You’ve probably read and heard it many times: keep your knees behind your toes when squatting! Widespread fitness advice for many years, which you may also have heard enough times to be a persistent myth. What is true?
Let’s say it’s anatomically impossible to squat as deep as possible without your toes extending past your knees. So the rule that your toes should not extend past your knees effectively prohibits the deep “ass to grass” (ATG) squat. That’s the way you see weightlifters squat. So the discussion basically revolves around squat depth.
One of the most quoted scientists when it comes to this subject is Tom McLaughlin, of Duke University in the US. He and his fellow researchers found in the 1970s that if the shin bone remains in a more vertical position when knee bending, there is less shear, or shear stress, placed on the knees. This led to instructors and trainers worldwide advising their clients not to squat with their knees past their toes.
LIMITED SQUAT STYLES
There are basically two ways to make sure your knees don’t go past your toes on the squat. ‘Restricted’, or restricted squats, so to speak.
The first is by severely limiting your squat depth and performing a sort of quarter squat. This limitation of the range of motion (ROM) is not only at the expense of the effectiveness of the exercise, but is actually taxing on the knees.
The second way is by squatting in a more or less different way and performing a hip dominant (power) squat. In this way of squatting, you don’t squat so much, but sit back. There is more hip flexion and less knee flexion, and you squat to about parallel. That is, until your thigh bone is horizontal and you can put a glass of water filled to the brim on it without spilling. To keep the weight above your center of gravity and balance, tilt your torso further forward on this execution. By squatting in this way, you involve the strong hip muscles and your lower back more in the exercise, and you limit the involvement of the quadriceps: the muscle at the front of your thigh that you aim to train with conventional squats. In fact, this way you turn the squat into a hip exercise. Is there something wrong with that? In principle not, although you do put a lot of pressure on the hip joint (which we discuss in more detail in the section ‘Research’). And if you mainly want to train the quadriceps, it is certainly not the optimal way of squatting.
In ‘normal’ squatting, your knees also come (well) past your knees. So this is completely natural. Now the obvious question is how natural it is to squat (squat) with one and a half or twice your body weight on your shoulders. But if you ask us, this is first and foremost a matter of progressive overload and adaptation. In other words, gradually increasing the training intensity to give your body the chance to adapt to the increased stress.
But what does science actually say, after Tom McLaughlin? Well, actually, there’s no evidence to back up the “knee behind your toes” claim.
Let’s do some research. You may have seen the picture of the squatter with the wooden bulkhead that keeps his knees from going past his toes. In fact, that’s the hip dominant squat we just described. The recording comes from a study to this specific topic by Andy Fry et al. from 2003. In addition, in seven recreational strength athletes, the effects on knee load were measured with an unrestricted squat (with the knees past the toes) and with a (literally) limited squat. It was found that doing unrestricted squats increases the pressure on the knees by almost 28% compared to limited ones.
But there is also something going on the other way around: with the limited squat, the pressure on the hip joint is no less than 973% (!) greater than with the unrestricted squat. This is because limited squats require the torso to bend further forward to avoid falling backwards. That enormous pressure on the hip joint immediately affects the lower back and that does not make the limited squat better or healthier than the unrestricted squat. Rather the contrary. The researchers about this:
Exercise technique guidelines should not be based primarily on force characteristics for only one involved joint (eg, knees) while ignoring other anatomical areas (eg, hips and low back).
ASS TO GRASS SQUATS
And what about the ATG squat? For this, too, studies tend to favor it. There is no evidence that deep squats, in normal circumstances, are bad for the knees, as you can read in a meta-analysis by Brad Schoenfeld, among others. In a 2013 study from Sports Medicine, the deep squat is considered even better for the knees than the parallel. Because, simply put, the more you bend the knees (so the deeper your squat), the less pressure there is in the knees. ATG squats are also the least taxing on your lower back. The researchers therefore conclude:
(…) The deep squat presents an effective training exercise for protection against injuries and strengthening of the lower extremity. Contrary to commonly voiced concern, deep squats do not contribute increased risk of injury to passive tissues.
However, there is an important condition attached to that conclusion: your flexibility and mobility must allow you to squat so deeply. If that is not the case, you will automatically round your (lower) back as you sink deeper: fodder for nasty injuries.
Looking purely at muscle growth, deep squats are not a must, unless you explicitly want to train your buttocks: full squats appear to be effective butt builders .
Squat lower than parallel only if you are confident your execution is correct, i.e. without a butt wink. But that can really only be judged by a spectator. Or you have to make a video recording of your squat.
There are many squat styles. Probably your main goal is to get bigger quadriceps and then you will benefit the most from a high bar squat with parallel as the minimum squat depth (or minimum ROM). Squatting deeper than parallel is also allowed – for training the quadriceps this probably makes no difference, but you may stimulate your glutes more. However, only squat deeply if you are sure that your mobility allows for a correct (straight) position of your lower back.
Squatting to minimal parallel, let alone ATG, automatically means your knees are past your toes. This puts slightly more pressure on your knees than with a limited squat. That is not a problem, according to scientific research. Your body adapts to the increasing knee load, provided you build it up slowly (so don’t use too much weight too quickly). In addition, the unrestricted squat puts much less pressure on the hip joint than the restricted one.
Please note, the advice in this article only applies to a healthy person without knee problems!