Perlman claims it's his body, resulting from HUGE amounts of training, but I'm not so sure!!
It's not him, that was the joke. He was kidding I think. Here is his serious response:-
CD: Could you talk a little about the prosthetics they put on you when you're Hellboy bare-chested?Perlman: Well, first of all, it's really, really gorgeous to look at...very sexy, anatomically, like Leonardo da Vinci in terms of its accuracy. The things that are amazing about Rick Baker's work is that it serves all masters. It's very comic book, yet incredibly life-like and just never calls attention to itself. And it enables me, and I have pretty lousy posture, I'm an older guy, I'm not like a 23 year old hunk, that it enables me to stand naturally, and I'm just gonna look perfect, no matter what I do. And it goes for the body as well as the face. If I overact, the mask takes the stink off. If I under act, the mask takes the stink off. There's a truthfulness about it, and I don't know how they achieve that, but I do know that whenever I look at any kind of playback, I think 'Man, I really thought I went way too far on that', but the mask neutralizes the bad choices, and it enhances the weak ones. So it's just nice to be able to have that much less to worry about when I'm, playing the part.