I get this question a lot. People always notice that I squat deep and all my clients squat deep, and the subject always comes up about the safety of deep squats.
There are many factors that contribute to knee health, and certainly if you can’t squat deeply without pain, then you shouldn’t (immediately) do it. The causes of knee pain need to first be identified and addressed. Things such as muscle length-tension relationships with regards to the lateral quad and rectus femoris muscle. Often when either of these two muscles is too tight, there can be some associated knee pain. Another cause of knee pain is poor patella (kneecap) tracking, which is often caused by vastus medialis weakness.
Further, the quality of all the soft tissues of all the muscles that act upon the knee during squats should be assessed. If movement is restricted in the hamstrings or adductor muscles, or if the glutes aren’t firing properly, these are all issues that can cause knee pain.
So clearly, just because you can’t squat deeply without pain doesn’t mean you shouldn’t do it, but rather that you have some other problems that need to be solved first.
With that in mind, let’s look at whether a deep squat is actually dangerous or not in an otherwise healthy pain-free knee.
First, when you squat to a height above parallel hamstring involvement is limited. Without sufficient hamstring involvement, the primary anterior translation restraint becomes the ACL or Anterior Cruciate Ligament. What this means is that when your squat depth ends while the hips are still higher than the knees, as the quadriceps pull strongly to deccelerate you and then push you back up, the ACL bears significant stress.
In contrast, when you squat to below parallel, so long as you make an effort to avoid forward knee travel past a vertical line (approximately) above the toes, the hamstrings come to the end of their functional range of motion, and the pull tightly on the back of the tibia, thus becoming the primary source of restraint to tibial anterior translation. This relieves the ACL of such associated shear stress.
There is a mechanical truth that the greater depth you squat to the higher the compressive forces on the back of the kneecap, and this is often taken out of context in locker room discussion. Firstly, there are hundreds of thousands of people around the world at any given point who are deep squatting 600-700 lbs, and their kneecaps are doing just fine. Folks who have premature deterioration of the posterior patellar articular surfaces would know early on that squatting deep was not good for them. But this group of pe0ple is small compared to the general population.
The number of people I see at the gym who are squatting above parallel with far heavier weights that are quite risky at best to their low backs as well as to their knees would be much better off at the very least halving the weight they lift and working on performing a correct deep squat which involves the hamstrings, glutes, adductors, and quads as opposed to their current high-risk quad squatting.
All you have to do is see for yourself. The people who complain the most about knee pain are above parallel squatters. Those who squat full depth rarely have knee pain because all of the muscles that act upon the knee joint are being used together to compress and support the knee joint properly.
Finally, if you are someone who has trouble squatting deep and you want to learn how, there is a method to learn the movement. You should speak to a qualified trainer who knows how to teach squatting correctly.