Physical fitness is the key to keeping your brain young. This is according to studies that looked at brain activity in people as they age.

We already know that exercise is good for our bodies. Daily exercise fights the loss of muscle tone and flexibility that tends to creep up with age. And it turns out, it has the same fountain-of-youth effects on our brains.

Studies show that over time our minds also become less flexible and nimble. We lose the ability to process new information or switch between mental tasks quickly — and now we know why.

A study published in the journal Neurology Clinical Practice examined nearly 100 individual studies on exercise and brain function and discovered exercising an average of 52 hours over six months are "associated with improved cognitive performance in older adults with and without cognitive impairment." The type of exercises that are beneficial include aerobic, strength-training and mind-body.

A study published in the journal Scientific Reports also looked at the link between fitness and cognitive performance, this time controlling for underlying causes that could distort results, such as body weight, education and age. The group of German scientists began by studying a large database of MRI brain scans, with an average age of 30 years old. A second round of testing had the volunteers walk as fast as they could for two minutes, followed by cognitive testing. Both tests revealed that a fitter body is associated with a fitter brain.

"It surprised us to see that even in a young population, cognitive performance decreases as fitness levels drops," said team leader Dr. Jonathan Repple. "We knew how this might be important in an elderly population which does not necessarily have good health, but to see this happening in 30 year olds is surprising. This leads us to believe that a basic level of fitness seems to be a preventable risk factor for brain health."

Young vs. old

In previous studies, neuroscientists have looked at the brain activity of young people and compared it with the brain activity of people over 40. While completing cognitive tasks, younger participants had brain activity that was highly localized. Depending upon what they were thinking about, the scans lit up exclusively in either the right or the left prefrontal cortex.

But the older participants used far more brain power to complete the same tasks. No matter the activity, the older volunteers tended to use both hemispheres of their brain.

In 2015, researchers from Japan's University of Tsukuba wanted to explore this idea by looking at the effect of exercise on this weakening of the brain. They tested the aerobic capacity of 60 Japanese men between the ages of 64 and 75 who did not show any signs of dementia or other mental issues. Next, they looked at the brain activity of each man as he completed a mental task. They found that the fitter a participant was, the less brain activity he used to complete the tasks when compared with his out-of-shape peers.

Of course, these studies alone can't draw a direct line between exercise and what's happening in the human brain. But it does build upon similar research, such as a study first mentioned by MNN's Lloyd Alter that looked at how exercise improved cognitive ability in older adults, and we covered another study that showed how daily exercise in your 40s can led to less brain shrinkage as you age.

Less brain shrinkage and more brain power? Sounds like some pretty good reasons to lace up.

Editor's note: This article has been updated since it was originally published in December 2015 and has been updated with new information.

Why exercise is good for your brain
The fitter you are, the stronger your brain will be as you age.