well TEd, Ripped is right next to Rep in "Bodybuilding Jargon"..

Ripped:
A condition of extremely low bodyfat with superior muscle separation and vascularity. Variations include sliced, cut, and cross-straited.

seems like there could be a transferral from Butcher's Jargon here. <g>

edit - Dr. Squat has it thusly:
Ripped -- Slang meaning extremely visible muscularity resulting from both hypertrophy and subcutaneous fat removal.

removal by ripping??

edit[2] - maybe there's a drug (e.g., steroid) connection, as in "man, are you ripped!"? <g>