I've read in a few places that it is important to not let the knees go past the toes while squatting. Where did this idea come from and is it really a big deal?
In general, not letting the knees go past the toes is spot-on advice.
The danger of letting the knees drift forwards of the toes is that a dangerous amount of shearing force is applied to the knee joint, increasing your chances of injury.
Avoiding Knee Injuries While Squatting
The origins: In the 1950s, physical therapists testing cadaver knees identified and calculated the varying forces at different joint angles of knee flexion.
They concluded from their results that certain positions maximally stressed the soft tissue (ligaments and tendons) of the knee, thereby exposing the joint to unnecessary danger.
And leg extension machines have been stricken from physical therapy regimens ever since.
Leg extension machines are bad because they do not allow you to actively select your range of motion and they increase the risk of knee injury because all muscles that cross the knee joint are not utilized
The leg extension machine is an exercise device that targets quadriceps muscles, which can be found at the front of the upper thighs.
Most gym machines such as leg extension machines target only one aspect of a multi-joint exercise, and the leg extension machine is a prime example of a machine that falls short in this regard.
Since then, numerous studies have shown the limitations of these cadaver models (since cadavers are, well, dead, they have no blood flow and thus cannot “warm” the soft tissues, which accounts for a lot of the “dangers”) but old myths die hard.
Now, based on decades’ old research, that information gets distilled to you in 2020 as “don’t let your knees track past your toes, or else!”
So now you know how this piece of exercise advice came to be, and that while letting your knees track too far forward does place more stress on the knees, it’s not inherently bad.
That being said, here is a list of the real reasons…
Reasons You Don’t Want To Let Your Knees Go Past Your Toes
(i) Letting the knees pass your toes promotes balancing the weight on the balls of the feet, instead of the heels (where it should be), minimizing your ability to produce force and compromising your ability to lift appropriately heavy weights.
(ii) If your form is loose enough that you allow your knees too far forward, you’re likely not maintaining proper back position (neutral lumbar curve) and letting yourself slump your shoulders too much. This is a big no no.
(iii) The more forward your knees are, the less your glutes and hamstrings can contribute to squatting.
Not only does this limit the weight you can use (and benefit from), but it also destabilizes the knee (since the hamstrings are a huge contributor to knee stability).
It’s not the position itself that’s dangerous. It’s the other form discrepancies coupled with the increased forces (read: weights) of the position that is dangerous.
This is exactly why you’ll see some strength coaches allow their taller players to squat with their knees drifting forwards.
Under a coaches’ watchful eye, they can minimize the chance of injury through careful scrutiny and instruction.
What does all this filibuster mean to you, dear reader? Easy:
Don’t let your knees pass your toes when you squat.