The age old conventional wisdom that squats below the parallel, when your legs make less than a 90 degree angle, are bad for the knees. But according to Mark Rippetoe
, author of 'Starting Strength: Basic Barbell Training, this is not the case. There are four reasons why these below parallel are actually completely safe.
1. The Below Parallel (hips below the knees) squat position is completely natural for the human body. Mark makes the case that people all over the world rest in this squatting position and rise out of it without injury. The world record for the squat in powerlifting is just over 1,000 lbs.
2. Squat sets do not hurt the knees because a squat is not a knee-dependant movement. It's actually a hip movement, the knees just bend-they aren't taking the majority of the stress. It's also a back movement. The back bends forward to keep the weight of your body and any extra weight over the middle of the foot maintaining your center of gravity. When you squat correctly you drive your hips back and the knees go out to the side a little so that the majority of the force on your hips where it belongs.
3. The advice of not squatting past 90 degrees, ignores the fact that the squat does not just work the quads. The squat actually works the entire muscle mass below the position of the bar. "To maximize the amount of muscle worked, the squat must be done slightly below parallel with the knees out, the back angle in a position to keep the bar balanced over the middle of the foot, the neck in a neutral position, and the hips bearing most of the load. This correct version of the squat works all the hip muscles, all the leg muscles, all the back and abdominal muscles, and protects the knees, the spine, and the neck while allowing progressively heavier weights to be lifted."
4. A below parallel squat is one of the best exercises for whole body strength, power, balance, coordination, bone density, joint integrity, and mental toughness. Its great to make sure that you are able to squat down fully and then come up, if the weight is too heavy you need to lower it and try again.