For what it's worth, my son didn't fall into any of those categories. Never saw 90mph a day in his life. Never was "the guy" where he would eat up innings and get overused. Told by most folks that he had pretty solid mechanics. It just shows (in my opinion) that there are different reasons for different folks to have TJ. The one thing that is a fact though, is our arms are doing something that is completely unnatural for the arm and over time, this unnatural action will catch up to you.