"To Crunch or not to Crunch: An Evidence Based Examination of Spinal Flexion Exercises, Their Potential Risks, and Their Applicability to Program Design"- Contreras, Schoenfeld JSCR 8-11.
I probably have disagreed with every article these two guys published. Which is why its important never to throw the baby out with the bath water sort of speak. I have to admire this work, they really took on some sacred cows regarding spinal flexion exercise in general. They make a lot of great points...
"The studies in question attempted to mimic the loading patterns of occupational workers by subjecting spinal segments to thousands of continuous bending cycles, which is far beyond what is normally performed in the course of a normal exercise program".
They also note research by Battie & Videman which indicates much of disk injury to be related to genetic factors and not exercise.
They note that many of the en vitro spine studies involve porcine models (which have very different mechanics than the human spine), or human cadaveric spines with most of the supportive structures removed.
They conclude by saying that based on current research its premature to conclude that the human spine has a limited # of bending cycles...and variety in spinal loading is associated with a lower risk of spinal pathology. And you want to do a good warm up before doing spinal flexion exercises early in the morning, or after prolonged periods of sitting; or save them for later on in the day.
Great work guys.