Originally Posted by RedsManRick
I would hypothesize that we're still in a place where we're over-genericizing things. While training, nutrition and bio-mechanical analysis have improved, the human physique is still essentially what is has always been. I would imagine that pitching is much like any physical activity and repetitive use injuries (even those that culminate in a traumatic event) are in large part of a function of the specifics of a given pitcher's body -- it's "design", it's recovery rate, etc.
One thing not taken in to account is the selection effect. If pitchers in the 60's were expected to throw 300 innings, the ones who were particularly susceptible to repetitive use injuries were more likely to get injured via overuse early in their baseball careers, lose effectiveness and fail make/establish themselves in the major leagues to begin with.
Would Rich Harden or Mark Prior have "survived" long enough to make the majors in 1966? It's possible that the pool of major league pitchers 40 years ago had already been filtered of it's most injury prone pitchers, making it appear that the average pitcher had greater ability to give innings. It's also quite possible that a number of pitchers today could be 300 inning guys were they given the opportunity to do so.
Add in the lack of the slider, an extremely stressful pitch to throw, and the increase of power throughout the lineup requiring a more sustained effort of the pitcher and it's easy to see the variety of explanations adding up.
This is an excellent post Rick. Even recently there are very good examples of playing it safe and taking things by the book and they work out for some and not for others. I can never see Strasburg being a 300 IP horse without breaking down, but I could see Verlander being a 300 IP horse and not breaking down. I think the toughest thing to determine is going to be how to tell which pitchers can handle what, is it mechanics, body build, etc. Until that happens, if it ever does happen, I get the feeling no side of this argument will be completely right or completely wrong, its likely somewhere in between.