It doesn't matter if it's muscle when the end result is that he still can't breathe! He may care about Bucky a great deal, but lines have to be drawn. He will deal with the bruising bites, but he will not suffer any unfortunate crushing accidents underneath him.

Besides, now that he's not vaguely worried about being able to move, there's a soft moan of approval when lips move back to his neck, followed by his hands sliding up and over Bucky's sides, along his back.

"Much better, James," he practically purrs.