CAN HUMANS OUTRUN HORSES?

But these weren’t ordinary runners—Teeny was racing against horses, a journey detailed in ESPN’s new four-episode GIRL v. HORSE podcast series.

For the 35-year-old, this race marked the pinnacle of a five-year journey to accomplish something seemingly impossible: race a horse and win. As she approached the finish line, “my body was on autopilot,” she says. “I knew that if I stopped, it would be difficult to keep going.” But she did keep going. She kept pushing, and when she crossed that fifty-mile mark, she had done it. She beat a horse.

While Teeny isn’t the first person to outrun a horse (Welsh marathoner Huw Lobb holds that title), her achievement was anything but guaranteed. Teeny had grown up running, but five years prior, she was diagnosed with epilepsy. This condition had sidelined her running career as she struggled to find the proper medication to control her seizures. For Teeny, this race wasn’t just about endurance—it was about reclaiming control over her body and testing the limits of her physical and mental strength.

But, still, how is it that Teeny, or any human, has ever stood a chance against a horse?

Why humans are built for long-distance running

Teeny’s quest to outrun a horse began after her epilepsy diagnosis. She stumbled upon a chapter in Born to Run that introduced her to the endurance running hypothesis. This theory, popularized by Harvard paleoanthropologist David Lieberman, suggests that humans evolved to run long distances thanks to adaptations like short toes, long legs, and upright posture.

“Almost every system in the body is adapted to help us run,” Lieberman says. He adds that our cardiovascular systems are uniquely efficient at delivering oxygen to muscles, especially compared to other primates. And maybe most importantly, humans are better than most animals at shedding heat, due to our unique ability to sweat, Lieberman says.

The hypothesis posits that we developed these traits, at least partly because our hominid ancestors practiced persistence hunting—chasing prey until it was too exhausted to continue.  An antelope could easily outrun a human over short distances, but the tables turn over long distances, Lieberman says.

Running might also have had something to do with how our brains evolved. David Raichlen, a professor of biological sciences at the University of South Carolina, says that running can make us better at cognitive tasks, improve cognition, relieve anxiety, and even protect us from neurodegenerative diseases. “From an evolutionary perspective, it makes sense,” Raichlen says. “In a more naturalistic setting, oftentimes we’re trying to find food and that requires a combination of being physically active and using your brain.”

Running also causes our brains to release opioids and endocannabinoids, which are likely what contributes to the so-called “runner’s high.” These chemicals might have made it more appealing for our hominid ancestors to expend energy and could be a big part of our motivation to run and push past pain, Raichlen says.

Not everyone buys into the endurance running hypothesis, though. Running expends much more energy than walking, and only a handful of modern-day societies still practice endurance hunting.(Walking is the sixth vital sign. Here’s how to do it right.)

“We can say that humans are meant for endurance exercise,” says Alexandra Coates, a postdoctoral fellow at Simon Fraser University and triathlete. She adds, however, that walking is more efficient than running, and that we likely evolved to walk for long distances, not run.

Nicholas Tiller, a research associate at Lundquist Institute, Harbor-UCLA Medical Center, also doubts that we evolved to run ultramarathon distances, mainly because of their potentially negative impacts on our health. Although all forms of exercise have a net benefit, extreme exercise, like ultramarathons, involves pushing our bodies to the limit.

Studies show that ultramarathon running could potentially cause harm to organ systems, including the cardiovascular system, skeletal muscles, and kidneys. “I still contest that our bodies evolved to withstand the rigor of an ultra-endurance event,” Tiller says. 

Still, Lieberman maintains that running played some role in our evolution. Just this year, the endurance running hypothesis got some support from a study that used AI to comb through historical records to find reports of persistence hunting. The researchers found 400 separate ethnographic cases of endurance pursuit-like hunting from around the world, an order of magnitude more than had previously been recorded. So, while some researchers remain skeptical, Lieberman says that running “was part of the mix.”

Regardless of whether we evolved specifically to run, outrunning a horse is a more difficult challenge than persistence hunting. While most species aren’t adapted for long-distance running, Coates says horses are some of the best endurance runners in the animal kingdom. Outrunning one is a testament to human endurance—and requires lots and lots of training.

Luckily, our bodies are well-adapted to make us better endurance runners. Once a person starts endurance-based training, Coates says, their body starts making changes that increase their VO2 max, or the maximum rate at which their body can use oxygen. That means that the number of mitochondria in their cells will grow.

(Here’s why boosting your VO2 max could help you live longer.)

Capillaries will start sprouting in their heart and muscles to shuttle oxygen to their cells. They’ll also develop more slow oxidative fibers, which contract slowly and use aerobic respiration more efficiently than other types of muscle. Over time, their heart size will increase, and their body composition will change to support more muscle.

Indeed, studies suggest that ultra-running is often associated with a psychological drive to test one’s limits. Motivation and goal-setting are key components of getting through a race for most ultramarathoners. In addition, research shows that internal states significantly impact race performance: self-belief and positive self-talk are important factors in getting through a race.

“It takes a certain amount of harnessing your mind in addition to your body,” Teeny says.