In this blog, I am going speak about the myths of knee cave when squatting and provide an answer as to why it actually happens. This is for education purposes only – please consult a clinician or physiotherapist to have your injury assessed first!

This is known as knee valgus, which is commonly seen when people squat. Knee valgus is when the knee moves inwards, in relation to your hip and foot. This usually occurs through a combination of hip adduction and internal rotation with tibial external rotation. 

Why does this happen during a squat?

When performing a squat, you are often told to make sure that your knees stay in-line with your toes – having your hip, knee and foot in an almost straight line otherwise people will say that you have improper technique. However, when we squat this is not always the case.

Now unfortunately there are some very common mis-beliefs that knee valgus occurs because of glute muscle weakness or tight groin muscles but from research we know that it is not entirely true.

Bell et al in 2008 looked at the relationship between muscle strength and squat technique, and found that the individuals who had knee valgus with squatting also had greater strength in the hip muscles. Similarly, studies from Thijs in 2007 and Norcross in 2009 looked at the lunge and lateral step down movements, and found that hip strength was not associated with the amount of knee valgus demonstrated during these movements.

With relation to tight groin muscles, there is no research to date that has found any relationship to support this. From a biomechanical standpoint, it is does not make much sense because if the adductor muscles were tight then the knees would not be able to achieve the inline position because of a restriction/inflexibility.

So why does it happen then?

Knee valgus during a squat usually happens because of inefficient adductor recruitment and reduced knee flexion moment arm. In a lot of cases that we see this, it will be more noticeable during the deeper ranges of a squat.

There has been research completed by Vigotskyin in 2015 and Kubo in 2019, which both showed that the adductor muscles are very much involved with deep squats. As such, it makes sense that when you squat low down and begin to stand back up, the adductors will cause some degree of hip adduction along with extending the hip. Therefore, the heavier the load or more fatigue we elicit then the more muscles we need to recruit, especially the adductors and if we cannot recruit as much as we need to, this could lead to excessive knee valgus.

Another possible reason for knee valgus is a change in the knee flexion moment arm. How much demand is placed on a muscle is dependent upon the load and the distance the load is from the axis, also known as the moment arm. As the knee travels a further distance forward, the relative demand on the quads will increase. As you come up out of the `hole`, if the knees rotate inwards, this reduces the knee flexion moment arm, which reduces the demand on the quads. Once you pass the `sticking point` where the demand begins to reduce, the knees will then naturally rotate back out as the quads have less work to do.

It is more than likely that when people perform a loaded squat you will see a certain degree of knee valgus, especially when their effort level or load increases. To summarise, knee valgus is normal and is likely to happen when you squat down past 90 degrees of knee flexion on the way back up. It is thought to be because of muscles doing their job to get you back up from the `hole`. 

Is there an injury risk if you squat with your knees in?

Short answer is no. People are mistaken if they think that knee valgus could predispose them to an injury. Knee valgus has been wrongly associated with knee injuries. Due to this relationship, people are often told to avoid knee valgus during squatting movements with the fear of causing an injury. A squat has a very low risk, especially when you compare that to contact sports. Usually the knee will struggle with tendon related issues from an unbalanced load management or sprains due to a trauma.

What should you do about it?

If knee valgus is limiting your performance, then it may be worth addressing it, otherwise nothing. The first thing that people do when they try to address this issue is use a band around the knees.

While this is common, research has found this to be ineffective and even have the reverse affect. This is because if people use a band that is too strong for them then it could pull their knees into further knee valgus. Studies from Goovers et al, Foley et al and Reece et al. used loads of 40% of 1-rep-max up to 3-rep-max, all found that when using a band around the knees and squatting down, there was either no difference or an increase in knee valgus. Despite this, there are studies that have found a reduction in knee valgus with a banded squat, but these were with light resistance bands and no load.

Stance adjustment

Han et al in 2013 completed a study examining alterations in knee motion with three different squat stances – feet pointing forward, narrow with feet rotated in and a wide stance with feet rotated out. The narrower stance with feet rotated in resulted in more knee valgus, whereas the wide stance with rotated out shown the least knee valgus. From this, experimenting with your stance, particularly rotating your feet and standing wider, could reduce or increase knee valgus depending on which stance you choose.

Thank you for reading this. Please contact us with any questions that you may have or give us your feedback with your thoughts.