Alternate title: Why does Superman have big muscles?
I've long wondered about this. You get big muscles by lifting big weights many, many times. In his normal life, nothing represents a heavy weight for Supes, so he'd have to put in the hours in a gym, like other musceley fellows. But where is this gym? On Jupiter? It couldn't be on Earth, or we'd be aware of the gravitational attraction of the plates.
What are the weights made of? What kind of bench could support him and the bar he'd be using for presses or the dumbbells he'd be using for flyes?
And look at those lats! Man, you could fly with those things! Oh, wait, he does. Anyway, I'd like to see the pulldown machine he uses to get those lats.
I suppose that the heavy-duty musculature of superheroes is the outward manifestation of their superheroness, rather than something they all coincidentally happen to work to get. The rest of us have to sweat and strain for muscular development, but those darned superheroes just have it because they're superheroes.
Superheroines don't tend to be extremely muscular, in comics or on the screen, but they do tend to be beautiful and sexy. (Lynda Carter says that Eliza Dushku should be Wonder Woman, and who in his right mind would argue with that, or with any reason to see Dushku on the big screen? In a bikini?) So I assume that their beauty and sexiness is the outward manifestation of their superheroineness.
All of this might well make the rest of us feel inferior. Positively mortal!