Ha ha. It's true. I watched "Superman" with the Richard Donner commentary (which was excellent, BTW- lots of good stories) and it turns out Christopher Reeve gained 40 pounds of muscle to play Supes. He was trained by none other than David Prowse, the muscular actor who played Vader himself, as well as Julian, the writer's bodyguard, from "A Clockwork Orange."
I found the commentary great. It is really interesting to hear how the effects were done the old fashioned way through inventiveness and camera work rather than the boring old "this was done with CGI."