Years ago when I used to do anything like the 45 degree ab crunch machine thing, my spine would crack on every contraction. I was aware eventually this could pr

Years ago when I used to do anything like the 45 degree ab crunch machine thing, my spine would crack on every contraction. I was aware eventually this could probably cause some serious problems, but this type of exercise is also really good for the abs and entire core since it is a sort of modified active plank. I actually resolved it using dead hangs. Nobody told me to do that, but it seemed clear to me that things weren't aligned properly, and this was an obvious way to balance the strength on both sides so the spine stays straight when doing those kinds of contractions. Gravity is your friend. It worked. I haven't had that problem since.