Not much beats the feeling you get after a long, hard run. It's the promise of that "runner's high," after all, that probably spurs you to get out the door and run in the first place. In fact, scientists say that exercise activates the reward centers in your brain similarly to drugs. (Yes, drugs — so "high" isn't hyperbole after all!)

But it turns out that it might be possible to activate those pleasure centers without exercise or drugs, according to new research from the University of Missouri.

In the study, just published in the journal Neuropharmacology, researchers bred two groups of rats. One group was bred to be extremely lazy, while the other group was bred to be extremely active. The scientists then messed with their mu-opioid receptors, which are basically the magnets for pleasure chemicals in rat (and human!) brains.

When researchers activated those receptors in the fit group of rats, the rodents actually didn't want to exercise as much. “These highly active rats would run on their wheels constantly,” lead study author Greg Ruegsegger said in a press release. “However, when we chemically activated their mu-opioid receptors, those rats drastically reduced their amounts 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.”

Another interesting finding was that, in rats at least, it appears fitter rats may be driven to be so fit because they have more of those pleausre receptors—400 percent more—than their lazy counterparts. Basically, when they exercise, they get more of a reward than the rats who, sadly, don't have as many receptors. Add that to your file on the role of genetics when it comes to whether you're inclined to exercise or have to use infinite willpower just to get to the gym.

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