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A recent study has shown that runner’s high is not caused by endorphins, but by compounds which are also released when smoking marijuana.
Research was conducted on laboratory mice, by a group of experts at the Central Institute of Mental Health at the University of Heidelberg, in Mannheim, Germany. The results were published this week in Proceedings of the National Academy of Sciences.
Previously it had been theorized that the feeling of exhilaration and relaxation following an intense work-out is caused by endorphins, or “happy hormones”.
Prior research had found higher levels of these compounds following vigorous exercise, and experts believed that these substances which act as natural pain relievers also contributed to feelings of well-being and pleasure.
The theory however soon collapsed like a house of cards, since endorphins are sizable molecules, which can’t easily pass through the blood and reach the brain. Their effect is only local, making muscles less tense and reducing discomfort.
Now it appears that in fact the euphoria experienced after physical exercise is actually due to endocannabinoids. These are chemicals released by the body, which are similar to the cannabinoids found in marijuana.
Their miniature size allows them to reach the brain and attach themselves to receptors. Their effect is to lighten the mood, bringing a sense of calm and happiness.
This was demonstrated through a lab experiment using healthy mice. Initially, experts determined the rodents’ anxiety levels, by placing them in cages with light and dark areas. It had been previously proven that anxious rats tend to stay in the shadows, so it was easy to assess the animals’ mood before the trial.
Afterwards, researchers had the rodents run on treadmills, to mimic the sensations experienced by human athletes.
Following the experiment, the animals had much higher blood levels of beta-endorphin and anandamide (an endocannabinoid). In addition, fewer mice spent time in the darkness of their cages, which suggested that exercise had made them more relaxed and calm.
In a subsequent trial, researchers blocked the animals’ brain receptors, which were supposed to receive endocannabinoids. This time, even after running, rats were just as anxious as before, and highly sensitive to physical pain.
The experiment was repeated by halting response to endorphins, while allowing endocannabinoids to stay active. On this occasion, the rodents did experience runner’s high, and appeared much calmer and tranquil.
Therefore, it appears that euphoria linked to strenuous exercise is actually due to these endocannabinoids. For too long, endorphins have been wrongly praised for providing us with euphoria and relaxation, when in fact their true function is limited to soothing pain.
Researchers point out however that in order to experience a real runner’s high a great distance should be covered: the mice included in the experiment had to run for 3 miles before effects on their mood became discernible.
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