Want to make sure your brain stays sharp and healthy as you age? Try doing some leg lifts. Why? Because people with fit legs tend to have fitter brains, at least according to a U.K. study that followed pairs of twins over a 10-year period.

The study, conducted by researchers at Kings College London, tracked 150 pairs of healthy twin sisters over the course of a decade. Researchers found that leg strength was a good way to measure a participant's overall health, and better overall fitness translated to a healthier mind as the participants aged.

The 300 women who participated in the study were between the ages of 43 and 73 when the study began. Researchers measured leg fitness at the beginning of the study using a piece of gym equipment that was modified to measure both speed and power during leg extensions. They also evaluated cognitive skills at the beginning and end of the study using computer tests that measured mental skills and the ability to process new information.

PHOTO BREAK: 15 houseplants for improving air quality

The end result was that the twins with fitter legs at the beginning of the study were more likely to maintain their mental health over the 10-year period. The fitter the legs, the better the cognitive skills and the fewer brain changes related to aging.

Lead researcher Dr. Claire Steves said: "When it came to cognitive aging, leg strength was the strongest factor that had an impact in our study." She added, "We think leg strength is a marker of the kind of physical activity that is good for your brain."

One reason leg muscles might be such good indicators of overall fitness is that they contain large muscle groups, the strength and power of which are generally maintained via exercises that are the result of good daily habits such as standing and walking.

This study adds more evidence to previous research on the link between exercise and mental health. And it offers up just one more good reason lace up those sneakers and get moving.