Knee valgus collapse refers to the inward movement of the knee during squatting motions or jump landings. Increased knee valgus angle is commonly linked with anterior cruciate ligament (ACL) tears but it’s also considered a risk factor for patello-femoral pain syndrome, meniscal tears, IT band syndrome, and knee osteoarthritis.
The exact cause of knee valgus collapse is not known. One theory is that weak hip abductor muscles cause poor control of knee movement in the frontal plane. Some evidence suggests however that the problem arises not from the hip abductors, but from increased activity of the hip adductor muslces (inner thigh) and muscles on either side of the ankle.
Knee Valgus and Muscle Activity
A 2012 study in the Journal of Athletic Training looked at the muscle activation patterns of subjects performing an overhead squat. The researchers found that subjects showing increased knee valgus during the squat had more muscle activity around in ankle (gastrocnemius and anterior tibialis muscles) and also in the muscles of the inner thigh (adductors) than the group without medial knee displacement. Hip abductor muscle activity was the same in both groups.
The researchers repeated the squat test, except with a 2 inch heel lift in the form of a wooden block placed under the sujects’ heels. With the heel lift, the knee valgus group showed less knee valgus during the squat than without using the lift. There was also a decrease in muscle activity around the ankle in both groups when using a lift.
The authors concluded that:
Medial knee displacement during squatting tasks appears to be associated with increased hip adductor activation and increased co-activation of the gastrocnemius and tibialis anterior muscles.
Since knee valgus was corrected by using a heel lift, the authors speculated that ankle stiffness caused by activity of the lower leg muscles in the valgus group leads to medial collapse of the knee as compensation for a decrease in ankle range of motion.
The increased activity in the adductor muscles may also explain the valgus collapse. Even though hip abductor activity was similar in both groups, increased adductor activity could cause an imbalance leading to the inward movement of the leg.
Knee Valgus and Ankle Mobility
What I found most interesting in this study is that the knee valgus collapse went away when a heel lift was used. Olympic weight lifting shoes have a lifted heel that gives an athlete a couple of advantages. A heel lift does two things:
- Increases available ankle range of motion allowing you to get into a deeper squatting position
- Displaces the body’s center of mass forward making it easier to keep your torso upright
Lifting shoes allow weight lifters to keep good form under heavy loads. They are not meant to substitute for good form. Using a heel lift for squatting is not a useful long-term solution for bad squatting mechanics.
Looking at knee injuries associated with valgus collapse, many occur in sports like soccer and volleyball where having an raised heel would be a disadvantage.
Controlling Knee Movement with Squatting
Based on the results from the study discussed earlier, an athlete looking to reduce knee valgus collapse and improve their squatting form should focus on:
- Increasing ankle mobility
- Keeping an upright torso
Since knee valgus occurs during the squatting motion, the best approach to correct the problem is to work on joint mechanics during an actual squat. It might be helpful to start with the heels lifted. This can be done by placing a small weight plate or book under each heel or by standing with the heels on a two-by-four.
Once an athlete understands and starts to establish control over the way their knees move during the squat they can progress to squatting with the heels flat.
Squatting with the arms overhead or holding a broom handle over your head is a good way to make sure the torso is staying upright. Here is a video that goes through several drills to improve squat mobility:
Increasing hip abductor strength with isolation exercises can also be beneficial. The subjects showing knee valgus in the study had four times greater acitivty in their adductor than in their abductors. Building up the strength of the abductors (gluteus medius and minimus) could reduce this imbalance and possibly result in better control of the knee in the frontal plane.
Finally, here are some general mobility and flexibility drills that can be used to improve squatting mechanics and limit knee valgus:
For anyone looking for more details on the knee valgus study, a great review of that work can be found on the Strength and Conditioning Research site.