Behav Neurosci. 2009 Aug;123(4):905-12. doi: 10.1037/a0015896.
Department of Psychology, Tufts University, 490 Boston Avenue, Medford, MA 02155, USA. [email protected]
Exercise improves cardiovascular health, strengthens muscles and bones, stimulates neuroplasticity, and promotes feelings of well-being. However, when taken to extremes, exercise can develop into an addictive-like behavior. To assess the addictive potential of exercise, withdrawal symptoms following injections of 1.0 mg/kg naloxone were compared in active and inactive male and female rats. Active and inactive rats were given food for 1 hr or 24 hr/day. Additionally, a group of inactive rats was pair-fed the amount of food consumed on the previous day by food-restricted active rats.
Rats fed for 1 hr/day decreased food intake and lost weight. Additionally, food-restricted active rats increased wheel running. There was a direct relationship between the intensity of running and the severity of withdrawal symptoms.
Active food-restricted rats displayed the most withdrawal symptoms, followed by active rats given 24-hr access to food. Only minimal withdrawal symptoms were observed in inactive rats. These findings support the hypothesis that exercise-induced increases in endogenous opioid peptides act in a manner similar to chronic administration of opiate drugs.