There are a couple of issues at play here. It is possible that Prior was overused a few years ago he was very young and just starting out, at the college level guys do not play as long a season and so a lot of times their arms haven't been conditioned to the strains of a long major league season yet, so it can be important I think to not over use them right away, because I think it can cause problems but that I'm sure is a player to player issue and it could be what has been wrong with Prior. It is a fact that Wood was over used at the highschool level which has led to his arm problems. As for position players I think one of the biggest current factors in todays game for injuries is guys are just big and more muscular than they use to be and when you have more muscles, you have more muscles to hurt. Conditioning should be very important and guys should be staying loose during games by riding a stantionary bike etc. to prevent their muscles from tensing up, which would cut down on hamstring injuries etc. but most of them don't do it.