“Runner’s High” is a term so ubiquitous that we all know more or less what a person’s referring to when they talk about it. Whether you’re a runner yourself or not, you’ve likely heard about runner’s high.

"Psychologically, runners may experience euphoria, a feeling of being invincible, a reduced state of discomfort or pain, and even a loss in sense of time while running," says Jesse Pittsley, Ph.D., president of the American Society for Exercise Physiologists. It’s a state that allows these athletes to not only grit their way through 26.2-mile marathons, but to kick it all into an extra gear as if physical exhaustion isn’t even a possibility. Just as interesting, runner’s high is actually something that takes over usually after a runner has started to fatigue and slow down.

Swimming, cycling, and even rowing are all other activities where the same high can take over a person’s performance — all activities that require repetition, which could be a clue to how and when runner’s high occurs. "Most research has looked at running and cycling and so forth, but when you look at some of the studies that have been done in the clinical environment, the key is being active for 30 minutes or more at a moderate intensity level to see some of these beneficial psychological outcomes,” says Cedric Bryant, Ph.D, chief science officer for the American Council on Exercise.

Researchers have recently found that the ability to get “high” while exercising is about more than just a release of endorphins and is a response that’s ingrained in our DNA. David A. Raichlen, Ph.D., an associate professor of anthropology at the University of Arizona explains that mankind’s survival was at one time dependent on the ability to chase down its food, and the reward for not giving up under physically grueling circumstances was in sustaining oneself. So feeling an actual high was an evolutionary reward, triggering whatever response was necessary for a person to catch a meal. Runner’s high was a natural painkiller used to mask pain, tired legs, heavy breathing, and sore feet in the name of survival. 

Research on the subject seems to point toward finding a sweet spot for runner’s high to kick in. You have to push yourself to get there and release the right level of endorphins. But push yourself too hard, working out to an excruciating level of pain and discomfort, and the brain won’t find that mode where the physical work becomes enjoyable again. A short and casual run won’t do it. And if you’re not conditioned well enough, running a half marathon without proper training and at too high of a pace won’t help either.

Meanwhile, endocannabinoids are another ingredient in the runner’s high recipe. It’s a naturally produced version of THC that creates the actual “high” feeling associated with runner’s high. It’s believed that endocannabinoid production is a part of the body’s reaction to stress rather than a protector from pain. Researchers say running at 70 to 85 percent of your age-adjusted maximum heart rate is optimal in spiking the primary stress hormone cortisol and producing endocannabinoids.

So it’s when all these things work together under the right circumstances for the body that athletes are able to find a whole extra level of endurance known as runner’s high