For years, scientists have wondered what causes that heavenly phenomenon known as the "runner's high." Initially, many speculated that endorphins were responsible for that feeling of euphoria that comes over me as I finish a long run.
New research points to a different factor: the "endocannabinoid system." I don't know exactly what they are, but I think I'm addicted, big-time.
Read on to learn more - and see you on the trail!
The New York Times: What Really Causes Runner's High?
Published: February 26, 2011
For decades, endorphins have hogged the credit for producing “runner’s high,” that fleeting sense of euphoria and calm that many people report experiencing after prolonged exercise. Who among us, after an especially satisfying workout, hasn’t thought, “ah, my endorphins are kicking in.” Endorphins are the world’s sole celebrity peptide.
Endorphins first gained notoriety in exercise back in the 1980s when researchers discovered increased blood levels of the substance after prolonged workouts. (Endorphins, for those who know the word but not the molecules’ actual function, are the body’s home-brewed opiates, with receptors and actions much like those of pain-relieving morphine.)
Endorphins, however, are composed of relatively large molecules, “which are unable to pass the blood-brain barrier,” said Matthew Hill, a postdoctoral fellow at Rockefeller University in New York. Finding endorphins in the bloodstream after exercise could not, in other words, constitute proof that the substance was having an effect on the mind. So researchers started to look for other candidates to help explain runner’s high.
Now an emerging field of neuroscience indicates that an altogether-different neurochemical system within the body and brain, the endocannabinoid system, may be more responsible for that feeling.
In a groundbreaking 2003 experiment, scientists at the Georgia Institute of Technology found that 50 minutes of hard running on a treadmill or riding a stationary bicycle significantly increased blood levels of endocannabinoid molecules in a group of college students. The endocannabinoid system was first mapped some years before that, when scientists set out to determine just how cannabis, a k a marijuana, acts upon the body. They found that a widespread group of receptors, clustered in the brain but also found elsewhere in the body, allow the active ingredient in marijuana to bind to the nervous system and set off reactions that reduce pain and anxiety and produce a floaty, free-form sense of well-being.
Even more intriguing, the researchers found that with the right stimuli, the body creates its own cannabinoids (the endocannabinoids). These cannabinoids are composed of molecules known as lipids, which are small enough to cross the blood-brain barrier, so cannabinoids found in the blood after exercise could be affecting the brain.
Whether this accumulating new science establishes, or ever can establish, definitively, that endocannabinoids are behind runner’s high, is uncertain. As Francis Chaouloff, a researcher at the University of Bordeaux in France pointed out in an e-mail, runners’ high is a subjective human experience. Still, endocannabinoids are a more persuasive candidate, especially given the overlap between the high associated with marijuana use and descriptions of the euphoria associated with strenuous exercise. One recent review article described them: “pure happiness, elation, a feeling of unity with one’s self and/or nature, endless peacefulness,” and “inner harmony.”