Much has been said about the potential injury risks that squats pose for the knees. Most arguments advocating this standpoint, however, lie in old traditions and assumptions which lack a sound and sensible analysis.
For some reason which beggars my belief, the arguments “Squats are bad for your knees!” and “Don’t let the knees travel over toes!” are still floating around in the fitness and rehab industry.
This, in my obseveration, has to do with the fact that both industries have not yet established what a correctly performed squat constitutes.
1 YOU ARE NOT SQUATTING CORRECTLY
The crux of the matter is that most – if not ALL – studies in the exercise science community have been looking at all sorts of types of squats - apart from the one I call a CORRECTLY PEROFRMED version: the low bar squat.
Let’s take a moment to look at the mechanics of the knees in the low bar squat:
This type of squat is a hip-dominant squat which means that the emphasis is on the posterior chain – glutes, hamstrings, erectors. These muscles make up a much larger surface area than the anterior chain of the body (i.e. mostly quadriceps) used in a conventional high bar squat with a rather vertical back angle. As the trunk angle is more inclined – or call it more horizontal – in the low bar squat, this increases the moment arm on the hips, which involves the posterior chain to a higher degree and as such takes away excessive forces from the knee joint.
With a more inclined back angle, the hamstrings perform a posterior (i.e. backward) tension on the tibia, whereas the quads produce an opposite force anteriorly (i.e. forward). Both the quads and hamstrings as such perform a co-contraction in which the forces in the knees are “balanced”. If we were to squat with a vertical back angle (the type of squat “conventional wisdom” tells us is ‘safest’), the hamstrings would go “slack” and thus would not produce a posterior force counteracting the anterior force produced by the quads. In short: a quad-dominant squat with a vertical back angle produces excessive anterior forces in the knee, whereas a hip-dominant low bar squat with an inclined back produces “balanced” forces around the knee joint.
Once we shift the emphasis from “knees” to “hips” in the squat, we develop strength in the muscles taking pressure off the knee structures. Glutes, hamstrings, and erectors absorb ground reactions forces in literally every step of our life and perform a movement called hip extension to propel our body forward. Stronger hips – less demand on the knees – better movement.
Strengthening the hips with the low-bar squat comes with another perk: the muscles and structures supporting and protecting the lumbar spine get stronger. You are literally bullet-proofing your lower back with this kind of squat. Needless to say that low-back pain is the most common physical ailment in the world of which 99% of the cases have its roots in weak musculature.
In terms of “Don’t let your knees go over your toes!!!”: have you seen how literally every Olympic weightlifter moves their knees WAY OVER their toes in the catch of a clean and jerk or snatch? With weights you and me will probably not even dream of touching? Those lifters all just seem to be fine, don’t they.
The argument for keeping our knees BEHIND our toes, as such, has nothing to do with preventing injury. It has much more to do with using a more hip-dominant motion by restricting forward movement of the knees and thus making the ascending phase of the squat much stronger. Efficiency is the argument, not prevention.
2 IN LINE IS BETTER THAN OUT OF LINE
The second consideration we have to make is to keep our knees in line with the mid-foot during the squat. To obtain this position, we need to place our stance at shoulder-width, with feet turned out roughly 30 degrees (see foto below).
This position ensures that the forces of the muscles pulling the knees INWARD (adductors, vastus medialis) and OUTWARD (external hip rotators, vastus medialis) perform yet another system of balanced forces around the knee joint.
If the knees travel in line with the INSIDE of the foot, the external rotators of the hip are switched off, which makes hip extension (the primary motion for coming out of the lowest position in the squat) ineffective and weak. If the knees are “opened” too much, the weight shifts to the outside of the feet which then start rolling over the outer edge. This would make the squat less stable and much weaker. No-go.
In simple terms: we want to have our weight balanced on the entire foot during the squat, with knees “pushed out” and traveling in line with the middle of the foot (see foto below).
3 SETTING THE KNESS EARLY
The third consideration we have to make is to set the knees into the right position at the right moment in the descend. Timing is, as they say, everything.
As we initiate the descend with a double-bend (i.e. hips and knees) as well as a forward-lean in the trunk, we want to “freeze” our knees at that current angle while squatting down. This doesn’t mean that the knees won’t continue to move forward as we descend. They will. However, there is a difference between letting the knees travel forward freely with no end in sight, and letting them go forward a little more as we keep squatting down. This is a natural mechanism which allows dropping our hips below our knees and maintaining stability and balance in the whole body. If we were to hold the knees back too much, our centre of mass would shift towards our heels, and our lower back would start rounding in order to obtain a greater range of motion. Both are mechanisms we want to avoid for obvious reasons.
As a gross orientation, the knees should travel no further than into vertical alignment with the toes. This will vary with anthropometrics, and it ensures that the knees are kept in the correct position.
In summary, squats performed the correct way – low bar position; forward-lean; hip-dominant movement; restricting forward movement of the knees - makes our knees stronger and healthier.
And that’s all there is to it.