In the very beginning of this video, Dr. McGill* is using a simulator to create a disc herniation by merely flexing and bending a spine repeatedly, in a movement that resembles a sit-up. The rest of the video shows how to perform his 3 basic exercises for strengthening the abdominal muscles without injuring the back (modified curl-up, bird dog, side plank).
Here he is discussing myths about exercise. Did you know that sucking in your stomach is harmful? It can cause the spine to buckle (a sideways deflection).
He says that a flexible back or a strong back are not protective of back injury. In fact, they are associated with more injury. The muscles of the back are meant to stabilize, to prevent movement. This is true for abdominal muscles and others of the core or torso. However, since back and stomach muscles are in constant use, they need to be maintained to provide endurance.
Here’s another video showing McGill’s “Big 3” exercises for stabilizing the back:
What I am learning – over the years! because this just isn’t sinking in – is that repetitive motion is not your friend, especially if it is done with weights. It damages wrists, elbows, necks, knees, and backs. The above three exercises are low-impact and non-repetitive.
* Dr. Stuart McGill is a professor emeritus at the University of Waterloo where he taught for 32 years. His research involved how the back functions, how it becomes injured, how to prevent injury, how to rehabilitate an injured back, and how to enhance athletic performance. His clients include professional athletes. He currently serves on the editorial boards for the journals Clinical Biomechanics, Applied Biomechanics, and Spine, and is the author of several books.