For many marathon runners, the reward for pushing themselves during the race extends beyond the finish line in the form of a hidden perk: runner's high.
But knowing what causes that euphoric feeling _ and how to achieve it _ has been a bit of a mystery.
First identified in the 1980s, runner's high has long been attributed to the body's release of endorphins, the feel-good hormones. But a flurry of research in recent years suggests that the source of that floaty sensation many runners experience might be more complex than previously believed.
Scientists from the University of Heidelberg led a groundbreaking study published last year that tested mice before and after spins on a running wheel. Not surprisingly, the mice were less anxious and less sensitive to pain after their runs.
But when the scientists suppressed the part of the brain that contains "endocannabinoids" _ chemicals that have the same relaxing effect on the brain as marijuana _ and tested the mice again before and after exercising, they found no change in the anxiety and pain levels. Thus, they concluded, the endocannabinoids were behind the runner's high.
But other research points to yet another source: a hormone called leptin that is linked to hunger feelings.
The theory involving leptin says that when we have lower levels of leptin, we are more likely to run farther like our ancestors had to in order to find food. On longer runs, some researchers believe, our bodies are more likely to achieve a runner's high.
