I mean, if we go back to the original Haitian term, they'd act like slaves who've been drugged up and/or made to really believe that they are "trapped" in their own bodies, mindlessly following orders. Here's an article with some interesting journalism on zombies in Haiti in relatively recent years: https://www.harvardmagazine.com/2017/10/are-zombies-real
Pop-culture zombies though, I suppose they'd move as much and as well as they could before their muscles and bones can't physically keep up with whatever is compelling them to move.
Aunt went to a Catholic school, they made her switch. It's not just a middle ages thing