Years ago I worked a few hours a week in the fitness room of a local rec center. I was there to help newbies learn how to use the equipment properly, tidy up a bit, and make sure meatheads shared the chest press benches. I was also on the lookout for anyone at risk of injuring themselves. One day there's a guy loading up the preacher curl machine—a completely ridiculous machine IMO, that mimics nothing in real life—with waaayyyy too much weight, rounding his back and grunting away. Now here's a guy definitely at risk of injuring his back, i.e. a bulging or herniated disk in his lumbar spine. I gently offered up something like, "Hey, how's it going? Be careful there. You're putting your low back at risk by. . .." I got about that far and he barked at me, "I've broken my back three times! I know exactly what I'm doing!" Whoa. Ok then. You are correct sir, you DO know exactly how to break your back. Well done. I said this in my head, of course.