Have you ever watched a group of exhausted runners limp across a marathon finish line and thought: Why would anyone ever do that voluntarily? Maybe it's the runner's high.
Ask a runner to explain themselves, and chances are they'll say something about the fabled runner's high. But what, exactly, is a runner's high? How does it affect your body, and can it really make you feel intoxicated?
What is a runner's high?
You've just finished a hard run. Your legs are heavy and sore, heart pounding, clothes sticking to your sweaty back. And you're smiling, because you feel utterly at peace with the world.
This is the runner's high — the strange euphoria that sets in after a long bout of aerobic exercise.
The term "runner's high" probably originated sometime in the 1970s during the United States' first recreational running boom, according to reporting by the Chicago Tribune (opens in new tab). "In the scientific literature, it's used as more of a shorthand for a range of changes to your physiological state that occur with exercise," David Raichlen, an evolutionary biologist at the University of Southern California, told Live Science.
That range of changes includes subjective things like improved mood and a general sense of well-being, as well as measurable alterations in body chemistry. Over the last few decades, one particular group of exercise-related chemicals has received a lot of scientific attention for its link to a runner's high: endorphins.
How are endorphins related to a runner's high?
As the character Elle Woods famously remarked in 2001's "Legally Blonde," "Exercise gives you endorphins. Endorphins make you happy. Happy people just don't shoot their husbands."
It's certainly true that exercise gives you endorphins. During aerobic exercise, your body begins to release a cocktail of chemicals, including several different endorphins. Functionally, these compounds mimic the effects of opioids, like morphine, but on a much milder scale. Studies show that they help to relax your body and decrease your perception of pain, according to a 2010 review paper published in the Hawaii Medical Journal (opens in new tab).
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For decades, many scientists believed that in addition to relieving pain, endorphins also boosted a tired runner's mood. There was just one problem: Endorphins don't cross the blood-brain barrier, meaning that they shouldn't be directly linked to happiness.
When scientists began to take a closer look at the chemicals coursing through runners' bodies, they found intriguing results. They found a whole slew of lipid chemicals, called endocannabinoids, and neurotransmitters that hadn't previously been associated with exercise percolating in various tissues. Like endorphins, endocannabinoids can influence mood. But unlike endorphins, these chemicals can cross the blood-brain barrier. Despite Elle Woods' claim, it appears that endorphins aren't solely responsible for the runner's high.(opens in new tab)
How does a runner's high affect your body and mind?
New research suggests that endocannabinoids are actually the key to unlocking that feeling of inner peace. As their name suggests, endocannabinoids (opens in new tab) are chemically related to the active ingredient in cannabis, tetrahydrocannabinol, or THC.
Like THC, endocannabinoids — especially one called anandamide — can cross the blood-brain barrier and bind to receptors on your neurons. However, unlike THC, which "just kind of piggybacks on our body's own systems," Raichlen said, endocannabinoids are produced naturally within your body and tend to have more subtle effects on your mental state. "That's why it feels quite different." A runner's high is less of a high and more of a gentle lift.
In addition to endorphins and endocannabinoids, exercise also releases the "feel-good" chemical dopamine, a heavy-hitter for your body's reward system, according to the National Institute on Drug Abuse. This pleasure inducing neurotransmitter is also released when you win the lottery, orgasm or take a bite of an ice cream sundae. Dopamine might contribute to the overall sensation to the runner's high as well, providing your body with a little mood boost for its hard work, according to research published in 2016 in the journal Frontiers in Psychology.
How can you get a runner's high?
The most obvious way to get a runner's high is to start running, particularly long-distance running. It may take several miles for the effects to kick in, though it's difficult to quantify exactly when, where and for how long a runner's high will occur, Gina Kolata reported for the New York Times (opens in new tab). And not every runner — or every run — will be able to produce a runner's high, according to David Linden, a professor of neuroscience at Johns Hopkins University, wrote on the Hopkins health site (opens in new tab). This variability has led some snarky Twitter users to conclude that the runner's high is, in fact, a myth, despite the physiological changes associated with it.
Other aerobic activities, including biking, swimming and strenuous hiking, can trigger the same response without necessarily forcing you to pound the pavement.
Interestingly, humans aren't the only animals that have exhibited signs of runner's high. Several experiments have observed a similar phenomenon in mice. Raichlen's lab has also tested dogs and ferrets by sticking them on a treadmill and looking for exercise-induced euphoria, according to research published in the Journal of Experimental Biology (opens in new tab). After 30 minutes of running, the dogs appeared at-ease; blood tests revealed elevated levels of endocannabinoids in their systems. "We didn't see that in the ferrets," Raichlen said.
Is a runner's high good for you?
One major benefit to achieving a runner's high is that it makes exercise more enjoyable. By extension, this makes people more likely to stick to an exercise routine, which, according to the American Heart Association (opens in new tab), is a key component of long-term heart health. There is also good evidence that, over the long term, exercise can have significant mental health benefits such as reducing anxiety and stress, according to research published in 2006 in the Primary Care Companion to The Journal of Clinical Psychiatry (opens in new tab).
So far, there is little evidence that a runner's high is healthy in and of itself. But at the very least, Raichlen said, "It's not unhealthy." So go ahead and lace up your shoes. You're free to chase that runner's high as far as it takes you.
Originally published on Live Science.