Background: The 11+ program prevents anterior cruciate ligament (ACL) injuries in athletes through unknown mechanisms.
Purpose: The aim of the current study was to evaluate the effects of The 11+ intervention program, performed by female soccer players during a single season, on the frequency of Early Peaks during athletic tasks.
Methods: Three teams (69 players) of collegiate female soccer athletes (Divisions I and II) were recruited. Two teams (49 players) volunteered to perform The 11+ three times per week for one season (~22 weeks plus three weeks pre-season), and one team (20 players) served as controls. The athletes performed three repetitions of a cutting maneuver, side shuffle direction change, and forwards to backwards running direction change before and after the competitive season and were recorded using marker-based 3D motion capture. Knee valgus moment time series were calculated for each repetition with inverse kinematics and classified as either "Very Early Peak", "Early Peak" or "other" using cluster analysis. The classification was based timing of the peak relative to the timing of ACL injuries. The effect of the intervention on the frequency of Very Early Peaks and Early Peaks was evaluated with a mixed Poisson regression controlling for the movement task and pre-season frequency.
Results: The 11+ intervention reduced the frequency of Early Peak knee valgus moment in one intervention team (coefficient = -1.16, p = 0.004), but not the other (coefficient = -0.01, p = 0.977). No effect was observed on the frequency of Very Early Peak knee valgus moment.
Conclusions: Reduced frequency of knee valgus moment Early Peak during athletic tasks may explain the mechanism by which The 11+ program decreases risk of ACL injury. Prospective studies with a much larger sample size are required to establish a link between Early Peak knee valgus moments and risk of ACL injury.
Level of evidence: 2b.
Keywords: Cluster analysis; biomechanics; injury prevention; knee; soccer.