Ok, since I sounded like a jerk in that last post: Heelhooks can damage stuff in the knee that I don't know about, but I once got decently bad ankle damage from a heel hook. It was to what looks to be labelled the "peroneus longus" in this picture: http://www.orthogastonia.com/patient_ed/images/ankle/ankle_osteoarthritis/ankle_osteoarthritis_anatomy03.jpg because even when it didn't hurt to stand up on, I'd rotate to the outside on that side my ankle would give out and I'd fall over. I found this out in my university's chemistry lab. Glass, chemicals, you name it, it wasn't pretty. The calf crush that I know doesn't target a joint or a tendon or anything, it just squeezes the calf really hard. I only do it in counter to an achilles lock, because it seems like a * pro-wrestler move that just causes pain. I don't know what would happen if I did it really hard. Deep muscle bruises?