While in the loaded position, the shoulder and elbow bear the equivalent of about 40 pounds of force pushing down. When the ASMI biomechanists wanted to know how much more force an arm could take, they brought cadavers into the lab and pulled and pushed upon the elbow joint to find the breaking point. The cadavers's ligaments blew apart just after 40 pounds of force. "So a pitcher is just about at the maximum," Fleisig says.
There are two things I wonder about with this. One, how much variation is there from person to person in tendon strength? And two, how much can working on your countering muscle groups help?
The first, I wonder about, because the people achieving things at the extremes of human accomplishment are people who are physiologically different, in most cases. There was an 800m woman runner this year who destroyed the field, and there were comments made that she had an unfair advantage because of an unusually high testosterone level. While I wouldn't argue that that testosterone wouldn't help her, the idea of banning her from competition because of it (it was suggested) is absurd. Unless there's a reason to believe that that testosterone level was achieved by chemical enhancement (and I've not heard even the vaguest of intimations that it was), then it's just a natural advantage.
Competitors in sports get those kinds of natural advantages all the time. To get back to baseball, and specifically pitching, banning her for that would be morally equivalent to MLB banning anyone over 6'10" (or pick some arbitrary height) from pitching. Even getting back to that article, there was a note that Prior was liked because of his size. Same thing.
There was also a note in the article about sprint times improving so regularly. And Usain Bolt certainly makes it look easy, no question. But it's rather amusing when compared against this article on Bolt. (And as a side note, how frickin' cool is it that the man's name is Bolt? Makes me wonder if that name was what got him started in running.)
And getting back to the other point I mentioned, I read a long time ago that if you wanted to improve a specific action (say, placekicking ability), the key was not to improve the muscles that power that action. The key was to commensurately improve the muscles that counter that action at the same time. Because your body won't let you push harder than you can stop that push. Or at least that was the theory. I wish I knew more about that.