Leg power may predict how well you think 10 years from now. In a study of 324 healthy identical twins, those with stronger legs did better than their siblings on cognitive tests a decade later. Their brains were bigger, too.

What’s so special about legs? They contain the largest muscles in the body, so strong legs are a good stand-in for overall fitness. (This study didn’t look at men, but others have found that fitness is good for the brains in both genders.)

So get those gams in shape with regular running, swimming, biking—or the most popular exercise, walking. Walk mindfully and you might get happier, too.

Just avoid these seven common walking mistakes.