I just watched a segment on Entertainment tonight on Terminator 3 and they had a short interview with Arnie... he was asked whether he's going to be appearing nude in this sequel (due to the whole time travel process) and he said yes, that he works out everyday in order to achieve the same body he had in 1984 because the terminator endoskeleton and mold and whatnot are still the same.
Even though I don't agree that his body looks as good as it did in '84...he does look pretty damn huge, especially for 55. You guys think he still juices it? His test levels are a lot lower now than when he was in his prime... and yet he still has achieved and maintained a fantasticly huge physique.
On a side note - I believe this movie is looking to be total shit... the franchise just needs to be given up (on close-ups and without the glasses arnie looks just too old to play a convincing T-800 in my opinion).