In photographic terms, probably what you want what is called a "butterfly" lighting pattern. It's named this for the butterfly-wing shaped shadow it creates under the subject's nose, like here
. This pattern is commonly used to light for models, head shots, etc because it's very flattering while at the same time still open enough to see all the details. I would assume it works exactly the same for lighting muscle.
Ideally you want one very large bright light, and as Jeremy said you essentially want it up high, directly above the camera. If it's high and to one side or the other of the camera you won't get the same effect. (Shadows will fall differently). You (or your subject) should then be directly in front of the camera, facing it. Turned slightly is obviously okay.
That is the ideal setup, for it to look natural you want a single large light source to emulate the sun. Unfortunately many of us don't have access to a light source large enough to light us from head to toe, that we can somehow place high above the camera. For the after shot in this thread
I had to use multiple light sources.... that's obvious by the fact that I'm casting multiple shadows. But it worked for my purposes.
Main things are, try to light yourself from high up and straight on (not off to one side), with enough light, and have the light cast evenly from head to toe. This should produce the results you want.