"A child does not learn to squat from the top down -- in other words, he does not one suddenly make a conscious decision one day to squat. Actually, he is squatting one day and makes the conscious decision to stand."
- Gray Cook
"More squat myths?!?
We???ve all heard it, if you dip below parallel during a squat, your kneecap will blow off and land in the front desk girl???s mocha latte. Well it just ain???t true! What???s that, you need a little more evidence? Ok boys and girls, its time for today???s episode of Fun With Musculoskeletal Anatomy.
The knee has four main protective ligaments that keep the femur from displacing on the tibia (ACL, PCL, MCL, LCL). These four ligaments are most effective at their protection during full extension and full flexion. Full extension would be when you are standing; full flexion would be when there is no daylight between your hamstring and your calf. When the knee is at 90 degrees of flexion (the halfway point), these four ligaments are almost completely lax and cannot exert much if any of a protective force at the knee (Zatsiorsky V. Kinematics of human motion. 1998 - published by Human Kinetics - p.301).
Unfortunately, the position where the protective ligaments of the knee are not doing any protecting is the common recommended stopping point of a squat. Therefore, as it as it turns out, this is the exact worst place you could reverse the motion under load.
If flexibility allows (heels staying planted, torso not flexing forward past 45 degrees), then a full squat where you lower yourself all the way to the ground is far safer on the knees than the traditional half squat. Guess what joint angle most leg extension machines start at? If you said 90 degrees, give yourself a pat on your healthy knee. This makes a full squat even safer than a leg extension machine (Wilk K et al. A comparison of tibiofemoral joint forces and electromyographic activity during open and closed kinetic chain exercises. Am J Sports Med; 24(4):518-527).
So am I telling you never to do parallel squats? No! Am I saying that you???ll injure yourself on a parallel squat? No, again! What I???m trying to do is simply make an argument for the safety of full squats, thereby relegating squat myth #2 to the fiery pits of hades."
- Marc McDougal