I understand that he's a superhero and superheroes are by default all big and buff.  However, there's a problem when it comes to Superman.  He gets his strength from the sun.  It's just there.  He doesn't have to lift weights or anything.

The only way to develop large muscles is to lift things that your body finds heavy.  Then to compensate, your body grows the muscles larger to compensate.  That's an oversimplification of the process, of course, but in the end it's true.  Lift heavy weights, get big muscles.

Superman, due to his yellow sun-induced strength, finds almost nothing heavy.  Unless when he's off-page Supes is out bench pressing Africa and leg pressing the moon, shouldn't he actually have a build more reminiscent of Bill Nye, the Science Guy?

My father pointed this out to me when I was in grade school and it has bothered me ever since. 

You could assume maybe Kryptonian physiology works so that the energy they get if under a yellow sun works a little like steroids. When SBPrime got a ton of energy he got more muscular right away without working out. That's just a guess. If you want a skinnier Supes though, look at Gary Franks depictions of him. I like em.

Superman also grew up on a farm doing hard labor while his powers developed.

Cause he would look lame.

Clark Kent has a red sun workout room! It all makes sense now!

I hear what you're saying.   Whose to say Supes doesn't work out or doesn't flex his muscles?  While he doesn't necessarily need to be in top physical shape, I believe given his physiology and the fact he is constantly syphoning and using energy from Earth's yellow sun, every molecule, every atom of his being is in well...Super....top notch condition, and as a result, his bone mass, and muscle mass have developed.  He's pulled the moon, he's lifted worlds.  I'd want him to have a muscular build even if according to actual "real" physiology he wouldn't have one.  Plus--and this key---who'd want a skinny Superman?  

He's constantly fighting against foes just as strong or stronger than him, which is very strenuous.

He wasn't always drawn buff. Granted that was way back in the day. I think its more for the art then the fact he's super strong, although I always wondered can he become fat? Does his Kryptonian biology keep him from getting fat under a yellow sun, because his metabolism is amped up, or if he decided to just lay about for a while and just go out as Clark would he get fat?

Superman knows that he can't rely on his powers 100% of the time.  Exposure to red-K or a red sun will sap him pretty good, so he tries to stay in good shape for those occasions when he needs to use regular fitness to get out of trouble.

well just like regular muscles I am sure hes ripped them when he lifted stuff that was heavy to him when he was young and thus his muscles got pumped and stayed buff since the yellow sun repaired them and built him stronger and stronger. Also I mean he doesnt need to eat I know he does but doesnt have too and I am sure that getting pure energy from the sun is LOW in fat so hes always lean....and a zero FAT thin person is gonna look ripped.

Uhhh, well when you think about it...

Moving a solar system with a huge chain

Moving the planet away from a threat

Fighting almost daily against Seid, Brainiac, Bizaro, Doomsday and all those big dudes..

He must build up some muscle with all that.

Beside, If he looked like a wimp it would be even far more unbelievable that he is so strong than it already is, savvy?

You're right, it doesn't make any sense.

One could say that it's the RESULT of the sunlight...

Just because you're smart doesn't mean you can't be blinded by ego or overlook things because of preconceptions about things in general or how humans behave specifically.

I believe Justice League had Martian Manhunter morph as Clark Kent and go with Lois to Superman's press conference. They were both in the same room. With that kind of stuff, it's easy to see why no one considers that.

Another point made many times is that nobody actually believes Superman has an alter ego. They just assume he's a guardian angel who's always "out there".

On the whole Clark Kent secret identity thing, read Birthright. I was really surprised how much sense it made.

The trick with Kent is that he must put up the appearance of a weakling and be unnoticeable among the people he's around. He's had to study acting books, have bad posture, and obstruct the appearance of his eyes with the glasses, even change his hair and speech patterns.

I didn't think the flight was special, I just liked that they tried to explain or at least say something about it.

