You know how I know? I've been doing it for a while now and all it leads to is sweating and me screaming "OH MY GOD" and trying to move as little as possible.
OK, that last part only happened once. Friday, I picked up boybat's towel from the changing room and my spine twisted into some double helix pretzel shape that it hasn't untwisted from yet. Good God, throwing your back out really freeking hurts.