If you’re an avid runner—or cyclist, hiker or other kind of exerciser—you may have experienced “runner’s high.” It’s commonly described as a feeling of euphoria during or right after sustained moderate or high-intensity exertion that gets people hooked on exercise. The notion became popular in the 1970s, but there’s still debate over what causes it—and whether runner’s high even exists. Many exercisers never experience it, no matter how hard they work out.
Though disputed by some experts, one long-held theory is that runner’s high is due to endorphins, neurotransmitters that bind to the same cell receptors as drugs like morphine or heroin and act as natural painkillers and mood enhancers. Increased endorphins are found in the blood and spinal fluid of humans and other animals that run. And when researchers have given exercisers a drug that blocks the receptors, the euphoric effects are blocked as well. A 2008 German study provided some direct evidence that exercise-related endorphins have specific activity in areas of the brain associated with pleasure, pain, and perception of rewards.
Exercise increases levels of other neurotransmitters, too—notably dopamine, norepinephrine and serotonin, which affect mood. And then there are endocannabinoids, which have gotten increased attention in recent years as a major player in runner’s high. Yes, these are related to cannabis, better known as marijuana, and can be thought of like a natural marijuana that the body makes, since they activate the same brain centers as the drug.
A 2012 paper published in the Journal of Experimental Biology, aptly titled “Wired to Run,” looked at endocannabinoids in a small number of fit people, as well as in dogs and ferrets. The researchers took blood samples before and after a treadmill run and found that endocannabinoid levels increased in both humans and dogs afterwards—but not in the ferrets, which don’t ordinarily run. The humans also reported improved mood that correlated with increases in the chemical.
Animals that run may be motivated to do so partly because of these mood-enhancing chemicals, the authors noted. And as evolutionary biologists hypothesize, this dates back to our hunter-gatherer ancestors some two million years ago. After all, the ability of early humans to run long distances allowed them to catch prey for survival.
The runner’s high may thus have served an evolutionary advantage by helping them make this great effort, despite the extreme energy it demanded and the risk of injury.
How intense must exercise be to activate the pleasure/ reward centers in the brain? Most research suggests that high-intensity exercise is necessary, but a study in the European Journal of Applied Physiology in 2012 found that only moderate-intensity exercise boosted endocannabinoids significantly. If you’ve been sedentary—perhaps because you don’t find exercise pleasurable—there’s a catch-22, however: You must be fit enough to achieve the exercise intensity and endurance needed to get a runner’s high, yet you may not be motivated to work out so hard if you don’t get the rewards. It may take some time to get to the point where the endocannabinoids kick in, if ever.
Still, other factors may help explain runner’s high, or at least why exercise makes people feel good. Even something as simple as the rise in body temperature caused by exercise might have a calming and pleasurable effect, as can the rhythms of the activity. Keep in mind, too, that exercise involves all sorts of pleasures and rewards: It can provide a sense of control and accomplishment, for example, and serve as a distraction or time-out from daily activities and concerns.
Bottom line: Even if you don’t experience the classic runner’s high of sheer exhilaration, exercise generally produces a sense of wellbeing and can improve mood and sleep, among other benefits, over the long term—not to mention the physical payoffs. If you’re not getting any immediate pleasure from your workouts, however, you might try changing the intensity level to see if that makes a difference. Or try a different activity or location. Exercising outdoors on a beautiful day, for example, is more pleasurable than, say, running on a treadmill in a crowded windowless gym. Working out with a partner or in a group may also enhance your workout due to the added social benefit.