 How much exercise are you going to be doing during those minutes? So like hardcore heart rate at 250 sort of stuff? Navy SEAL nearing the point of brain explosion, yes. No, a new study involved scanning the brains of more than 10,000 healthy men and women age 18 to 97 found that those who walked, swam, cycled, or otherwise worked out moderately for 25 minutes a week even had bigger brains than those who didn't, whatever their ages, and healthier brains as well. Look at the big brain on Brad.