This post originally appeared on the Athletic Lab blog.
Over the last decade or so, Anterior Cruciate Ligament (ACL) tears have skyrocketed even with increased training programs. A reason for this is that a disproportional amount of ACL tears occur in female athletes, who have increased participation in sport since the passing of Title IX. But why do so many ACL tears occur to female athletes? There has been research for many variables including looking at Q angles, hormonal differences, whether the athlete is menstruating, and also muscular imbalances. In this article, I’m going to explore the role of frontal plane motion at the knee in preventing ACL injuries.
When it comes to ACL tears there, has been a significant correlation between excessive dynamic valgus forces and tears in elite female athletes (Hewett, 2005). This excessive abduction of the knee is considered to be a neuromuscular inefficiency as when they compared trained female and male athletes they found that there were different landing patterns between the genders. Joseph et al. found was that during a drop jump followed by an immediate vertical jump, the timing and organization of ankle eversion, knee valgus, and hip adduction varied significantly between the two groups. In the women’s group, they found that they went through first knee valgus, then ankle eversion, and finally hip adduction whereas the men went through ankle eversion, knee valgus, and then hip adduction. This pattern, shown by the male group, is more optimal since we touch the ground with our feet first and the ground reaction forces are then transferred up the kinetic chain to the knees and hips. It should also be noted that in the women’s group, peak knee valgus and hip adduction occurred before peak knee flexion, or during the eccentric landing portion, and in the men’s group, knee valve and hip adduction occurred after peak knee flexion, or during the concentric power generating phase (Joseph et al, 2008).
While traditionally we may initially approach this problem by trying to coach the athlete to land with their knees out, or attempt to strengthen their lateral hip muscles to keep them from caving in; a different approach was taken in experimentation as it has been shown how dynamic valgus at the knee is accompanied with tibial internal rotation, and that “foot and knee motions are linked during weight bearing function.” Through this kinetic chain approach, Joseph et al. observed what happened when a medial post, an orthotic that is taller on the medial side and slants down towards the lateral side, was inserted into the athletes shoes during a drop jump and compared it to jumps without a post. They found significant decreases in knee valgus angles at both the peak and initial contact, as well as a reduction in the amount of ankle eversion and pronation which is also associated with ACL risk (2008). This is because the subtalar joint uses the frontal plane motion of the calcaneus to drive the tibia into internal rotation, which is accompanied by knee abduction. Through this limitation of eversion, the researchers were able to limit the amount of knee valgus seen during these tests.
What this signifies is that in these highly trained female athletes, changing the environment in the form of a medial post reduced the amount that the knee abducted while landing, which inherently reduced the risk of an ACL tear. While there may be muscular imbalances and deficits that also play a part to this risk, reeducating the neuromuscular system in female athletes to limit the amount of dynamic knee valgus can be extremely beneficial in creating more durable athletes, since controlling this deceleration is essential to almost all sports.
A simple way of adding this into a training plan is also quite simple, as all that is needed is two pieces of plywood and a 5kg plate set up in a way that the plate is on the floor with each piece of plywood laid partly on it so that it looks like a very wide and short pyramid (see above).
y performing bodyweight squats as part of the warm-up while standing on this structure, neuromuscular benefits in the form of less knee valgus will be seen, not only during the warm-up but also during working sets as this neuromuscular pathway has been primed to move in this pattern.
Hewett, T. E. (2005). Biomechanical Measures of Neuromuscular Control and Valgus Loading of the Knee Predict Anterior Cruciate Ligament Injury Risk in Female Athletes: A Prospective Study. American Journal of Sports Medicine, 33(4), 492-501. doi:10.1177/0363546504269591
Joseph, M., Tiberio, D., Baird, J. L., Trojian, T. H., Anderson, J. M., Kraemer, W. J., & Maresh, C. M. (2008). Knee Valgus during Drop Jumps in National Collegiate Athletic Association Division I Female Athletes. The American Journal of Sports Medicine, 36(2), 285-289. doi:10.1177/0363546507308362
Joseph, M. F., Rahl, M., Sheehan, J., Macdougall, B., Horn, E., Denegar, C. R., . . . Kraemer, W. J. (2011). Timing of Lower Extremity Frontal Plane Motion Differs Between Female and Male Athletes During a Landing Task. The American Journal of Sports Medicine, 39(7), 1517-1521. doi:10.1177/0363546510397175