I have a predisposition to RSI. My carpal tunnel was so bad by my late teens/early 20's that one doctor recommended bilateral surgery. Then I:

* Started taking large doses of B12 and B6 * Switched to Dvorak layouts on all my computer keyboards * Got a good buckling-spring keyboard * Gave up ballpoints, gel pens, etc. in favor of fountain pens * Gave up writing looped cursive (the way almost all American children are taught to write in school), learning to instead use Getty-Dubay Cursive Italic hand

Now I'm 30, and have no problems with carpal tunnel despite never having had surgery.