This study gives the term “gym rat” a whole new meaning:
“Excessive running shares similarities with drug-taking behavior,” write researchers in the August issue of Behavioral Neuroscience, published by the American Psychological Association.
Basically, rats who were given a drug that produces withdrawal in heroin addicts went into withdrawal after running excessively in exercise wheels (not unlike treadmills). The rats that ran the hardest had the most severe withdrawal symptoms; the inactive rats barely suffered withdrawal.
If you work out regularly, you know how good a strong Runner’s High can feel (and you need not be a runner to attain it.) You soar, you glow, you feel on top of the world. It’s not hard to see how that kind of elation could be addicting. (Unfortunately, for some people, it does become an addiction – there’s a potentially fatal eating disorder called anorexia athletica in which working out becomes as compulsive as taking drugs, resulting in significant, unhealthy weight loss.)
The good news from this study: The authors think that if excessive exercise is addicting, then perhaps drug addicts could use moderate exercise instead of drugs when quitting.
For your science buffs, here’s how the study worked: For several weeks, 44 male and 40 female rats were allowed to either run in exercise wheels or remain inactive. To simulate anorexia athletica, the researchers divided the active and inactive rats into groups whose members were either given food for one hour a day or around the clock. Rats in all four groups were then given naloxone, a medicine for heroin overdose that produces immediate withdrawal symptoms.
Active and inactive rats responded very differently to naloxone, which was given in proportion to their weight. The active rats showed withdrawal symptoms like those seen in narcotics addicts: trembling, writhing, teeth chattering, and drooping eyelids.
The active rats who had access to food for only one hour a day both ran the most and displayed the most severe withdrawal symptoms. Like people with anorexia athletica, they ran so much that they lost significant amounts of weight. Additionally, the more a given rat had run, the worse its withdrawal symptoms after naloxone. In contrast, regardless of how much they ate, inactive rats responded very little to the drug.
Because of the way the active rats responded to naloxone, they seemed to have undergone the same changes in the brain’s reward system as rats addicted to drugs. “Exercise, like drugs of abuse, leads to the release of neurotransmitters such as endorphins and dopamine, which are involved with a sense of reward,” notes lead author Robin Kanarek, PhD, of Tufts University.