Cap is the peak of human condition... It is above normal, but he's not juggling elephants either.
Cap is as strong as a normal human being can become, but his strength is still normal; that is to say, he does not have
superhuman strength. Thor canon established long ago that no normal human can lift Mjolnir.
A human whose strength is mechanically enhanced (Dr. Doom's armor for example,) cannot lift it; superhuman people (Thing, Colossus, Juggernaut) could not lift it because they will not pass the "worthy" test according to Odin's enchantment. Even other Asgardians cannot lift the hammer! The hammer
can be lifted or moved by a mechanical device--but not handled by a person.
I gave up reading Thor by the time I got to high school, but in my recollection the only beings (according to canon) shown to be capable of lifting Mjolnir are Odin, Thor, and Beta Ray Bill. The elves in Asgard who originally forged the hammer were able to lift it, but that was before Odin gave it the enchantment restricting its use to those he deems worthy.