In general, I tell my patients to exercise every day—or at least during weekdays, when they need to focus at school or work. Thirty minutes should do the trick, but more is better.
When it comes to exercise intensity, it differs for girls and boys. According to Rodney Dishman, Ph.D., of the University of Georgia, girls don’t need to exercise as vigorously as boys to derive the beneficial effects—30 minutes at 65 to 75 percent of maximum heart rate (about 220 minus your age). Boys and adults, on the other hand, should strive for 30 minutes at 75 percent of their maximum heart rate.