To ward off age-related cognitive decline, you may be tempted to turn to brain training apps. Last year, consumers spent nearly $2 billion on them, some of which claim to improve cognitive skills.

Evidence suggests you’d be better off spending more time exercising and less time staring at your phone.

This year the World Health Organization released evidence-based guidelines on reducing risks of cognitive decline and dementia. Although it pointed to some systematic reviews that reported positive cognitive effects of brain training, the W.H.O. judged the studies to be of low quality. Among the studies’ limitations is that they measure only short-term effects and in areas targeted by the training.

There is no long-term evidence of general improvement in cognitive performance.

Instead of mind games, moving your body is among the most helpful things you can do. At least 150 minutes of moderate physical activity per week, including strength training, yields not just physical benefits but cognitive ones as well. But to be most effective, you need to do it before cognitive decline starts, according to the W.H.O.