Well, I'm actually not here to argue whether or not ATG squats are bad for the lower back or not. Of course, if ATG squats are performed with a neutral spine then it will not be harmful for the lower back. However, I find it hard to maintain a neutral spine at the bottom of a ATG squat, my hips are WAY TOO TIGHT. Any exercises to help out?
I tried working at the bottom position of the squat, by holding onto the door and pushing my hips back. But I can only maintain a neutral spine at the parallel position.