The data showed that, indeed, endorphins were produced during running and were attaching themselves to areas of the brain associated with emotions, in particular the limbic and prefrontal areas.
The limbic and prefrontal areas, Dr. Boecker said, are activated when people are involved in romantic love affairs or, he said, “when you hear music that gives you a chill of euphoria, like Rachmaninoff’s Piano Concerto No. 3.” The greater the euphoria the runners reported, the more endorphins in their brain.
“Some people have these really extreme experiences with very long or intensive training,” said Dr. Boecker, a casual runner and cyclist, who said he feels completely relaxed and his head is clearer after a run.
That was also what happened to the study subjects, he said: “You could really see the difference after two hours of running. You could see it in their faces.”