Some experts say 20 to 30 minutes per day of fast-paced activity is enough to get the brain going, while others recommend completing a complete 45 to 60 minute routine at least four times per week for optimal benefits. The amount of exercise you need will largely depend on your current fitness and endurance level and the type of exercises you are comfortable with. You can slowly raise your fitness level and build stamina by adding small increments of time to your workout so that your body can continue to release a healthy level of chemicals and hormones to keep your brain in good shape.