Well, his usual stats are 6'3" and 235lbs, so that's super-heavyweight in boxing (until they renamed it 'Unlimited' weight class) and he's a wall of a man. It's hard to relate. Also slightly impractical, as such a physique can have flexibility issues --- unless of course, Superman's unique alien physiology allows him, as a Kryptonian, to have yogic flexibility in his joints, tendons and sinews as well as huge muscles.
At this rate of analysis it becomes faintly ridiculous, to be honest. Some guy can fire off fists as fast as bullets, with the punching power and impact force to match, and next thing you know....they just bounce off Superman cos' bullets bounce off Superman. For the longest time I did not like the character at all, and this sort of thread reminds me why.
I'm glad I realized long ago that muscles and mass have little or nothing to do with super-strength, the only caveat being you should be reasonably fit and able-bodied to facilitate the abolition of imaginary limitations. Training martial arts will do it. So I guess I don't care how Superman is drawn. Lean and mean, or big n' bulky.