Can running be addictive?

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© Peter Barrett/CORBIS

© Peter Barrett/CORBIS

As the saying goes, everything in moderation. While regular exercise is good for you for a host of reasons—reducing your risk for disease, helping to preserve cognitive abilities and protect mental health, and improving your overall heart health, to name some—according to a study of rats conducted by a team of psychologists at Tufts University, extreme and excessive exercise may be physically addicting, even triggering similar chemical responses in the brain as drug addiction.

The study, which tracked the behavior of both inactive rats and rats who ran for long periods of time on exercise wheels over the course of several weeks, found that, when given the drug naloxone—which is often administered to combat heroin overdose and triggers symptoms of withdrawal in heroin addicts—the rats who ran the hardest experienced strong symptoms of withdrawal, while those who had been sedentary had very little response to the drug.

Additionally, within the groups of active and inactive rats, the researchers distributed food differently—letting half of each group eat all day, while the rest were limited to just one hour of food intake. The intention was to mimic the psychological condition anorexia athletica, in which people become compulsive about overly frequent exercise to lose weight. Those rats who had run the most and consumed the least—mirroring the behavior of many humans with anorexia athletica—had the strongest symptoms of withdrawal, including trembling and drooping eyelids.

The study, published in the August issue of the journal Behavioral Neuroscience, may provide some insight into understanding how exercise—in moderation—could be used to help recovering drug addicts by creating similar reward sensations to those caused by their more dangerous habits. In conjunction with previous research on the subject, the psychologists write, these latest findings “suggest that it might be possible to substitute drug-taking behavior with naturally rewarding behavior”—possibly swapping a heroin haze for a runner’s high.