People who enjoy a good run every day may benefit from a condition known as "runner's high" in which an individual experiences a feeling of calm and exhilaration, according to a new study conducted by researchers in Germany.

Experts initially believed that runner's high is caused by a release of endorphins, considered to be the natural opiates produced by the human body. New research from the University of Heidelberg, however, suggests that chemicals called endocannabinoids and not endorphins are the ones responsible for this feel-good sensation.

In an experiment featuring laboratory mice, scientists from Heidelberg's Central Institute of Mental Health discovered the animals exhibited increased degrees of both endocannabinoids and endorphins after running.

The team also found that the mice showed less anxiety and less sensitivity to pain. The animals were calmer after their run, which was proven by their preference to spend more time in parts of their cage with more light instead of staying in dark areas.

When drugs were introduced to shut off the endocannabinoid receptors of the mice, the researchers observed that the mice no longer experienced a relaxing benefit from running and instead showed the same level of anxiety and sensitivity to pain as before the animals made their run.

Meanwhile, introducing opioid receptor blockers did not provide any effects on the tranquility the mice experience after running.

In a separate study conducted by University of Missouri (MU) researchers, internal opioid receptors were shown to have a significant impact in motivating individuals to run on pavements or on treadmills.

The MU paper suggests that mu-opioid receptors capable of releasing dopamine helped rats raised to enjoy running to become less motivated to carry out their exercise. This demonstrates that an individual's desire to run is directly influenced by these receptors. The scientists also discovered that blocking the mu-opioid receptors entirely lessened the amount of activity the rats made, albeit not to similar levels.

MU researcher Greg Ruegsegger said that the highly active rodents they observed in their study would constantly run on their wheels. He explained that when they activated the animals' mu-opioid receptors through chemicals, the rats showed a significant reduction in their amount of activity.

"Since exercise and addiction to substances follow this same chemical process in the brain, it stands to reason that activating these receptors in people with dangerous addictions could provide the same rewards they are craving without the use of dangerous drugs or alcohol," Ruegsegger said.

The recent Heidelberg paper, on the other hand, describes how far mice had to run to benefit from runner's high, showing that the animals needed to cover an average of more than three miles each day on their respective wheels.

Johannes Fuss, a researcher from the University of Heidelberg and lead author of the study, pointed out that humans could also benefit from the reduction of anxiety and pain sensitivity after running for long distances.

The findings of the University of Heidelberg study are featured in the journal Proceedings of the National Academy of Sciences.

Photo: Chris Hunkeler | Flickr 

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