Many runners can attest to a feeling known as “runner’s high” after a long run. Runner’s high is hard to define, but it is a general feeling of calm and satisfaction after a run.
Runner’s high is commonly attributed to endorphins that are released during exercise. This conclusion makes sense, because endorphins help to relieve pain and discomfort. The blood levels that increase during exercise causes endorphin levels to rise. However, endorphins are large molecules that cannot pass the blood-brain barrier. So while they help the muscles in the body, they cannot actually affect the brain and contribute to a runner’s high.
A recent study with the Central Institute of Mental Health at the University of Heidelberg in Germany, and published in Proceedings of the National Academy of Sciences, reveals that runner’s high may actually be contributed to something called endocannabinoids. Endocannabinoids are chemicals in the body that lighten the mood.
The researchers studied healthy lab mice by placing them into cages and testing their anxiety levels. They then installed running wheels. Mice enjoy running even when they are not being pursued, leading to the belief that they do it because the find it to be enjoyable.
After running on the wheels, the mice experienced elevated levels of endorphins and endocannabinoids in their bloodstreams. They also appeared less anxious and were more tolerant to slight discomfort. These effects were not seen when the researchers used drugs to block the endocannabinoid system from working. In fact, the apparent runner’s high in the mice disappeared and they appeared to be more anxious. The researchers also tried blocking the mice’s responses to endorphins and leaving the endocannabinoid system alone, and found that the runner’s high remained.
Of course, mice and people are different. But cannabinoid muscles are small enough to pass the blood-brain barrier and attach to receptors in the brain, unlike endorphins.
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