It's not the amount of innings, but the amount of pitches. In 2003, Prior ranked third in Pitcher Abuse Points. Want to know who was first? That's right, Kerry Wood! And that was through September. It doesn't include Prior's post season starts that further put strain on his arm. You can read about pitcher abuse points here. So, it's much more than innings pitched. It's the way those innings were accumulated and the amount of pitches in those innings. Ok, let's go down that path. He has basically had one year when he pitched several games of 100+ pitches. Do you recall him going into the offseason in 03 with any significant injury? He pitched in October with no problem, and then had 5 months to rest. There was not a single event in which he blew out his arm, nor has any dr or diagnostic exam found anything structurally wrong, so where is the damage? If he was damaged by 03, why haven't they found anything of any significance over the last few years? There have been many pitchers who have had similar loads that Prior and Wood (for only one season) and did not fold up like a cardboard box. Wood, is a different story, his mechanics have caused big time issues, and he has caused damage over time. Prior, is another deal, and I don't buy 03 ruined him, and if it somehow did, he doesn't have the physical capability to hold up as a starter. He was also third in PAP in 2005 . I think it's highly probable that the abuse placed on Prior is the reason for his injuries. While there are pitchers who can take that level of abuse, it is a rare breed. Furthermore, the younger the pitcher when he experiences the high levels of abuse, the greater the chance for significant injury. And the injuries that result from abuse aren't always immediate. The stress and strain placed on the pitchers body early on often have a cumulative effect and damage the pitcher down the road.