As runners, we all know there’s no better feeling than the runner’s high — that mood-lifting, exhilarating sensation that occurs only after a hard run that seems like your brain’s way of rewarding you for a good effort. While there’s no doubt that this feeling is real, the reason behind it is less certain. For years, scientists have pointed toward endorphins as the main cause of the runner’s high, but more recent research has suggested this may not be the case. Instead, some researchers believe it could be linked to our ancient biology, and a class of chemicals called endocannabinoids may be the real reason running makes us so happy.
Running — it’s in our DNA
In a paper titled Endurance running and the evolution of Homo, biologist Dennis Bramble and paleoanthropologist Daniel Lieberman hypothesized that our ability to experience the runner’s high is linked to the lives of our earliest ancestors. More specifically, Bramble and Lieberman suggested that the feel-good chemicals released in early humans’ brains originally served as a reward to motivate them to continue hunting and gathering.
This would have been very important for the survival of early humans because traveling all day for the purpose of finding or capturing food required large amounts of energy, which is a caloric risk when there’s no guarantee that your efforts will be rewarded. For this reason, early humans (and today’s humans, for that matter) were more predisposed to conserving energy and so needed some other form of motivation to exert themselves physically. It is possible, then, that early humans got ‘high’ from running to prevent them from starving.
The runner’s high: will the real culprit please stand up?
David Raichlen is an anthropologist at the University of Southern California and a recreational runner. He believes that this reward for hard work in humans’ brains would have to both relieve pain and cause pleasure, or else it wouldn’t be enough to motivate them to keep going. While most of the research points toward the post-exercise endorphin rush as the cause of this, he thinks another class of chemicals called endocannabinoids are more likely the culprit.
Yes, endocannabinoids are the same chemicals that are mimicked by cannabis, which both alleviate pain and improve your mood. In fact, brain scientists often refer to endocannabinoids as the “don’t worry, be happy” chemical. Recent research has revealed that these compounds, instead of endorphins, are more likely the cause of the runner’s high because of their size. Endorphins are released into your bloodstream during exercise, but they’re too large to cross the blood-brain barrier, so they can’t cross over into your brain. Endocannabinoids, on the other hand, are small enough to cross over and act on specific receptors in your brain.
To test his theory, Raichlen put regular runners on a treadmill at varying intensities and measured the endocannabinoid levels in their blood both before and after. He found that walking slowly for 30 minutes had very little effect, and neither did running at maximum intensity. When participants ran at a moderate pace, their endocannabinoid levels tripled — and they felt really good afterward. He speculates that this moderate intensity would have been similar to the effort put forth by our ancient ancestors when they were hunting and gathering.
What does this mean for runners?
This endocannabinoid high can be achieved not just through running, but also cycling, walking on an incline and hiking. In truth, the ‘runner’s high’ is not really caused by running, but by persistence. All you have to do is exercise at a moderate intensity for at least 20 minutes to unlock the mood-boosting benefits.
And guess what? The endocannabinoid high also helps us connect with others, which is why you feel particularly good after running with a friend or group. This good feeling carries through the rest of your day, and studies have suggested that when people exercise they have more positive interactions with others around them.
Finally, as you exercise more, your brain actually increases its density of endocannabinoid binding sites, which makes your high even better. The more regularly you run, the more you get rewarded for it. So the next time you’re struggling with motivation to go out for your run, perhaps chasing that high will be enough incentive to get you out the door.