I think this is my confusion: contracting the quads straightens a bent leg. Contracting the hamstrings bends a straight leg. Contracting the glutes and lower back straightens a bent back. Contracting the abs/upper thighs bends a straight back. <--- this might be greatly simplified, but this is how I understand it.
So, when I am in a full squat position my back is bent and my legs are bent so It seems that the quads straighten the legs and the posterior chain straightens the back. I feel like the quads are the prime movers in this action and the lower back and glutes are just straightening out the back as the quads push up. So it seems that trying to activate the posterior chain more would just result in doing a good morning, which I am pretty sure is not correct squat form.
Can anyone help me out understanding this? I feel like I am just missing some important aspect of what is supposed to be happening. The only thing I have found is an article that says to come out of the hole by forcing your chest up and your back into the bar first when you come up and not to think about pushing your heels into the floor,but I have heard the opposite also.