The depth of a squat is determined by the individual’s capability and then by the requirements for their sport/function. Some sports don´t require a really deep squat and some sports do. You always want to keep in mind that, even though a sport requires a specific range, if you are not able to go through that range yet, it is always best to progressively move to that range instead of trying to jump through the range while the body is not mobile, stable or has enough motor control yet. It is very important that we don´t rush ourselves to hit a specific movement standard.
For CrossFit, a squat with the hip crease below the knee joint is optimal due to the requirements of the sport. CrossFit requires individuals to be able to snatch 1 rep maxes and catch it really deep, the sports requires individuals to be able to do a max height box jump. But that is not the case with, for instance, basketball. With basketball, individuals are required to be explosive, quickly. Most basketballers will almost never go below a 90 degree angle squat, so it´s not a big priority for them. That does not mean they should not do it or they can´t benefit from deep squats, it´s just that it translates less to their sport than partial squats. It´s like training for a running marathon, by biking everyday, off course it will help but it does not translate very well to the actual function.
So a few common things we see happening with individuals who try to go through a certain range that they are not ready for.
1. poor core tension in a specific range
Poor core tension is something that can cause a lot of issues in the spine. We want individuals to be able to brace the abdominals and stabilize the pelvis/trunk while descending and ascending. If that is not the case, there will be a lot of movement at the spine which oftentimes result in a tightening of the lower back. Make sure you can go down into a squat and maintain proper core tension throughout the entire range that you go through, especially when you are axially loaded.
2. poor foot positioning/knees caving
Poor foot stability is a common issue we encounter. A hypothesis is that individuals wear shoes that don´t allow for a lot of movement in the foot/foot sole which removes the necessity of foot to stabilize because the shoe does all the work. Poor foot stability oftentimes causes the knees to cave in a lot, poor mobility in the ankles/hips can also be the factor that hinders individuals from performing a proper squat. Always make sure that the knees are in line with the toes.
3. pelvis tucking under
The infamous butt wink, this is a much-debated topic. A lot of coaches swear that it is not harmful and a lot of coaches swear that it is, we believe an exaggerated butt wink can be harmful when axially loaded due to the requirements of the lumbar spine to remain unmoved. A lot of times a butt wink is a result of bad ankle and/or hip mobility, poor core stability (example 1), bad motor control (coordination).
4. shifting hips
It takes a lot of reps to undo certain errors in the motor pathway, certain issues like a hip shift will not be felt right away so a lot of individuals don´t think it is a priority. After a few years, they start having pain on one side or another and come to the conclusion that the hip shift is the reason behind that pain. The problem now is that they fed the compensatory pattern so much, it becomes really difficult and takes a lot of time to undo that way of moving. So although every individual is asymmetrical and that it´s quite normal, we do need to strive for symmetrical movement and posture to reduce the risk of injury and make every part of our body stronger instead of only making them stronger parts even stronger.