Picture a dedicated distance runner. You probably wouldn't imagine him or her going behind the garage to get high. Runners, though, get high more than almost anyone else. They are like junkies, jonesing for a chemical rush. However, their fix is delivered not by huffing some illegal chemical, but by the body itself through exercise.
He might not have inhaled, but President Clinton certainly got high (AP)
The key is opioids
. These chemicals take their name from the opium poppy, where they were first discovered. While this name conjures images of illegal narcotics, the body naturally produces these substances, which include such innocuous neurotransmitters as endorphins. The body also contains many receptors that mediate the effects of opioids. When an opioid receptor captures one of these chemicals, it can trigger reactions that include pain relief, sedation and even euphoria.
In this 2008 study, several runners were PET scanned before an endurance run (roughly 10 miles at a moderate pace). After the run, they were scanned again, and this time, opioid receptors in their brains were significantly less likely to be open for picking up an opioid chemical. This means that the receptor has already captured an opioid.
In the second part of the experiment, greater uptake at these receptors was correlated with reported feelings of "euphoria". Putting the pieces together: sustained running causes release of opioids in the brain, which, when captured by receptors, cause an increase in reported feelings of euphoria.
Next time you are feeling down, try going for a run. It has long been common sense that this will make you feel better. Now it is "scientific sense" too.