Getting high from marathons

Cannabis-like chemicals may be the cause of the so-called "runners' high" experienced by athletes, new research has revealed this week.

Traditionally, a surge of endorphines, the body's own morphine-like chemicals, triggered by exercise were thought to account for the sense of calm elation experienced by runners.

Instead, a paper published this week inPNASshows thatcannabinoids, nerve chemicals that act on the same parts of the brain that are sensitive to the effects of cannabis, are the cause.

Unlike endorphins, which cannot cross over into the brain from the bloodstream, cannabinoids are able to move between the two. And so even though running and exercise do lead to the release of endorphins around the body, they cannot penetrate the brain.

To investigate these effects, researchers from the University of Heidelberg worked with mice, which also appear to experience a runners' high. Given wheels in their cages, the mice chose to run up to six or seven kilometres a day.

After letting the mice run for five hours, Johannes Fuss and his team studied their behaviour.

"We found that both the pain and the anxiety were reduced after running," he said.

Meanwhile, he also found that the levels of endocannabinoids in the blood had risen.

By blocking the receptors for both endorphins and cannabinoids, they were able to see how these chemicals affected the behaviour of the mice.

It was only if their cannabinoid receptors were blocked that the mice did not have reduced pain and anxiety. If their endorphin receptors were blocked, the mice still got their runners' high.

As well as reduced pain and anxiety, runners' high also gives people feelings of euphoria and relaxation. Although these can't be measured in mice, Fuss is confident that "the same mechanism in humans" is occurring.

That said, some people just don't get that samr buzz from running. This could be because their bodies don't produce cannabinoids when they run, or that their bodies respond to them in a different way...