Of the many benefits from exercise, which include cardiovascular strengthening, the production of new brain cells, and overall improvement in brain performance, the classic 'Runner's High' can be included in this list, too.

This euphoric feeling has been attributed to a rush of endorphins released during exercise. These endorphins, which are our bodies natural pain killers, help prevent muscles from feeling pain. However, according to a new study that looked at exercise on treadmills,  the results found it is unlikely that endorphins in the blood contribute to a euphoric feeling, or any mood change at all. In fact, the research showed that endorphins do not pass the blood-brain barrier, meaning endorphins cannot be the source of our altered mental states that some of us feel when we run long distances.

Endocannabinoids

That relaxed post-run feeling may instead be due to endocannabinoids — biochemical substances similar to cannabis but naturally produced by the body. According to the study, exercise increases the levels of endocannabinoids in the bloodstream. And, unlike endorphins, endocannabinoids can move easily through the cellular barrier separating the bloodstream from the brain, where these mood-improving neuromodulators promote short-term psychoactive effects, such as reduced anxiety and feelings of calm.

The current study was built off of previous ones that tested this theory. In one study, researchers coaxed dogs, people and ferrets to run on treadmills, while measuring their blood levels of endocannabinoids. The subjects were chosen because dogs and humans are designed for distance running. Ferrets are not. They are sprinters and did not produce extra cannabinoids while treadmill running. The dogs and people did, though, indicating that they most likely were experiencing a runner’s high and it could be traced to their internal cannabinoids.

A 2015 study used mice, who are eager runners. Researchers chemically blocked endorphins to the brain and then did the same with endocannabinoids. When their endocannabinoid system was turned off, the animals finished their runs just as anxious and twitchy as they had been at the start, suggesting that they had felt no runner’s high. But when their endorphins were blocked, their behavior after running was calmer, relatively more blissed-out. They seemed to have developed that familiar, mild buzz, even though their endorphin systems had been inactivated.

The latest study used human beings this time. 63 experienced runners, male and female, were  randomly assigned to receive naloxone, a drug that blocks the uptake of endorphins, and the rest, a placebo. The volunteers then ran for 45 minutes and, on another day, walked for the same amount of time. After each session, the scientists drew blood and repeated the psychological tests. They also asked the volunteers whether they thought they had experienced a runner’s high.

Most said yes, they had felt buzzed during the run, but not the walk, with no differences between the naloxone and placebo groups. All showed increases, too, in their blood levels of endocannabinoids after running and equivalent changes in their emotional states. Their euphoria after running was greater and their anxiety less, even if their endorphin system had been turned off.

Why do have a runner's high in the first place? No one really knows for sure, but some scientists believe it harkens back to prehistoric days when we had to spend a lot of time running after our food. To keep us going and feeling good about it, the body found a way to keep it "euphoric" while also keeping it sustained.

Here's wishing your next run to be healthful and blissful.