The Crimson Binome
Hero
He's pushing the peak of human abilities by a considerable margin, but he's still acting within the bounds of what some people might believe a nonmagical human could do. The Marvel-verse has alternate physics in that it allows for regular humans to do things that people in the real world can't do. The Kingpin is another example of a mundane human whose physique would be impossible in our real world.Superhuman? More like the peak of human physical ability.
Their alternative physics (at least as long as you don't get into superpowers at all) is still close enough to our real world physics that the reader is willing to buy into it. If we see Captain America perform a twenty-foot standing long jump or lift a thousand pounds over his head, then most readers are just going to think that's really impressive rather than immediately jumping to the conclusion that it should be impossible. To contrast, if we see him perform a twenty-foot standing high jump, or lift five thousand pounds over his head, then everyone immediately knows that there's something wrong with this story because those feats blow our suspension of disbelief out of the water.
I think there are places where they refer to those heightened-but-believable constraints as "cinematic reality", and that's where most people want their fighters to live (as opposed to "mythic reality", where a sufficiently powerful fighter can balance on clouds and juggle elephants).