I have heard my patients question me about letting their knees go over their toes in the past but I seem to be hearing this question a lot lately. It seems that a lot of people have been taught to never let their knees go over their toes when doing squats, lunges or anything really. Not only is it OK to allow your knee to flex over your toes but this is very normal in natural human movement. Try walking down a hill or a flight of stairs without your knee going over your toes. This is impossible unless you turn and descend sideways.
Where did this idea come from? I assume it came from the fact that a lot of people experience pain in their knees when flexing the knee to a certain angle when doing squats, lunges or descending a flight of stairs and so trainers and doctors advised these people to avoid this pain at all costs including never letting the knee go over the toes. But avoiding a problem is not a very effective way to solve a problem.
But first things first. Let’s take a look at a full or deep squat.
Image credit to Phyeasyque.com
In the above image you can see that not allowing the knee to go over the toes results in a greater forward lean at the spine resulting in increased stress at the low back. The image claims an increased load on the low back of 1070%. I am not sure of the accuracy of that number but it is clear that there is more load on the muscles of the low back due to the forward position. You can also see that the hip is not at or below the height of the knee. If the hip were to drop to or below hip level the low back would be forced to flex or “round” (also known as butt wink) which creates increased pressure on the anterior aspect of the discs of the low back and can result in a disc herniation. But what about knee pain and the pressure on the knee? The debate over whether flexing the knees over the toes is good for you or not tends to center around the compression force of the patellofemoral joint (pressure of the knee cap into the femur) at greater angles of knee flexion. It has been found that the greatest pressure of the patellofemoral joint occurs at 90 degrees of knee flexion. But studies have also shown that there is a greater surface area contact between the patella and femur at greater angles of knee flexion. Greater surface area contact reduces the compressive effect on the patellofemoral joint at deeper angles therefore making a deep squat no more compressive at the patellofemoral joint then at lesser angles. A review of the literature can be found here https://pubmed.ncbi.nlm.nih.gov/23821469/.
If you do experience pain in your knees when your knee goes over your toes then the problem is most likely at the knee itself. There are several factors that can contribute to pain in the knee when flexing over the toes. It could be reduced knee mobility due to tightness of the quadriceps and or tendons of the quadriceps or weakness of the quadriceps. The goal should be to resolve the issues of the knee to allow for a knees over toes movement and then training this pattern to fortify it. How can you tell if the problem is with mobility or strength? A simple mobility test for the knee is to see how far you can flex the knee by pulling your heel to your butt. If you cannot touch your heel to your butt or come within a few inches of it then you may experience pain when the knee flexes that far under a load. To evaluate strength, compare how the knee feels when squatting or lunging with less weight or just your own body weight. If the pain lessons or resolves then it may be strength.
Another thing to consider is that you can flex the knee excessively over the toes which may cause pain due to an increased compressive force at the patellofemoral joint. If you lack mobility at the hips and or ankles you may be flexing the knee excessively to compensate for the lack of mobility at the ankle and or hips. In this case resolving mobility issues at the ankle and or hips would be the solution.
Lastly check your form. If your knee, ankle and hip mobility are normal and your strength seems reasonable for the demand you may just need to work on your form. A deep squat should be done with a neutral spinal position, your hips, knees and ankles should be flexed to allow the tiba (shin) to be parallel with your torso at the bottom of your squat. The lunge is a little trickier since it can depend the style of lunge being done. I prefer a reverse lunge where you step back into the lunge position and keep more weight on the front leg. The torso should be slightly forward with a neutral spine. The heel of the front leg should stay on the floor with the hip knee and ankle flexed so that the knee is slightly over the toes and shin parallel to the spine.