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runnerIt was long believed that the euphoria and general sense of wellbeing experienced after prolonged exercise was due to endorphins. However, German research now shows that the brain’s endocannabinoid system may be involved – the same receptors that are responsible for a marijuana buzz.

The researchers hit upon the endocannabinoid system as possibly being involved because they observed that endorphins can’t pass through the blood-brain barrier, team member Johannes Fuss told Scientific American. On the other hand, a lipid-soluble endocannabinoid called anandamide—also found at high levels in people’s blood after running—can travel from the blood into the brain, where it can trigger a high.

Anandamide was named after the sanskrit word ananda, which means bliss, because of the general feeling of wellbeing and pleasure it produces. It elevates mood, appetite, and lowers perception of pain.

In the study researchers taught mice to run on a wheel for an extended period of time. They then separated the mice into two groups – a running group and a sedentary group. The running group showed lower levels of stress and anxiety and less sensitivity to pain after their exercises than the sedentary group.

They then split the running group in parts and gave some mice endocannabinoid and endorphin antagonists – molecules that block the brain from receiving endocannabinoids or endorphins. Those mice that received endorphin antagonists showed the same results after their runs as the control group. However, those who received endocannabinoid antagonists showed the same level of stress and anxiety and sensitivity to pain as the sedentary group, even after extended periods of exercise.