A runner's body prefers to go at a certain pace regardless of distance

It makes perfect sense that a runner will go faster if they’re running a shorter distance and slower when they’re running farther. After all, a sprinter who’s going all-out for just 100 or 400 meters flies when compared to a marathon runner setting off on a journey of 26.2 miles (42.2 km).

But does the pattern hold when a runner isn’t taking part in a race?

According to a study published Thursday in the peer-reviewed journal Current Biology, the human body has a natural tendency to run at a speed that reduces the number of calories it consumes — regardless of distance.

“Across all run distances, runners varied their average preferred speeds by [roughly 5.5 percent], with no clear trend across run distance,” the researchers write. They analyzed runs between 0.6 and 28 miles (1-45 km).

It goes back to evolution

Running burns a lot of energy. Most animals burn more calories running than they do swimming, flying, or walking. While humans are good runners in many ways, they aren’t particularly efficient. According to some estimates, humans have to invest twice as much energy per mile as many human-sized animals. For a long time, researchers thought humans burned the same amount of energy per mile no matter how fast they ran. But over the last decade or so, researchers who brought runners into the lab have been developing a new idea. Maybe there’s an optimal speed at which humans run at peak efficiency. And even more intriguingly, maybe humans know — implicitly — what that speed is.

Researchers made as much progress as they could toward answering those questions by studying runners in the lab. For this new study, they turned to a relatively new source of data: fitness trackers. “We were able to fuse the two datasets to gain new insights and combine the more messy wearable data with the gold standard lab experiments to learn about how people run out in the world,” says biomechanical engineer Jennifer Hicks, a co-author of the new study.

No matter the (short) distance, a runner goes at the same pace

The researchers analyzed more than 28,000 hours worth of non-racing runs by more than 4,500 Lumo Bodytech fitness tracker users. Their dataset contained information on nearly 40,000 separate runs. To figure out if runners changed their speed depending on distance, the researchers focused on runners who’d logged 2-, 4, and 6-mile runs, give or take half a mile (3.22, 6.44, and 9.66 ± 0.80 km). That group included roughly 400 runners. Then the researchers looked at the pace at which each of those runners ran. “We found no differences in runners’ speeds across this 3-fold change in run distance,” they wrote. They repeated the same type of analysis for similar intervals and found similar results.

Of course, there are times when a runner wants to pick up the pace and exceed their evolutionary default settings. The researchers point to other ways for a runner to maximize their speed. “Listening to music with a faster pace has been shown to help speed up stride frequency, which can then increase running speed,” says neuromechanics researcher Jessica Selinger, a co-author of the study. Running with others can do the trick, too. And if you’re taking part in a race rather than listening to what your body wants, that’s a totally different story.