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 induce knee abduction load via both biomechanical and neuromuscular mechanisms. The mechanism of ACL injury in females most often includes high knee LOAD and high LTM, with the majority of body weight shifted over the injured limb and the foot positioned lateral to the body's center of mass. An unanticipated perturbation is also often a contributor to the injury mechanism. LTM may result in increased knee LOAD via lateral positioning and increased magnitude of the GRF vector ( GRFv) or by altered reactive hip adductor torque (HAdT). Our long-term objectives are to determine the mechanisms that increase ACL injury risk 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 alters LOAD in 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 LOAD in females. 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 GRFv, HAdT and knee LOAD. We will determine if increased LTM increases knee LOAD via biomechanical (increased GRFv) and/or neuromuscular (increased relative HAdT) mechanisms. The central hypothesis of Aim 1 is that increased LTM will increase knee LOAD in female athletes by increasing GRFv, 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 GRFv or HAdT will have moderate LOAD and those with increased GRFv and HAdT will have high knee LOAD. Aim 2 is designed to determine if NMT targeted to decreases coronal plane trunk motion (TNMT) will decrease both LTM and knee LOAD to a greater extent than sham/control training in a randomized controlled trial (RCT). The primary hypothesis of Aim 2 is that TNMT will decrease LTM and knee LOAD. Secondary hypotheses will test relationships between changes in LTM, GRFv, HAdT and LOAD with TNMT using Post-Hoc analysis. Neuromuscular Intervention Targeted to Mechanisms of ACL Load in Female Athletes. PUBLIC HEALTH RELEVANCE. Females who participate in cutting and landing sports like soccer and basketball suffer anterior cruciate ligament (ACL) injuries at a 2 to 10-fold greater rate than males participating in the same high-risk sports. Our previous work shows that lateral knee load and trunk motion can each independently increase ACL injury risk in female athletes. The major objectives of this proposal are to determine how lateral trunk motion increases knee load in female athletes who are at greater risk ACL injury and to develop exercise training programs that decrease trunk motion, knee load and ACL injury risk in these high-risk athletes.