Neuromuscular Intervention Targeted to Mechanisms of ACL Load in Female Athletes

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 body's 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) and/or 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.

1. Specific Aim 1 Determine the mechanisms by which trunk motion increases knee load in females.

   Rationale Aim 1 Knee external abduction moment (LOAD) and lateral trunk motion (LTM) are known to be strong predictors of ACL injury risk in female athletes, but it is not known whether these predictors are linked and which athletes are at increased risk. In addition, we do not know the specific neuromuscular mechanisms that predispose these athletes to greater risk of injury. Neuromuscular control of the trunk will be examined relative to GRF position and magnitude, hip torque and knee LOAD. We will determine if increased ΔGRFv and increased relative hip adductor torque (HAdT) underlie increased knee LOAD in females.

   Central Hypothesis Aim 1 Lateral trunk motion will increase knee LOAD in female athletes by increased ΔGRFv, increased HAdT or by a combination of these two mechanisms during cutting and landing.

   Hypothesis 1.1. Increased LTM induced by unanticipated lateral cutting will increase knee LOAD by increasing ΔGRFv, adjusting for HAdT, in female athletes.

   Hypothesis 1.2. Increased LTM induced by single-leg medial drop landing will increase knee LOAD by increasing HAdT, adjusting for ΔGRFv, in female athletes.

   Hypothesis 1.3. Increased LTM induced by combined drop landing and unanticipated lateral cutting will result in combinatorial increases in knee LOAD by increasing ΔGRFv and HAdT in female athletes.

   Hypothesis 1.4 Females with low ΔGRFv, low HAdT, and low knee LOAD will form a distinct group or cluster of subjects, those with high ΔGRFv or HAdT and moderate LOAD will form another cluster, and those with high ΔGRFv, high HAdT and high LOAD will form the last distinct group using data collected during DLUC.

2. Specific Aim 2 Determine if NMT that decreases coronal plane trunk motion will decrease knee abduction LOAD in a double-blind cluster (by school and team) randomized controlled trial (RCT).

Rationale Aim 2 This aim will determine how NMT targeted to LTM and its two knee loading mechanisms, ΔGRFv and HAdT, will affect knee LOAD in low, moderate and high LOAD subgroups of female athletes.

Central Hypotheses Aim 2 NMT will increase control of coronal plane trunk motion and decrease knee LOAD by either mechanical (ΔGRFv), neuromuscular (HAdT) or both mechanisms and pre-test low, moderate and high knee LOAD subgroups of female athletes will demonstrate differential effects of NMT.

Hypothesis 2.1 Knee LOAD will be lower in trained than untrained females during landing and cutting.

Hypothesis 2.2 Post-test knee LOAD will not differ in trained high, moderate and low knee LOAD subgroups. Hypothesis 2.3 Post-test ΔGRFv and HAdT will not differ in trained high, moderate and low LOAD subgroups.

Hypothesis 2.3 Post-test knee LOAD, ΔGRFv and HAdT values will not differ from pre-test values in untrained high, moderate and low knee LOAD subgroups.

• Other: Neuromuscular Training
  Combination of exercises and phases to initiate lateral trunk perturbations that force the athlete to decelerate and control the trunk in order to successfully perform the techniques.
• Other: Speed Protocol
  Combination of exercises and phases to develop speed

• Experimental: Neuromuscular Training
  Combination of exercises and phases designed to initiate lateral trunk perturbations that force the athlete to decelerate and control the trunk in order to successfully perform the techniques.
  Intervention: Other: Neuromuscular Training
• Sham Comparator: Speed Training
  Speed training protocol
  Intervention: Other: Speed Protocol

Inclusion Criteria:

• Female
• Soccer, Basketball, or Volleyball athlete
• Attends Middle School or High School in Boone County or Fayette County KY

Exclusion Criteria:

• Male