligament ACL injuries at a 2 to 10-fold greater rate than males participating in the same high-risk sports. Fifty to 100 percent of ACL injured females will suffer osteoarthritis of the injured knee within one to two decades of the injury. External knee abduction moment LOAD predicts ACL injury with high sensitivity and specificity in female athletes. Control of lateral trunk motion LTM also predicts ACL injury with similar levels of sensitivity and specificity in female athletes. These predictors may be linked, as lateral positioning of the trunk can create high knee abduction load via both biomechanical and neuromuscular mechanisms. The mechanism of ACL injury in females include high knee LOAD and high LTM, with the majority of body weight shifted over the injured limb and the foot positioned lateral to the bodys center of mass. An unanticipated perturbation is also often a contributor to the injury mechanism. LTM may result in increased knee LOAD by increasing the lateral position and magnitude of the GRF vector ΔGRFv or by increasing reactive hip adductor torque HAdT. Our long-term objectives are to determine the mechanisms that cause ACL injury in female athletes and to develop neuromuscular training NMT interventions that specifically target these mechanisms. If the objectives of this proposal are achieved, an evidence-based NMT intervention will be developed and made available nationally that will effectively and efficiently reduce ACL injury risk in high-risk female athletes. The major goal of this proposal is to determine if increased LTM increases coronal plane knee load in high-risk groups of female athletes. This application will test the central hypotheses that LTM increases knee LOAD and that NMT that is targeted toward increasing coronal plane control of trunk motion will decrease knee LOAD in females with moderate and high knee LOAD. Aim 1 is designed to determine the mechanisms by which trunk motion may increase knee LOAD in female athletes. Coronal plane control of the trunk LTM will be examined relative to ΔGRFv, HAdT and knee LOAD. We will determine if increased LTM increases knee LOAD by biomechanical increased ΔGRFv andor neuromuscular increased relative HAdT mechanisms that may underlie increased LOAD in female athletes. The central hypothesis of Aim 1 is that increased LTM will increase knee LOAD in female athletes by increasing ΔGRFv, by increasing HAdT or via a combination of these mechanisms during cutting and landing. We hypothesize that females with neither mechanism will have low knee LOAD, those with increased ΔGRFv or HAdT will have moderate LOAD and those with increased ΔGRFv and HAdT will have high knee LOAD. Aim 2 is designed to determine if NMT that decreases coronal plane trunk motion will decrease knee LOAD in knee load group clusters in a randomized controlled trial. The central hypothesis of Aim 2 is that NMT will decrease knee LOAD in the moderate LOAD group by decreasing ΔGRFv or HAdT and will decrease LOAD to the greatest extent in the high LOAD group by decreasing both ΔGRFv and HAdT. 