He is Called Superman, just about everything he does is super, and his body was made to be super. He can easily do exhausting workouts, and not get tired because his stamina is far beyond that of human beings.

You're first saying that Superman doesn't have earth physiology, then holding him to earth's physiological standards by assuming lifting weights is the only way for him to  acquire muscle mass. He is muscular simply because he is. Some people have naturally thicker builds than others, some are skinnier by nature, some heavier. It just is what it is. Muscles equal appearance of power. Superman equals power personified. Thus Superman has big muscles.

I know i hate he buff why can't he be slender but still strong looking.

I was waiting for someone to bring this up.

Maybe Kryptonians get naturally fit at a certain age, or maybe he got all of his working out done as a boy...his powers didn't quite kick in 'till his teens, right?
 

Still man he too damn buff he like a body builder on steriods.

"@Vance Astro: not as stupid as a hero revealing there identity for publicity and then working for the government liek iron man"

He grew up on a farm where he did farm work.
From what I understand,that's pretty hard labor...and didn't his powers kick in at puberty?

The title question is a really good one, and one I have pondered for years concerning superhumans with innate superhuman strength. I never really found an answer, but right now I'd like to play the theorist.

Everyone knows Superman has an extremely dense molecular structure, but what many people don't think about is the possibility that of Supe's being a mesomorph as well. This kind of physiology combined with his solar-powered cells should allow him to develop muscle mass and tone at a superhuman rate. Most people are aware how muscles work, you work out, they split and rebuild themselves; however a lot of people don't take in the nutrition aspect of repairing cells. Your body breaks down foodstuff and uses the materials to replace and replenish preexisting cells. This fuels your body's muscles helping them to build and strengthen. Since he has a photosynthesis-like metabolism, he'd be able produce the fuel he needs to build muscles fast and spontaneously.

A mesomorph is someone with a lean build which features a lot of tone and definintion. With maturity, a man is very likely to develope a higher percentage of of muscle mass and begin to fill-out after reaching adulthood. Oftentimes muscle development can get stimulated by normal activity and although Superman is superstrong, his body still interact with itself, therefore the strenuous activity that helps supports his physique progresses from and internal stimulus instead of an external aids (such as lifting weights).

The answers could also be that Kryptonians are genetically designed to be this way, through billions of years of a ridged breeding process on their home planet.

A lot of professional athlete are mesomorphs, and although they are well built, most are not the best looking or top ten in one given muslce group or as strong as one might expect.

Ahhh... does anyone know what a PM Blast is and why I keep getting them?

"The title question is a really good one, and one I have pondered for years concerning superhumans with innate superhuman strength. I never really found an answer, but right now I'd like to play the theorist.Everyone knows Superman has an extremely dense molecular structure, but what many people don't think about is the possibility that Supe's may be a mesomorph as well. This kind of physiology combined with his solar-powered cells should allow him to develop muscle mass and tone at a superhuman rate. Most people are aware how muscles work, you work out, they split and rebuild themselves; however a lot of people don't take in the nutrition aspect of repairing cells. Your body breaks down foodstuff and uses the materials to replace and replenish preexisting cells. This fuels your body's muscles helping them to build and strengthen. A mesomorph is someone with a lean build which features a lot of tone and definintion. With maturity, a man is very likely to develope a higher percentage of of muscle mass and begin to fill-out after reaching adulthood. Oftentimes muscle development can get stimulated by normal activity and although Superman is superstrong, his body still interact with itself, therefore the strenuous activity that helps supports his physique progresses from and internal stimulus instead of an external one (such as lifting weights).The answers could also be that Kryptonians are genetically designed to be this way, through billions of years of a ridged breeding process on their home planet.A lot of professional athlete are mesomorphs, and although they are well built, most are not the best looking or top ten in one given muslce group or as strong as one might expect.Ahhh... does anyone know what a PM Blast is and why I keep getting them? "

Still i prefer a slender athletic looking Superman. Not buffed and atheltic.