You may have thought endurance runners who talked about that hitting a high were crazy, but they're not. The feeling of exhilaration that makes the running feel so easy and fun is real. And now, new research shows that it evolved to help us survive as hunter-gatherers, Gizmodo reported.

The study, published in the Journal of Experimental Biology, found that the runner's high is a result of the brain releasing neurotransmitters called endocannabinoids that activate cannabinoid recepters in brain reward regions.

Researchers tested the amount of circulating (in blood) endocannabinoids in different animals — those that evolved to participate in regular endurance exercise and those that didn't — before and after they ran on a treadmill for 30 minutes. Humans and dogs (endurance exercisers) saw a significant increase in the high-inducing neurotransmitters. Ferrets (sedentary), on the other hand, did not show an increase.

This research shows that the runner's high likely evolved to help our hunter-gatherer ancestors run long distances in order to find food. Those who didn't experience the high may not have been able to last and find adequate food. While we may not run to find food anymore, the runner's high can explain why people, despite the pain, lace up those running shoes over and over again.