Exercise Addicts Can Blame Their Brains

Aug. 28, 2009— -- Some people are so athletic -- running daily in rain, wind and heat in sickness and in health -- that most people wonder if they are masochists. But new research shows that they may just be addicted to exercise.

Stan Jensen, author of Run100s.com, has competed in 20 marathons and 125 ultramarathons in his lifetime. He said he considered each race "fun," but agrees there are sometimes other motivations at work among ultra runners.

"Take the Boston marathon: for a lot of runners that's their goal. They say 'wow that was hard, I'm glad I did it' and they go back to mowing the lawn," he said.

But Jensen wasn't satisfied. After many city marathons he moved to marathons on trails, and then he morphed to an ultra marathon, which is any race longer than the standard 26 miles in a marathon. Eventually, Jensen was doing 100-mile races.

Jensen's not alone in his enthusiasm. This week Robert Donahue of Minneapolis wanted to help recruit male mentors for his local Big Brothers Big Sisters. To do it, he decided he would run 100 miles in five days, which amounts to a little less than a marathon each day.

Other enthusiasts have set up races in horrible conditions such as the Badwater Ultramarathon in Death Valley (135 miles in temperatures up to 130 degrees), or the annual Antarctic Ice Marathon(82 miles in wind chills of -20).

Jensen insists that the soft trails and slower pace of an ultramarathon are easier on the body than the fast-paced pounding on pavement involved in most marathons. But ultramarathons lure runners who seek a challenge to keep up the "runner's high."

"There was a time at which I was definitely addicted to running. I enjoyed it, I enjoyed the way I felt when I ran and I enjoyed the feeling of accomplishment when I finished," said Jensen. "Running is also a form of escape. If you have chores, you have a choice: maybe I can just go run for a couple of hours and mow the lawn later."

But he will admit there's a bit of extreme thinking behind some among ultra marathoners.

"I also know people in my sport who are former alcoholics, or heroin addicts. They say 'you know, I have a problem with addiction, but this is the healthiest I addiction I can have'," said Jensen.

A new study in the August edition of the journal Behavioral Neuroscience showed running may indeed be addictive to the brain in the same way as heroin or morphine.

Runner's High Equivalent to Low Doses of Heroin?

Scientists have long known that exercising can release endorphins in the brain, and that some runners need to keep adding distances to feel that "high." However, it is not known if running forms a true addiction.

To test this, scientists turned to rats. It turns out rodents also keep increasing their amount of time on the running wheel like humans do.

Researchers at Tufts University let one group of rats become increasingly avid runners, and forced another group of rats to stay lazy in a cage with no hamster wheel.

When the researchers injected both groups of mice with a drug called Naloxone that is used for heroin withdrawal, the rats who had become exercise fanatics showed withdrawal symptoms similar to human heroin addicts on Naloxone -- their teeth shattered, and their bodies shook in tremors.

The unexercised mice, however, did not react to the Naloxone.

Could Running be Addictive for Everyone?

The rat study may provide only small amount of evidence that running is actually addictive in humans, but exercise experts didn't need much convincing anyway.

"It's not across the board that it's addictive, but it can be addictive," said Wayne Westcott, director of the exercise science program at Quincy College in Quincy, Mass. "Those are the people who over-train, they have bad feet, surgeries, or injuries and they can't stop."

Former professional runner Per Kristian Moerk agreed that brain chemistry could get people addicted to running. But that's only part of the picture, he said.

"I think the other part of why running is addictive is the feedback," said Moerk, manager for the sports medicine center at Wake Forest University Baptist Medical Center.

Moerk noticed runners also run to keep their bodies slim, have more energy during the day and for old-fashioned competition.

"You look better, your self-esteem improves. You get compliments," said Moerk.

But if running is so addictive, it begs the questions of what happened to all the rest of us who hate the tedium of the treadmill with a passion.

Why Aren't We All Addicted to Exercise

"In most things in life, and the things we research, there are responders to almost everything and there are non-responders," said Westcott. "Unfortunately, most people are not responsive to exercise and they don't seem addicted to exercise."

Indeed, 95 percent of us seem quite lazy. A 2003 study by the National Health and Nutrition Examination Survey (NHANES) outfitted 10,000 people across the United States with an accelerometer and tracked how long and how fast they moved during the day.

The results showed that less than 5 percent of adults older than 20 get at least 30 minutes of physical activity five days a week.

"That included activities of daily living, like working in the garden, and they could even do it in 10-minute segments," said Westcott.

According to Westcott, the physical activity standard in the NHANES trail amounted to walking 2.5 miles per hour, which is not even a brisk walking pace.

"Very few people are addicted, however the other 5 percent of us can get quite addicted to exercise," said Westcott. "I could cut off my leg and I'd still want to go exercise."

As for Jensen, he said his days of ultra marathons are dwindling.

"I lost motivation. I had accomplished what I dreamed of doing, and to me it was quite a feat. I didn't want to find something harder, I didn't want to beat myself," said Jensen. "Now I try to run one ultramarathon a year, just to be active."