Correct technique, though, is crucial. Squat movements are complex with many variables involving ankle, knee, hip and spinal joints. Improper technique and incorrect exercise prescription can cause muscle and ligament strains plus ruptured disks as well as instability, slipping or displacement of a vertebra.
I was happy to find a recent study investigating how to optimize muscle development while minimizing injuries.
- During the squat, the spine is most vulnerable to injuries
- To maximize development of your quadriceps, squat down to parallel, i.e. your thighs are parallel to the floor and hips do not go below knee level; going lower provides no extra benefit
- Take a wider stance to optimize your hip adductors and extensors; this also reduces shear forces on your knees
- A front squat will place noticeably lower compression on the knee and lumbar spine compared to a low or high bar back squat
- Position your feet in a comfortable stance that lets the knees move in line with your toes
- Sit back into the squat while descending and don't push the knees forward over your toes
- Your descent should be controlled with a two to three second tempo
- Align your spine properly by gazing straight ahead or upward, keeping the spine as upright as possible and avoiding any movement from side to side
- Avoid going deeper than 90 degrees (thighs parallel to the floor) to protect your knees, unless you have athletic goals that benefit from a deeper movement
- If you have knee injuries, descend only 50 - 60 degrees
- If your heels rise off the floor during the downward movement, try placing a barbell plate under the heels to help with stability
Source: J Strength Cond Res 24(12): 3497-3506, 2010