Exercise is a powerful drug. It seduces many with its zen-like state a feeling that was coined the "runner's high" in the 1970s. The lure of exercise can even turn enthusiasts into addicts.

"I'm addicted to the high of exercising," says 22-year-old Vanessa. "I can't wait to ride the bike so I can start feeling good. I'm not sure why it happens, but it's like a feeling of relief."

It is common knowledge that exercise produces many mental benefits in addition to all the physical benefits. There is something about exercise that makes us feel better. But what causes that feeling? Can we really become addicted to it?

The Mythical Endorphin Rush

For years the rush has been thought to be caused by endorphins (endogenous hormone-like substances produced in response to stress or pain). Because exercise is a form of stress, our bodies release endorphins when we exercise. Proponents of the endorphin rush believe that these molecules change the way we feel, thus giving us that high after working out.

Jack Raglin, PhD, associate professor in the department of kinesiology at Indiana University in Bloomington, Indiana, contends that the endorphin rush is more hype than fact. "Your body does release endorphins when you exercise," he says, adding that endorphins are usually released when exercise levels are moderate or when exercise sessions are lengthened. "But there's no strong evidence that endorphins change the way you feel."

Is It All in Your Head?

Research indicates that psychological factors may be a cause of the exercise high. In a study published in the journal Health Psychology, researchers at the University of Illinois Urbana-Champaign recruited 46 undergraduate women and divided them into two groups. None of these women exercised more than once a week.

All 46 women underwent fitness tests on a stationary bike. No matter how they had performed, women in one group were told they had excellent test results. Women in the other group were told they had below average results.

Several days later, researchers asked the women to exercise again. Each woman was reminded of her previous performance. Then, every 20 minutes during a workout on the Stairmaster, researchers asked the women how they felt. Women who had been told they had done well on their first test responded more positively than women who had been told they had done poorly. That confidence, researchers concluded, may contribute to the high people feel after exercising.

"These findings suggest that increases in perceived efficacy (like mastery, competence, and control) are at least one source of the positive psychological response experienced post-exercise," says Edward McAuley, PhD, professor in the department of kinesiology at the University of Illinois and lead author of the study.

Addicted to the High

Can those positive experiences, or that high, become addictive? Yes, says Raglin. However, issues other than the feel-good experience can cause people to abuse exercise.

So if endorphins are not to blame, what is? Raglin says psychology plays a larger role than physiology in causing people to abuse exercise. Certain personalities may predispose people to developing an addiction to exercise. People with obsessive-compulsive disorder, for example, may be more prone to developing a heavy reliance on exercise. For others, exercise becomes a coping mechanism. "They deal with their stresses through exercise," Raglin says.

When Exercise Becomes Unhealthy

Exercise addiction or abuse was first analyzed by Dr. William P. Morgan in 1979. Morgan studied runners and discovered that excessive exercise can cause physical and mental harm. Since then, researchers have learned that recreational and serious athletes in any sport can abuse exercise.

According to Raglin, people who abuse exercise exhibit three common characteristics:

  • Excessive reliance on exercise
  • Continuation of exercise when injured or sick
  • Withdrawal symptoms when exercise levels are decreased or temporarily halted

Essentially, exercise becomes the number one priority in life for exercise addicts, and all activities are scheduled around working out. They often ignore careers, friends, spouses, and children. In fact, exercise abusers may even lie about their workout patterns.

The more involved they get with exercise, the deeper their addiction grows. Because they are never satisfied with the amount of exercise they get, they continue to increase the dose. They often feel a loss of control, and they become so dependent on their workouts that they cannot and will not stop, no matter what the cost. In many cases, their dependency on exercise is not evident until something like a job, family or injury interferes with their daily routine.

They also disregard warning signs of physical ailment. Even when they are sick or injured, they continue to push themselves. Sometimes the consequences of exercising while injured can lead to permanent physical disability that prohibits future exercise.

A Healthy Habit Overall

Unfortunately, there are no estimates about how many people abuse exercise. There is also little recognition of the problem, largely because exercise is a healthy habit.

Fortunately, though, the majority who work out will not abuse exercise. Everyone who exercises, no matter what their level of fitness, can experience that rush from being active and living life to its fullest.