A common discussion in the strength and conditioning community is the proper squat depth. Should it be a quarter squat, powerlifting squat, ATG, etc.…?
The evidence is clear for any movement that we perform, a greater range of motion(ROM) leads to increased muscle fiber use. However, the squat is one of the few exercises that I would sacrifice ROM for safety.
I always recommend my athletes to descent down until their femur(thigh bone) is parallel to the floor, also known as ”powerlifting parallel.” Because when we squat below parallel, there are some injury concerns.
Karl Klein, author of The knee in sport, said, ”in the full squat position the posterior rim of the medial cartilage is locked down between the tibia and the femur... If any disruption of the mechanics of the joint takes place at this time... a posterior tear results.” What he's saying is that if a slight adjustment takes place in the bottom part of a deep squat, an injury will most likely occur.
Not only that, but another common problem is a posterior pelvic. As I demonstrate in this video, you can see as I go below parallel, my pelvic goes into a posterior tilt. This creates a great deal of pressure on the anterior side of intervertebral discs in the lower back. Once again putting us at risk for injury.
Also, it is rare to see a sport that utilizes the full squat depth, i.e., go below parallel. Olympic lifts are more or less the only sport that will do that. So why take the risk if you don't have too?
Bottom line: It is still possible to develop great leg strength without taking the risk of going to deep into the squat. If you're not an Olympic lifter, I will recommend you to go thighs parallel to the floor as you descent into the squat.