First—Are you naturally built for back squats? Long or short legs? You could use the “Wall Test” to give you an idea. Face the wall with your toes about 6 inches away from the wall (normal squat width of the feet), while keeping your chest up and out with your shoulder blades tight and pulled together and a tight arch in your lower back (your arms should mimick holding a BB on your back), descend down as low as possible while maintaining that tight arch in your back.
If your able to sit down past parallel, the forward translation of your knees don’t prevent you from getting to depth by coming into contact with the wall, and your heels stay flat, you’re probably just fine to back squat.
**Just because you don’t pass the wall test, doesn’t mean you can’t or shouldn’t back squat. It will give you an idea of the problem areas you need to address…losing your lower back arch, ankle flexibility, chest posistion, etc.
Second----where are you placing the bar? High on the traps, low, traditional? This can make a big difference. That’s one of the main problems with those neck rolls people put on the bar while squatting, it automatically puts you in a bad starting position by forcing your head forward.
I’ve found that squatting without any shoes to help me keep awareness of where my weight is on my feet, as well as keep them flat to floor.
I have also found the “Dophin out of the water” image to be helpful. By looking up while coming out the hole, you automatically keep your path more vetical…the head follows the eyes and the body follows the head.
What are you trying to accomplish with your back squats? Are they necessary to reach your goals?
Third—Do you keep your elbows tucked, tight, and below your shoulders as you descend and then ascend. If you’re letting your elbows rotate backwards, it’s going to force your torso into a forward lean.