Stuart McGill is often quoted in these matters, as he has done extensive studies on the mechanics of the spine.
http://www.dailymail.co.uk/health/article-440309/Is-Pilates-...
http://www.amazon.com/Back-Disorders-Second-Stuart-McGill/dp...
http://www.t-nation.com/free_online_article/sports_body_trai...
http://www.t-nation.com/free_online_article/sports_body_trai...