I have a colleague who watches The Walking Dead and who also is a huge fan of the original (and continuing) series of graphic novels. In my many conversations with him about zombies and the show in general (we have drastically different opinions), I found it shocking that one of his main problems with the show is that it portrays Rick Grimes as having an unimaginable capacity for intense, long sustaining cardio–almost every time we see him in the earlier seasons of the show, the man is running.

You read that right.

In a show about zombies, life after the apocalypse, and the notion that the air we breathe is the cause for our post-human zombie fates, one of the most fascinating parts about the show to my colleague is how it depicts Rick Grimes’s ability to sustain intense cardio for long periods of time. At first, I couldn’t really imagine that being my reaction to the kind of show where human dismemberment seems to be a staple, but I digress. I thought about it for some time and realized that a reaction like his isn’t necessarily uncommon. Though running remains a consistent go-to for exercise, the reality is that running is far less common than it used to be thousands of years ago. You get some sense of this when you read articles about the San people in Africa, whose hunting strategies involve running after antelope for miles in order to tire them out before making the kill—called persistence hunting.

Running used to be a consistent and routine part of our human ancestors existence—humans had to run to kill prey, and they had to run in order to keep from becoming food themselves.

But this isn’t the case in the modern world—at least for a good many of us. Some eschew the act, or even the idea, of running altogether. But this means that our DNA probably still has a memory of this skill somewhere in our system waiting for the zombie apocalypse. I sought out someone with more scientific skill than I, Dr. Jim Hutchins, a Professor in the Health Sciences department at Weber State University.

He explains that, as most students of biology know, the Nervous System (our brain) can be broken down into two basic parts: the somatic and the autonomic systems. The somatic system controls the body’s voluntary actions; if you decide you want to snap your fingers, you send that command to your brain that triggers all the actions necessary to snap your fingers. The autonomic system controls your involuntary actions, or your reflexes. Breaking this down even further, the autonomic system is organized into two parts: the sympathetic and the parasympathetic. The former directs the “fight or flight” response in our organs that allows mothers to lift cars off of their children and other, less extraordinary instinctual responses. The parasympathetic controls the same organs but pushes them in a different directions, sometimes categorized as “rest and digest.”

These systems work like a finely tuned machine in order to allow us to live our lives normally. But there are situations when the biology of it all can be manipulated against us. Take the concept of “Voodoo Death.” There are recorded cases of real people dying because they had been “cursed” by someone. The belief in curses within Voodoo, or Voudou, is so potent that it can actually trigger someone’s sympathetic, autonomic response, essentially causing their body to overreact and induce a cardiac arrest or similar fatal event. The basic idea, according to Hutchins, is that when a curse triggers someone’s “fight or flight” response, they must act in order to relieve the system—the ability to flee or prepare to fight allows that system to experience catharsis, or a way to externally act on those instinctual impulses. But in the case of a curse, there is no way to physically fight it, nor can you out run it. This inability to reach any level of relief causes the person’s mind to signal overreactions to the body, overloading both the sympathetic and parasympathetic nervous systems, which can quite literally kill a person.

Effectively, Rick Grimes consistently inhabits the “fight or flight” section of his sympathetic nervous system. In the zombie apocalypse space, those individuals who survive for any length of time consistently face situations where they need to act either by running, fighting, or both. This need, and their physical ability to control those decisions, push their physical capacity for cardio to its outermost limits (i.e. mothers lifting cars off of children). The caveat here is that there must be life or death stakes. It’s the very thought of death-by-zombie which pushes Rick’s body to its limits, resulting in his incredible, borderline unbelievable, capacity for extended cardio. In fact, if he couldn’t run or fight, it’s possible his body could trigger a cardiac arrest before the zombies even caught up to him (especially if you’re dealing with Walkers instead of Runners). Couple this neurological reaction with man’s biological history of long distance, intense running back in the hunter/gatherer days, and *boom* you’ve got Rick Grimes running his heart out (almost literally).

The next time you watch The Walking Dead, keep an eye on Rick Grimes when he starts to run. Before you scoff at his Usain Bolt-like running abilities, consider the situation that forces him to run like that and wonder if you could give him a run for his money (pun intended) should you find a zombie hot on your tail.