well i think not to fast or slow just sprintish more like and do they get tired and the virus could possibly make stronger some of there appendages who really knows guess if there ever really is an outbreak we will know
They're brains being dead, and probably at least a little damaged, they should have very poor motor skills. That is also the reason why animal zombies aren't all that terrifying. If a human zombie has trouble coordinating two legs, then how could an animal zombie handle four or wings.
Well, I think this all depends on what kind of zombies you're talking about, and if we're talking about a viral zombie outbreak, we also need to break down what the effects of the virus are on a physiological basis.
For example, if ebola ever turns into an aggressive pseudo zombie plague, I don't see the victims being very fast when approaching the 'crash and bleed-out' phase of infection - due to their organs and body tissue practically liquefying at an alarming rate. The spraying out and bowel emptying that ensues is a different story however. With that level of spewing & spraying of 'hot fluid' (as in bio-hazard) that occurs, they needn't be that fast... All they'd need (as they're driven by the virus' need to multiply) is a properly populated area, such as a mall, or even a hospital room. Btw, ebola DOES behave in this manner...
Now if we're talking about your usual 'rise from the dead' variety of zombie... I think it well depends on the freshness of the corpse.
If it's a relatively fresh corpse, I'd say it would be reasonable to assume that these zombies can be quick. Deteriorating over time, as flesh and tendons tighten up, etc.
Once the zombie reaches a certain level of necrosis, then they'd become more of the shuffling stifflegged variety of zombie that we're most used to seeing - but the draw back to this, is that because their muscles have become more rigid and tighter, it will also result in them being 'stronger' as well...
If you've ever had an arm cramp where your muscles act on their own and the contractions give you a 'death grip', or even a severely cramped leg, then you get an idea of just how strong the muscles can squeeze and pull in on themselves in this manner.
Zombies are undead. Meaning they follow all the stages of human decomposition. After rigor mortis sets in, zombies are going to be moving very fast at all. Also, from what I understand, the elements can cause a body to rot much, much faster. So in theory, a zombie in a casket will rot slower then a zombie enduring the heat, humidity, rain, and possible lightning strike....