If the benefits of physical activity were made into a pill, everyone would be on it. Studies show that moving improves nearly every aspect of health: boosting sleep, strength, and mental well-being. Still, most people don't exercise nearly enough. According to data published in 2023, less than a third of U.S. adults get the government-recommended amount of physical activity in their free time: at least 20 minutes of moderate-intensity aerobic exercise per day, plus a couple of muscle-strengthening sessions each week.
Why is it so tough to get people to do something so good for them? Physical limitations, health problems and modern life are certainly factors for many people. But research suggests there's another factor: our brains don't want us to exercise. For most of human existence, people had to be physically active to carry out the basic functions of life, such as finding food. Humans evolved (进化) to tolerate a high level of activity — but also to conserve energy for when movement was unnecessary, explains Daniel Lieberman, a human evolutionary biologist. As a society, we no longer move much in daily life, but the evolutionary instinct (本能) to conserve energy remains, Lieberman says. "That voice 'I don't want to exercise,' is completely normal and natural," he says.
Physical-activity researcher Matthieu Boisgontier demonstrated that phenomenon in a 2018 study. He gave people control of a digital avatar (化身) while they were connected to brain-activity monitors. They were instructed to move the avatar away from images of sedentary (久坐的) behavior that appeared on screen and toward images of physical activity. The study found that avoiding sedentary behavior took more brain power, suggesting that we have an "automatic tendency" to pick relaxing over moving.
That conclusion shows up repeatedly in research. Studies show, for example, that people consistently choose to take a lift instead of the stairs. "That natural instinct isn't bad — it's just that modern life gives us so many chances to give in to our preference for rest that we have reached an extreme that is no longer beneficial to our health," Boisgontier says.