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People who like to use their brains are a lot less physically active than people who don't, according to research published this month in the Journal of Health Psychology.

Now, you may think this isn't terribly surprising. Smarter people are probably more likely to go to college and take jobs that require more brainpower - engineers, lawyers, (ahem) reporters - than strength and physical skill - construction workers, carpenters, pipe fitters. People in brainier jobs are more likely to sit at a desk all day than people who build houses or fix things for a living, so of course smarter people will be less physically active. Right?

But that's not quite what this study says. Rather, it finds that people who like to use their brains aren't necessarily smarter than those who don't. But they are a lot more comfortable being still with their thoughts.

To arrive at their finding, researchers screened a bunch of undergraduate students and recruited two groups to participate in the study: students who had a high "need for cognition" (NFC), and students with a low need for cognition.

NFC is a long-standing metric in psychological research. The paper's authors describe it as "a tendency to engage in and enjoy effortful cognitive endeavors." It's measured via an 18-question survey that asks people things like whether they "like to have the responsibility of handling a situation that requires a lot of thinking" or whether they "like tasks that require little thought once I've learned them" or if thinking is "their idea of fun."

In this study, the researchers took 30 students whose responses indicated they had a high need for thinking in their daily lives, as well as 30 who had a low NFC. For a week, they had each student wear an actigraphy device - kind of like a precursor to the Fitbit for measuring daily physical activity. The devices recorded activity levels every 30 seconds. The researchers excluded periods when the students were sleeping, or when they removed the devices, which was rare.

They then looked at the daily differences in physical activity between the high-NFC and low-NFC groups, measured in terms of instances of gross motor activity - activity that involves moving arms and legs, like walking, dancing, exercising, etc.

Students with a lower need for cognition showed a higher frequency of physical activity on every day of the week during the study period. According to the researchers' statistical analysis, this difference in activity was highly significant during the weekdays, but the differences in the weekend readings weren't as meaningful (despite the seemingly big difference on Saturday, the authors indicated that that was likely due to statistical noise).

The first thing to note here is that this isn't simply a function of smarter people self-sorting into more sedentary jobs. All of the subjects were undergraduate university students who had not yet started their careers. It's possible that there's an even greater difference in physical activity between undergrad high-NFC individuals, and low-NFC individuals of the same age who aren't enrolled in college.

The second key point is that a need for cognition is a different metric than simple intelligence. People with lower IQs can enjoy a contemplative life and a good cognitive challenge, for instance. Similarly, plenty of people with high IQs dislike using their brain in challenging ways.

The study's findings suggest that the relationship between brainpower and physical activity works in more subtle ways than most of us might have expected. For instance, think of two engineers working the same job in the same company. You might expect them to show the same amount of physical activity over the course of a day.

But the high-NFC engineer enjoys the mental challenges of her job and spends most of her day at her desk, grappling with the intricacies of complex problems. The low-NFC engineer, by contrast, dislikes being challenged mentally by his work. He fidgets, paces, takes multiple bathroom breaks, maybe goes for a jog at lunch.

"High-NFC individuals seem more content to 'entertain themselves' mentally," the study's authors write, "whereas low-NFC individuals quickly experience boredom and experience it more negatively."

On balance, the high-NFC engineer above is probably more satisfied with her job. But given everything we know about the health benefits of physical activity, her tendency toward being more sedentary than her fidgety co-worker may be a harbinger of health problems down the road.

Beyond that, the study suggests that we should also give a little more benefit of doubt to the slackers in our lives. They may not be truly lazy, they may simply be living the life on the mind.