Very interesting reading here .
I've been riding my entire life and have had more falls than I really care to remember. I never had any sort of back pain until I was bucked off on my head when I was 14. That pinched some nerves in my neck and upper back (spent about 3 hours laying in the field thinking that I'd broken my neck). Due to that fall and quite a few others I've had over the years, I have nearly constant pain in my back and neck, just in varying degrees. I've also found that when I ride properly without allowing myself to become tense, then riding actually helps to keep my muscles loose so the pain is diminished.
Of course, I've been going to a chiropractor frequently for the last 15 years and he's the one that keeps me going, but I honestly believe that riding helps a great deal...except the times when I take another fall .