For more than forty years, popular medicine and sports attributed the famous "runner's high"—that sudden sense of calm, analgesia, and quiet euphoria following sustained aerobic exercise—to the massive release of endorphins. However, an insurmountable physiological obstacle existed: endorphins are large peptides incapable of freely crossing the blood-brain barrier to modulate emotions in the central brain.
Contemporary research published by neuroscientists from institutions such as the University Medical Center Hamburg-Eppendorf revealed the true chemical architects: endocannabinoids, especially anandamide (whose name derives from the Sanskrit ananda, meaning "bliss" or "inner peace"). Unlike endorphins, anandamide is a small lipid molecule that the body synthesizes on demand during moderate, steady physical exertion, allowing it to flood brain tissue without any resistance.
Once in the central nervous system, anandamide binds to CB1 and CB2 receptors—the same ones targeted by the active compound of the cannabis plant. This interaction orchestrates three simultaneous therapeutic effects: it reduces amygdala reactivity (shutting down stress and fear signals), dampens the perception of peripheral pain, and increases dopamine release in reward circuits.
Evolutionarily, this biochemical cocktail did not emerge as a recreational reward, but as a vital survival tool: it allowed prehistoric hunters to sustain pursuit runs for hours despite physical exhaustion and minor muscle injuries.
Source: Proceedings of the National Academy of Sciences (PNAS)
