The biggest connection I see between body builders and entrepreneurs is discipline and ambition. Deciding that you're going to maximize your body's potential is quite similar (in spirit) to deciding to maximize your earning potential.

I think body building is about 100x easier though. Unless you're aiming for a pro card, there's really no uncertainty to deal with. That's the toughest part of entrepreneurship. There is no formula for success. Imagine exercising and eating according to a plan for 3 years and then ending up obese.