When I hear complaints about superhero comics, one of the most common issues people have with the genre is that "it's just a bunch of muscleheads beating on each other?" and further, others will say "Why don't they look like normal people? They're like Adonis with their absolutely perfect body and all."
Well, to me it actually makes sense on several different levels.

• Activity level: These guys spend 8-to-10 hours a day being very active. They are running around and jumping. They are also fighting a lot too. None of these are exactly what you'd call a sedentary activity. That burns calories. That makes a person have a nice body.
• Feel the power: A lot of heroes also have a power that is fueled by something inside their own body. Whether it's super-strength, laser blasts from their hands or pulling water molecules from the air to create ice. These powers have to be generated by something. If these guys aren't pulling their energy source from another dimension or the sun's yellow radiation they have to be creating it someplace, somehow. And if you think about it, they must have the world's best fuel-to-output ratio in the universe with some of the things their powers let them do. They eat a hot dog and can toss a pickup truck like its a Frisbee.
• I want to look nice: Some superheroes have the ability to transform themselves in one fashion or another, so why shouldn't they transform themselves into the perfect image of humanity?
• Custom built: Other heroes are actually guys who wear body armor — whether it be the bulky Iron Man kind or a skin-tight suit. So with that in mind, why wouldn't they make the armor in a way that squeezes them into the Hercules look?
• They drew me this way: And finally, the true reason why superheros look so nice: Because they were drawn that way. Really, a lot of comic artists are great a drawing an unclothed figure that's anatomically perfect. Wrinkles and seams are kind of tough to do, so a skin-tight suit is a great option, especially when each superhero is color-coded for easy identification.

Got your own ideas about the perfect superhero body? Let me know in the comments!