Only runners know the high you can get from a good session pounding the pavement but scientists say that might not be from endorphins as once thought.
A new study, published this week in the Proceedings of the National Academy of Sciences, found that it might actually be endocannabinoids – essentially, internally produced marijuana – that is causing the sense of calm and euphoria at the end of a run.
According to the The New York Times endorphins first became a household word in the 1980s, when researchers found that blood levels increased after prolonged exercise. That made sense – exercise can cause a lot of discomfort or pain, and endorphins are the body opiates, with pain-relieving properties much like morphine.
So from that we took that it was also endorphins that produced the high after running.
But, it seems we were wrong.
In recent years, scientists have found that exercise raises endocannabinoids in the bloodstreams of people and animals.
For the new study researchers with the Central Institute of Mental Health at the University of Heidelberg medical school in Mannheim, Germany, rounded up healthy lab mice and tested their anxiety levels by putting them in cages with pockets of darkness and light (anxious animals stick to the shadows), and then gave them running wheels.
According to The New York Times mice generally like running, suggesting they get some sort of mental satisfaction from it.
The scientists noted elevated levels of both endorphins and endocannabinoids in the animals’ bloodstreams after running. They also found the animals were more tranquil after running. When the scientists used drugs to block the endocannabinoids the mice had no post run high suggesting it is these that provide all the pleasure.
Whether it translates to humans is yet to be tested.