Zombie physics has never quite been perfected.
Its either one of two ways...
A Zombie is a human with a virus that manifests itself after death and these types are are some animalistic motherfuckers that run and jump and shit.
OR
A Zombie is a dead human, bought forth by some mystical force (Apololypse, or just because, etc.) and they tend to slow prodding motherfuckers that herd.
The Walking Dead can't seem to figure out which one is better, so they have traits of them all and are manipulated depending on what dumb drama they want to create.