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Google Dr. Stuart McGill and his “Big Three” exercises and then go down that rabbit hole on YouTube and the web. He’s done many fascinating studies on spines in his lab and he’s written several books that explain it all in approachable terms. One thing he preaches is never to do another sit-up in your life... and he backs it up with intradisc pressure instrumentation that illustrates it’s one of the worst things you can do.
In a nutshell, the spine needs to stay in a good position anchored by core stabilizing muscles; not wobble around due to either lack of core or from stretching into challenging positions.
Changed my life- without exaggeration.