gymtime-the greatest potential to injuring your spine is an excessive forward lean.Thats why it is recommended to stay fairly upright when squatting.Take the gerard trap bar.That allows you to remain upright with no forward lean and more weight can be used but I've never experienced or heard of it causing any excessive force on the spine.That's one of the primary reasons it was made.As for front squats,when you have the bar positioned correctly with the elbows held high you don't feel the forward pull of the bar that much because it allows you to remain more upright compared to the pressure of a back squat where the pressure of the bar on your upper back forces you to lean forward.Try these out sometime and you'll see what I mean.Also, I'm talking about a front squat using a clean grip, not the kind where you have your arms crossed over one another and try a balancing act with the bar.I have seen many people do them in this manner and they are so busy trying to balance the bar, they can't maintain correct posture.