Gym junkies, workout warriors, endurance enthusiasts of all shapes and sizes: Slow down a minute. This could be a bit confusing.
That endorphin-fueled rush, that rare wave of euphoria you chase like a pot of gold at the end of your sweat-soaked rainbow? No one is sure whether it really exists. Or precisely what causes it.
When researchers set out to determine whether killer workouts can produce enough of the opiate-like hormone to bring on that buzz, the notion turned out to be another fitness Sasquatch. Maybe it's there. But different people describe widely different things.
"The hypothesis that endorphins are responsible for changes in euphoria and other moods during or after acute exercise remains plausible, but it has been perpetuated with little evidence," University of Georgia researchers Rod Dishman and Patrick O'Connor wrote in 2009.
As far back as 1999, John Raglin, a sports psychology researcher at Indiana University, wrote in an article for physical trainers: "Endorphin has also been identified as the reason people sometimes appear to get a 'high' from exercise or even become addicted to it. Yet, no compelling scientific evidence backs any of these claims."
But then German researchers used new brain imaging technology in 2008 to examine the production of endorphins in the brains of 10 experienced athletes after a two-hour run. Their research showed the level of endorphins in the brain correlated with the runners' descriptions of their mood
change during the workout. But other research identifies substances in the body that are more like the active ingredient in cannibis as the possible cause of the euphoria.
So are we all exercising in the grip of an unproven legend? Or is there something to this?
The idea that endorphins flood our brains in sufficient quantities to create a druglike buzz is virtually an article of faith in gym conversations and fitness publications.
Research also has clearly established the benefits of exercise on anxiety, depression and mood in general.
"It's the sexiest explanation," Raglin said in an interview.
Thirty years ago, researchers embraced endorphins as the logical explanation for both runner's high and exercise addiction because of their similarity to opiates, such as heroin and morphine; their proven painkilling properties; and their role in regulating the central nervous system, according to Dishman and O'Connor's research.
Researchers then blocked endorphin receptors in some subjects but found no difference in the effects of exercise on mood changes. Others tested the blood of subjects after strenuous exercise and discovered lots of endorphins, which are also produced by the adrenal glands, Raglin said.
The problem is these hormones don't effectively cross the barrier that keeps most of the blood supply out of the brain. And there are other hormones, as well as temperature and blood pressure changes, that may be part of unusual feelings after a hard workout.
Then, there are common-sense tests. If endorphins are produced by vigorous exercise, and "runner's high" is caused by endorphins, why are such episodes uncommon enough that they are prized by people who work out? Why do people describe the feelings so differently? And if endorphins lead to exercise addiction, why aren't more people afflicted with that problem?
"Not many people become addicted," Raglin said. "And people who become addicted look terrible," he said, unlike those who describe episodes of runner's high as an extremely pleasant experience.
Feeling somewhat cheated? Join the crowd.