It’s been known for some time that exercise can lift your mood, ward off depression, and help the brain age more gracefully — free of memory loss and dementia. But now researchers have found that even just one bout of exercise can — even better than a cup of coffee — improve your mental focus and cognitive performance for any challenging task you face that day. A new analysis of 19 studies involving 586 kids, teens, and young adults that was published Wednesday in the British Medical Journal found that short 10 to 40 minutes bursts of exercise led to an immediate boost in concentration and mental focus, likely by improving blood flow to the brain.