A brisk 20-minute walk every other day may be all it takes to stay sharp mentally as we age, according to a new study of exercise and cognition.

For the new study, published last month in the Public Library of Science journal PLOS ONE, scientists with the University of Kansas Alzheimer’s Disease Center tracked 101 sedentary older adults to see how much exercise could improve their brain function, The New York Times reports.

The seniors completed a series of tests, including measurements of their aerobic capacity and how well they could remember and think. The volunteers were then randomly assigned to one of four groups – one of which exercised for 75 minutes per week, which is half of the current federal recommendation, 150 minutes per week, 225 minutes per week, or not at all.

After 26 weeks, the results showed the more someone had exercised, the better their mental and physical fitness – including those who engaged in just 75 minutes per week.