Runners describe it as a feeling of euphoria: when the pain fades away and all that's left is a sense of floating on air. It's called a runner's high, and a new study has found that it might be pretty similar to that other kind of high.

German researchers recently published a study in the Proceedings of the National Academy of Sciences that shows that it's not endorphins that give runners that lovely "I can conquer the world" feeling when they are working out. Rather, it's a a by-product of the body's endocannabinoid system that affects the brain much like marijuana.

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Researchers describe endocannabinoids as the body's own version of marijuana. Unlike endorphins, endocannabinoids — such as anandamide — can pass through the blood-brain barrier just like cannabis does. There, they can affect several brain processes from appetite to mood to the perception of pain. Just like cannabis.

For the study, researchers tracked the anxiety levels and pain tolerance of mice before and after running on a wheel. A normal run diminished anxiety and increased the amount of pain the mice could tolerate. But when researchers blocked the mice's production of anandamide, they found that the mice were as anxious after their runs as before, and more sensitive to pain. When they blocked the production of endorphins but left the endocannabinoid system alone, the runner's high returned.

"We thus show for the first time to our knowledge that cannabinoid receptors are crucial for main aspects of a runner’s high," the researchers wrote.

Of course, this study was conducted on mice running on a wheel and not humans running on a treadmill. So it's not clear if the results will translate from one mammal to the next. But if you're a runner, or aspire to be one, it's yet another perk to consider the next time you're cruising along — feeling that free and completely legal high.

Is a runner's high similar to a marijuana high?
There could be a good reason runners are in such great mood after their workouts.