I'd say no differently mobile than an ordinary human if maybe a bit slower to account for decay/rigor mortis
. Slow shuffling zombies creates too many questions and problems when it comes to the action in a movie. Namely on how something slow moving can be so hard to escape from and overcome?! But I even more hate a modern trend to make zombies movie very, very rapidly almost having super-human levels of speed, strength and agility which makes even LESS sense.