But now medical technology has caught up with exercise lore. Researchers in Germany, using advances in neuroscience, report in the current issue of the journal Cerebral Cortex that the folk belief is true: Running does elicit a flood of endorphins in the brain. The endorphins are associated with mood changes, and the more endorphins a runner’s body pumps out, the greater the effect.

Leading endorphin researchers not associated with the study said they accepted its findings.

“Impressive,” said Dr. Solomon Snyder, a neuroscience professor at Johns Hopkins and a discoverer of endorphins in the 1970’s.

“I like it,” said Huda Akil, a professor of neurosciences at the University of Michigan. “This is the first time someone took this head on. It wasn’t that the idea was not the right idea. It was that the evidence was not there.”

For athletes, the study offers a sort of vindication that runner’s high is not just a New Agey excuse for their claims of feeling good after a hard workout.

For athletes and nonathletes alike, the results are opening a new chapter in exercise science. They show that it is possible to define and measure the runner’s high and that it should be possible to figure out what brings it on. They even offer hope for those who do not enjoy exercise but do it anyway. These exercisers might learn techniques to elicit a feeling that makes working out positively addictive.

The lead researcher for the new study, Dr. Henning Boecker of the University of Bonn, said he got the idea of testing the endorphin hypothesis when he realized that methods he and others were using to study pain were directly applicable.

The idea was to use PET scans combined with recently available chemicals that reveal endorphins in the brain, to compare runners’ brains before and after a long run. If the scans showed that endorphins were being produced and were attaching themselves to areas of the brain involved with mood, that would be direct evidence for the endorphin hypothesis. And if the runners, who were not told what the study was looking for, also reported mood changes whose intensity correlated with the amount of endorphins produced, that would be another clincher for the argument.