Thank you for your article. It’s well written. Maybe you find this interesting. You say: “ When you reach a certain level of intensity in cardio (the level differs person to person), the brain releases endorphins, its natural painkillers, and that’s when you experience the fabled ‘runners high’.”

Research from 2015 showed that:
“Endorphins are the body’s natural painkillers. Back in the 1980s, scientists found that endorphin levels in the blood spiked after prolonged exercise. From there, people made the logical leap to assume that these chemicals also produced the sense of euphoria in the brain. But there’s a problem with this theory. Endorphins are big molecules, and are too large to fit through the brain’s gatekeeper — the blood-brain barrier. So there’s no way they could be responsible for the post-run high.

Researchers have spent the last decade looking for other explanations, which led them to cannabinoids. Found in marijuana, these chemicals compounds are small enough to cross the blood-brain barrier and bind to receptors in the brain. And recent research has found higher levels of endocannabinoids (the ones the body produces naturally) in the blood of people and animals after exercise.”

In practice it doesn’t really matter what causes the high. But you seem to be also interested in the underlying working of things. Thanks again for your article.