[ehmish]

I've got a friend who went into the trades instead of going to university, he (correctly) recognised that what he was passionate about wouldn't even pay for the degree (composing music) so he figured he'd do it on the side and do a trade to earn a living. Unfortunately due to a workplace accident he cut the tendons in his wrist with a box cutter, which means he can't now play the piano for any reasonable amount of time. So i guess it's less "the body wears out" but more "you accumulate a lot of small injuries that eventually prevent you from perfoming your trade"

Edit:typo

[WalterBright]

I'd buy the cumulative injury theme, but not the exercise part.