ASMI had a video a couple of years ago (maybe more but that's when I got it) that discussed cadaveric studies on the UCL. They stated that the breaking point for the ligament was at about a 3rd of the stresses that pitching puts on it. The moral of that story was that, in order for it to not fail on every pitch, the muscles, tendons and ligaments around it must contribute significantly. This is one reason why some say that early pronation protects the UCL. The pronator teres muscle runs nearby and pretty much parallel with the UCL. Early pronation is said to take some of the load away from the UCL because it activates that muscle more. Thanks to Chris for that description. It seems to make sense.