As if you needed a reason to believe that zombies should be depicted as lumbering reanimated corpses rather than ridiculous sprinting wraiths, there's now scientific support for that.
Neuroscientists Timothy Verstynen and Bradley Voytek have written Do Zombies Dream of Undead Sheep?: A Neuroscientific View of the Zombie Brain, which shows "how zombism can be understood in terms of current knowledge regarding how the brain works." The book includes chapters like "Hungry, Angry and Stupid is No Way to Go Through Unlife," "There's No Crying in the Zombie Apocalypse!" and ... "The Neural Correlates of Lumbering."
Slate.com has an excerpt that breezily dissects zombie behavior to arrive at the nature of their dysfunction; it's fascinating, if not easily quoted in small chunks: "... we argue that the cluster of symptoms seen in zombies, the wide stance, lumbering walk, lack of freezing, ease in general planning and execution of actions, reflects a pattern of cerebellar degeneration. That is, cerebellar dysfunction would lead to many of the motor symptoms of the zombie infection. However, cortical motor areas and basal ganglia pathways should be relatively intact."
But what about those fast-moving zombies? OK, fine: Verstynen and Voytek have an answer for them, too (just don't share it with Resident Evil fans or you'll never win the argument).