Why does running make you feel happy?

 

Some people probably laugh when reading the title, because running can feel pretty awful. But apparently once you get past the initial sweat-hurricane/asthma attack/being dragged into the pits of hell part, running does start to feel good. And now, thanks to a study out of the University of Montreal, we know why.

As it turns out, running engages a system that is normally involved in making us feel full, which also activates the neurotransmitter involved in rewards and addiction.

“We discovered that the rewarding effects of endurance activity are modulated by leptin, a key hormone in metabolism. Leptin inhibits physical activity through dopamine neurons in the brain,” said Stephanie Fulton, a researcher at the University of Montreal Hospital Research Centre and lead author, in a press release.

Leptin is secreted by fat tissue; the amount in circulation on a given day reflects the amount of fat tissue you have. “The more fat there is, the more leptin there is and the less we feel like eating. Our findings now show that this hormone also plays a vital role in motivation to run, which may be related to searching for food,” explained Fulton.

Running to find food?

A common thought is that endurance running capacity in mammals—but especially humans—evolved in order to maximize the chances of finding food. The suggests that leptin plays a key role in this process by regulating energy balance and by encouraging behaviors that are rewarding in terms of metabolism, like running to find food.

The team studied two types of mice in cages equipped with running wheels: normal mice, and mice with the suppression of a molecule known as STAT3. STAT3 is found in the neurons that make dopamine in the midbrain, and without it, there was an enormous difference in the mice.

“Mice that do not have the STAT3 molecule in the dopaminergic neurons run substantially more. Conversely, normal mice are less active because leptin then activates STAT3 in the dopamine neurons, signalling that energy reserves in the body are sufficient and that there is no need to get active and go looking for food,” explained Maria Fernanda Fernandes, first author of the study.

In other words, leptin seems to discourage exercise in the other mice; blocking its action kept them highly active. This process probably happens normally in relation to body fat: If stores dip low, the brain gives encouragement to go get dinner. The same action seems to be happening in humans, too.

“Previous studies have clearly shown a correlation between leptin and marathon run times. The lower leptin levels are, the better the performance. Our study on mice suggests that this molecule is also involved in the rewarding effects experienced when we do physical exercise. We speculate that for humans, low leptin levels increase motivation to exercise and make it easier to get a runner’s high,” said Fulton.

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