I think a lot of people say, correctly, that you shouldn't arch your back (bend backwards) and them people get mixed up and think that means you should never stretch your back forward. I could be wrong about that, though.

I have a little pain in my lower spine sometimes resulting from a pretty painful injury I got when I was in construction survey. I had to pound a 16 pound mall a lot of the day and when I first started I couldn't swing overhand and hit the target.

So, I would choke up on the mall and bend over and arch my back a little so I could hammer in these bench marks. I realized too late what I was doing and my lower spine was so bad I was off work for a weak. That was only 16 pounds. I learned how to swing overhand pretty quick after that.

On the other hand, I have never hurt my back pulling heavy weights and allowing my back to stretch a little. I just try to keep my back and abdomen tight and not allow the stretch to slip forward. 311 is right, it's the only way to recruit the entire back, but you still have to control the movement.