You’ve probably heard it get chalked up to a rise in endorphins, the ‘happy’ chemicals that induce feelings of pain relief and pleasure. But it’s actually more complicated than that.
The ‘endorphins make you happy’ idea
The idea that increased levels of endorphins are responsible for that post-workout happy feeling came out of 1980s research that showed endorphin levels in the blood spiked after prolonged exercise.
Some researchers assumed these chemicals must also produce the sense of euphoria we feel after a workout.
But recent studies in mice suggest that endorphins actually might not have anything to do with the runner’s high.
The problem with the endorphin explanation is that they’re very large molecules – so large, in fact, that they can’t move from the blood into the brain.
The blood-brain barrier is key to keeping the brain safe, since it stops certain pathogens and molecules from passing from the blood into the brain.
Because endorphins can’t get through, it’s unlikely that they are the sole chemical responsible for the feelings associated with vigorous exercise.
Instead, scientists think the effect can be attributed to other chemicals in the body that produce similar pain-relieving and happy feelings.
Turning to endocannabinoids
Anandamide is a type of endocannabinoid, a chemical that’s part of the system that moderates the psychoactive, feel-good effects of marijuana. And unlike cumbersome endorphins, anandamide can smoothly make its way from the blood to the brain.