Transcript:
ralston: you have super strength, right? captain: Yeah. ralston: So, why do you have to be so muscular?? wouldn't you be just as strong if you were really out of shape? Why bother? Captain: Mainly 'cause these tiny underpants only come in this size...
Muscle growth is inhibited by the hormone myostatin. Blocking the gene that produces myostatin results in stronger, more muscular animals and people. Superman may have the Kryptonian equivalent blocked.