If a girl was flirtingly fingering the outline of a guy's 6 pack in medieval times how would you describe it? I doubt his abs would have been called 6 packs a few hundred years back... Would "abs" do it?
You might want to describe it more literally. She could be stroking his taut muscles, the ridges of his abdomen, something that brings up imagery, but isn't connected to any modern day exercise buzzwords. It might actually be just as anachronistic, but it won't connect people to modern day concepts as much, maybe.
I could see her tracing the contours of his muscles and admiring the way they matched those beaten into his armour. Kinky
