Fitness improves cognitive flexibility in older adults, according to a recent study.

Researchers at the University of Illinois at Urbana-Champaign found that older adults who are physically active have greater mental flexibility. One day soon, doctors may determine how physically active you are simply by imaging your brain.

"We want to know how the brain relates to the body, and how physical health influences mental and brain health in aging," Agnieszka Burzynska, who led the study, said in a statement. "Here, instead of a structural measure, we are taking a functional measure of brain health. And we are finding that tracking changes in blood-oxygenation levels over time is useful for predicting cognitive functioning and physical health in aging."

For the study, researchers looked at 100 adults between the ages of 60 and 80, and we used accelerometers to objectively measure their physical activity over a week. They found that spontaneous brain activity showed more moment-to-moment fluctuations in the more-active adults.

"In a previous study, we showed that in some of the same regions of the brain, those people who have higher brain variability also performed better on complex cognitive tasks, especially on intelligence tasks and memory,"

Burzynska said the new study highlights yet another way to assess brain health in aging.

"Our study, when viewed in the context of previous studies that have examined behavioral variability in cognitive tasks, suggests that more-fit older adults are more flexible, both cognitively and in terms of brain function, than their less-fit peers," researcher Art Kramer said in a statement.

The findings are detailed in the journal PLOS One.