And here he is, clearly having spent several months at the gym, for his rƓle as King Leonidas in the forthcoming graphic novel adaptation "300", coming to cinemas worldwide from March 2007:
The film has a very heavily processed look, and was shot almost entirely in blue-screen and green-screen environments [click to see the trailer], so it's difficult to discern precisely to what extent Gerard might have been 'enhanced'.
However, the two images below, taken under (relatively) normal conditions on the set during the filming indicate that at least some of the musculature is his own: