“Hot Bod” is a weekly exploration of fitness culture and its adjacent oddities.
There’s a beloved narrative about exercise — touted by doctors, by your marathoning college roommate, by scientists who study the brain and the body — that exercise might feel like challenging, tough, hard work while you’re doing it, but after? After, wow, you’re going to feel so, so good. And there’s well-supported evidence for this: After you exercise, endorphins explode! Your body floods with a natural high of feel-good chemicals. Endocannabinoids surge! But this result is far from a given, and not everyone feels this way. And as a new study shows, if you think working out will make you feel worse afterward, it will. Your expectations about exercise can dominate your entire experience of how exercise feels.
The study, titled “The Power of Words,” was published late last year in Medicine & Science in Sports & Exercise from researchers at the University of Southern Denmark. The study involved 83 volunteers, half men and women, who were divided into three groups that each received different messaging about exercise and pain. One group was told that exercise would increase pain tolerance afterward (true based on the body’s release of some pain-numbing hormones like endorphins); a control group was told nothing; and the final group was (erroneously) told that exercise would reduce pain tolerance afterward. For the study, each participant did a three-minute wall sit (wow, good job, long wall sit). When they finished, each had strong pressure applied to their muscles to test how much pain they could tolerate, compared to a baseline measured before the wall sit.
As shown on this chart, the neutral group (that wasn’t told anything) saw a significant increase in their pain tolerance. This was expected and in line with other studies about the body’s natural response to exercise. But interestingly, the group that was told they would have higher pain tolerance only had slightly more pain tolerance than the neutral group. And the group that was told exercise would make the pain worse not only had less pain tolerance when compared to the neutral group, but they experienced a complete decrease in pain threshold. In the words of the study’s author, Dr. Henrik Bjarke Vægter: “It wasn’t that it reduced the [analgesic effect of exercise], it completely blocked the effect that was in the two other groups. We were quite surprised that the negative information can have such a strong effect.”
Scientists have been studying the way exercise affects pain perception for a long time, and their theory goes something like this: After exercise, the body floods with chemical “anti-pain responses, [releasing] relaxing endorphins and endocannabinoids,” according to Dr. John Ratey, a Harvard professor and the author of Spark: The Revolutionary New Science of Exercise and the Brain. This has both a “local effect in the muscles and a more central effect in the brain where it’s all being processed,” says Dr. Ratey. So the active muscles will be more tolerant to pain and the brain in general will be more tolerant to pain. “After exercise, you are creating analgesia, you are creating the anti-pain environment in the body.” But, Dr. Ratey says, the two non-control groups’ responses were surprising.
“We expected that the group that got positive information would boost the effect even more,” says Dr. Vægter, the study’s lead author. “We actually didn’t see that. They had a larger increase in pain tolerance, but it was not very much more.” This leads to an interesting conclusion: “You don’t get more by believing very strongly,” says Dr. Vægter. “As a health-care practitioner, it doesn’t give you anything extra to boost expectation even further.”
The most fascinating result, to each doctor I spoke with, was the outsize power of negative expectation to completely offset the effect of the hormones released in the bloodstream. Here, we should highlight a central dynamic: the brain versus the body. New York University psychology professor Dr. Emily Balcetis, who studies conscious and non-conscious perception including in views toward exercise, puts it this way: “We have the power of the body versus the power of our mind. Which is going to win out! We would think it’s our body. Real physical, hormonal, chemical changes should be more powerful than temporary change in our thoughts, which is what this study is testing.” And yet they aren’t. During her years of study, Dr. Balcetis has seen something more complicated: “The mind can override the body.”
And not only can the mind be more powerful than the body, but bad thoughts can have more of an effect than good ones. Dr. Balcetis cites a standard truism of psychology: “negativity dominance,” which means that negative expectations and experiences are more powerful than positive ones. So, even though we’ve long known that exercise relieves pain, this study shows that if you don’t believe that, that won’t be your experience.
These insights are particularly meaningful for those with chronic pain, with whom the study was designed in mind (though the study explicitly recruited people without chronic pain to set a baseline). Many people who have chronic pain, Dr. Vægter notes, expect exercise to worsen their pain; and this experiment gives us much-needed insight into what effect this has. Dr. Vægter says it might be tempting to look at this study and think people just need to change their expectations; but the study actually shows that positive expectations aren’t that powerful. “Even though we tell patients that exercise is like a pain killer, that’s not what they experience and so that’s not a very useful way of trying to promote positive expectation,” says Dr. Vægter. “Once you have a belief this isn’t going to work for me, it’s really difficult to change that belief.” So rather than focusing on a positive outlook, Dr. Vægter thinks we should focus on recommending new exercise experiences that don’t come preloaded with negative associations.
Talking to doctors and researchers about the results of this study made me wonder about some of my painful experiences with exercise in the past. Did I experience all my stupid shin pain after running because of my expectations? Maybe, but I can’t just change that by knowing this fact; if the expectation of pain is there, it’s already pretty powerful. I could work carefully at removing my negative associations with running, but also, why? There are so, so many ways to move — and a million more that I don’t already hate, which will let me enjoy all of those bouncy chemicals after.