I have a new found love for the Zombie style of movies. I have always enjoyed them, even as a youngster. With my uncle as director & principle photographer we even made our own remake of the Romero classic Night of the Living Dead. It was 1987, and I was in the 8th grade. I played the the original cemetery Zombie. The other reason is my wife has a case of "zombie love". She is all about anything zombie. Even the desktop on the laptop is zombie pinup girl. As any gentleman out there knows, if your wife is all about something, then somehow you tend to be directed in that direction.
The fast moving zombies are my preferred type because, scientifically it makes a lot more sense to me. I am not a geneticist, a cellular biologist, medical examiner or any other type of medical expert that makes my opinion the correct one. Although the current trend of the zombie genre leaning towards the fast movers has made me enjoy the movies all the more.
The process that makes a person a zombie is spread in the same way that a blood born pathogen is spread. Contact with infected bodily fluids (usually through a bite) will turn a normal human into a zombie. Most the time it is the work of some secret agency's scientist whose work was meant for good, but the government has taken the research for there own diabolical purpose. If you think about it, if the zombie bites you, you are infected. That is the way that a lot of pathogens are spread in the real world. Rabies is a good example of a disease spreading in this manner.
Since the pathogen has the ability to bring dead things back to life, why wouldn't it continue the stimulation of the cells? That would explain the need that the undead have for continuous intake of calories. In this case it would be other people, especially their brains. I have wondered many times though, why don't more of the zombies eat each other? Can they sense which creatures are already infected? Does it really matter? I mean it's not like they are going to die from it.
If the pathogen has jump started the metabolic rate at which the cells consume food, I would think that you would have somewhat of a "burn out" factor. As soon as the amount of food decreases then the cells will die. Even in zombie land you have to have some sort of energy to keep the machine working. If we look at it from a normal human point of view, an example would be amphetamines. They cause the body to have more energy, although its cause is chemical, but you still burn the calories. They will suppress the appetite, so you don't eat. That partly explains why you don't encounter very many obese crack heads. If the pathogen caused the metabolic jump without the appetite suppression, you would have a being with an overabundance of energy and the need to refuel the body to keep it going at that rate.
Movies go both ways with another point. Sometimes the pathogen will only animate the recently dead cells. Think of it like a a version of CPR from hell. I personally believe that this would be the correct way that it would happen, based on what we know about the rejuvenation of damaged cells. Cryogenics is one example. After the cell has lacked the "spark of life" for a certain period time, the cell can't be reanimated again. Think of that car you had in college. There is a point where nothing can be done. No Ford Escort zombies so to speak.
If you happen to subscribe to the slow zombie theory, this is where it would come into play. As opposed to the hospital morgue type zombies or freshly bitten types, the ones that have been in the ground for quite a while would be slow. As the body decomposes, you would lose mobility. The lack of synovial fluid in your joints would give you the jerky style movements. As the softer tissue is gone you just won't be winning any marathons.
I reside on the other side of the fence on this one. Only the recently (hours) dead and newly bitten would be reanimated. The pathogen makes them human versions of a natural predator. This would make two types of zombies. The ones that were living humans would get the greater benefits from the pathogen. Faster movements, better sense of smell, better hearing etc. The actual corpse zombies would get some of the benefits but they are starting from a different level.
This is all well and good, but we all know that in the movies the zombies don't really need all the enhanced speed and stalking skills. Anyone can track down that one girl that is a firm believer in the philosophy that screaming at a high volume for long periods of time is the way to solve any situation. Don't feel guilty, we are all glad to see her become zombie lunch.