My guess is they maintain quickness and strength for about 30 minutes. The human blood will coagulate and rigor mortis will set in. They have to be limited by what they were before. A 90 year old zed is not going to be a powerhouse no matter how fresh.
well i would just have to say, alot of people won't move fast unless there is a drive. zombies have an obvious drive, and hunger is a big one. think of all those hungry people out there...scrapping by on not much, throw a sandwich in the mix and suddenly .....the least likely to move fast, will. we can't underestimate the undead, much less our fellow living individuals.
Rigor Mortis actually only lasts for about 24-72 hours depending upon the environmental conditions around the corpse. For example, in a dry, warm climate, rigor mortis may only last for 24 hours, but in a cold, damp climate, the effects may linger for up to three days. (I have no idea how different climates affect the body, these are random examples.
This means that while a reanimated corpse would "be slow" due to the effects of rigor mortis.
However, once the ghoul is no longer afflicted, it would be able to move freely again, at least until its muscles deteriorate to the point that it can no longer move quickly.
The exact pathology of infection has yet to be determined, as well as a concrete set of behavioral patters. Precise information is understandably diificult to attain at this stage of infection, especially for non-scientific personel. Previously acquired information has yet to be confirmed, and mixed accounts seem to bring up contradictory results. This may be due to unreliable or misinterpreted first hand accounts, or the infection may even be mutating. If the latter is the case, then tracking symptoms will be even more difficult.
I don't even want to think about the virus mutating. The one thing you can generally count on is consistent zombie behaviour. Imagine, if they begin to retain their intelligence.
I don't believe in fast Zombies. I haven't seen one. They operate on such a base level that I believe speed isn't part of their makeup. Perhaps I haven't seen one fresh enough to be fast.