Contrary to some local beliefs, we didn't fold and we didn't screw it up. We made the post season. Not to belittle any of the other major sports, more because I never played hockey or basketball seriously, but I can't imagine a more grinding schedule than the MLB schedule. Not really for pitchers, though I certainly feel a lot different in September than I did in February, but more the position players.
If you get to the dance and play all the way through you pretty much play close to 200 games in about 225 days. Most of those off days are spent traveling or at the park receiving treatment or working on your swing or something. Deion Sanders and Brian Jordan, both All Pro NFL players and damn good major leaguers said that the ML season and the NFL season weren't even close. The MLB schedule was 10 times the grind of the NFL schedule. It's not any one thing, but the fact is, aches, pains and bruises aside, you suit up every single day and compete against the best players in the world once every twenty four hours.
Don't take that as a whine, it's not life or death, but for the guys suiting up every day it has to be incredibly tough physically, to be good.