Don’t like exercise? Your brain can change, study suggests

Exercise is a bit like cilantro: some people love it, others hate it. But what explains the gulf between those who dread going to the gym and those who fear missing even a single session there?

a new study of the brain’s signaling networks in the journal Medicine & Science in Sports & Exercise offers an optimistic outlook on the prospects of closing this gap. Stick with your exercise routine through those initially unpleasant weeks, the results suggest, and you, too, may learn to love the gym, thanks to long-term adaptations in the way your brain processes mood-altering chemicals. .

Previous studies have found that people who exercise regularly tend to have lower levels of anxiety and depression compared to less active people, and also get a greater boost in mood after a single workout. It’s a self-reinforcing cycle: You’re more likely to be motivated for your next workout if the last one made you feel good.

But it’s not clear how this cycle begins or what changes in brain chemistry make it possible. To find out, researchers at the University of Turku in Finland recruited 64 volunteers to complete a series of exercise tests and questionnaires. They used a medical imaging technique called positron emission tomography to measure the activity of mu-opioid receptors, or MORs, in the brain.

These MORs respond to the presence of endogenous opioids, the body’s own version of opioid drugs, and play a role in processing reward, pain, motivation, stress, and emotion.

“It is possible that some people are born with a more receptive REM system, and it helps them to tolerate and like exercise, and therefore it is easier for them to perform higher levels of exercise,” explains Tiina Saanijoki, lead author of the study. . “Or it could be the other way around, which is why a REM system has been developed that works best through regular exercise habits.”

Saanijoki put his volunteers through a test in which they cycled to exhaustion to assess their aerobic fitness. On another day, some of them did an hour of continuous moderate cycling and others a session of high-intensity interval training on the bike, to determine how different types of exercise affected opioid signaling.

Sure enough, the fittest subjects (as measured by both the cycling test and their self-reported levels of weekly exercise) saw the largest change in MOR activity after continuous moderate training. The same thing happened with heavier athletes after high-intensity interval training. It seems that the more exercise you do, the more satisfying it becomes neurochemically.

This still doesn’t prove that regular exercise leads to a more responsive opioid system, as opposed to the opposite. But the rat studies offer some suggestive evidence for the first explanation. For example, rats that exercise for five to eight weeks have higher levels of endogenous opioids, such as endorphins, circulating in their brains.

There is an important caveat here. The talk of opioids and endorphins may suggest that exercise triggers some kind of euphoric happiness in responders. That’s the impression that emerged from early research on what’s known as runner’s high in the 1970s, but subsequent studies have found such experiences to be extremely rare.

“Runner’s high is a pretty mythical thing, and maybe not worth focusing on too much,” says Saanijoki.

Instead, the sensations and emotions triggered by exercise tend to be subtle, sometimes operating below the level of consciousness, and likely mediated by several different sets of brain chemicals in addition to opioids, including endocannabinoids, the cannabis version of the brain.

Still, the findings suggest two key takeaways. The first is that if you don’t enjoy exercising, that doesn’t necessarily mean you’re doing something wrong. “I think we need to recognize that there is a huge variation between individuals in these responses, and not all people find exercise pleasurable or rewarding,” says Saanijoki.

The second is that this can change. Just as his body adjusts to a new exercise routine, so does his brain, and if Saanijoki’s hypothesis is correct, he’ll eventually wonder how he ever lived without it.

Alex Hutchinson is the author of Enduring: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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