Many people appear to be addicted to exercise. They work out with a religious fervor, and when they miss a session, they feel ill, severely anxious or depressed, much in the manner of drug addicts who experience withdrawal symptoms.
The first theory about the cause of exerciser’s high ascribed it to an increase in the level of catecholamines in the body, such as norepinephrine, epinephrine and dopamine. All of them have potent stimulant effects, and all are increased by exercise. The theory made sense initially.
Continued research, however, revealed the existence of the brain’s natural opiate system. Among the natural painkillers, or brain analgesics, are enkephalins and endorphins, which are structurally similar to morphine but thousands of times more potent in pain reduction. Scientists investigating the relationship between endorphins and exercise noted that since the chemicals were stimulated by pain, it would likely take either a high level of exercise intensity or extended exercise, such as a long-distance run, to activate endorphin release.
Further study revealed several flaws in the opiate/exercise theory as well. The first was that the natural opiates could be measured accurately only in the blood, but the sensations linked to the flow of opiates occurred in the brain. Second, stimulating the opiate system led to certain effects not seen with exercise, such as severe respiratory depression, which is a primary cause of death from opiate overdose; pinpoint pupils; and inhibition of gastrointestinal motility, resulting in the mother of all constipation cases. In addition, endorphins that appear in the blood are too large in structure to pass through the protective blood-brain barrier, and thus cannot enter the brain, where the action is.
The latest explanation for exerciser’s high follows the discovery of receptors in the brain for THC, the active ingredient in marijuana. Scientists now know that the body produces its own version of marijuana. In fact, a new type of diet drug is based on blocking that system. Those who smoke pot, even those who might not have inhaled, know that using weed promotes a voracious appetite. Blocking the brain’s endocannabinoid receptors, as the THC receptors are called, leads to a dramatic loss of appetite for sweets. Conversely, stimulating those receptors increases appetite.
Two types of endocannabinoid receptors have been identified, as well as two substances that interact with the receptors, or ligands.1 One is called anandamide, and the other 2-AG. (Chocolate may contain some naturally occurring anandamide, which may partially explain why some people crave chocolate.)
Activation of the endocannabinoid system leads to pain reduction and alters emotions and thinking processes. Receptors for the body’s natural cannabinoids exist in muscle, skin, endothelial cells and lungs. Many scientists now believe that exerciser’s high may result from activation of cannabinoid receptors.
On the other hand, scientists also say that exerciser’s high happens only during endurance events, and that brief, intense activity, which would include bodybuilding workouts, isn’t long enough to activate it. Painful stimulation of skin, however, activates the endocannabinoid system. In running, the activation may be brought on by the constant foot pounding, causing painful foot stimulation. It’s also reasonable to assume that an intense weight-training session, which includes an abundance of pain, would activate the endocannabinoid system. Many of the same feelings long-distance running brings on also appear after a hard weight workout.
The good thing about activating the endocannabinoid system is that the serious side effects of using drugs, such as respiratory depression and constipation, don’t occur. That’s because there are few receptors for the cannabinoids in the brain stem, where breathing is controlled, or the large intestine, the site of constipation.
Anandamide is known to reduce edema and inflammation, while blocking the pain associated with the release of lactic acid. Since lactic acid release leads to a burning sensation in muscles and signals the end of any particular set, activating the endocannabinoid system should theoretically enable you to train harder. Attempting to cut to the chase by smoking pot before training won’t have similar effects because of the intense relaxation produced by pot, which makes you want to do anything but train. Natural cannabinoids have a reverse effect: They reduce sedation while also reducing feelings of anxiety. That could explain the finding that exercise relieves the anxiety-producing effects of caffeine.
Activating the endocannabinoid system may also explain exercise addiction. The feel-good effect produced during exercise can result in a craving for such feelings. When they aren’t assuaged by a workout, a type of mental withdrawal can occur, such as depression or anxiety.
Anandamide acts as a vasodilator, meaning that it dilates blood vessels. That would result in a greater degree of muscular pump during training and greater delivery of oxygen and nutrients to working muscles. Since endocannabinoids act as bronchodilators, they also promote better breathing during exercise and may even help those afflicted with diseases characterized by difficulty in breathing, such as asthma.
The work relating endocannabinoids to exercise is still preliminary, but so far the results make sense. The substances may explain why so many are motivated to exercise and why exercise makes us feel so good.
1 Dietrich, A., et al. (2004). Endocannabinoids and exercise. Br J Sports Med. 38:536-41.
©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
