Life-long exercise habits are formed in adolescence, so it's important that parents encourage their teens to be active. That means some form of activity every day, with more vigorous activity (resulting in a sustained increased heart rate) at least 20 minutes a day three days per week. Whether it's on organized teams or through individual sports or exercise programs, the main message should be to get out and move. For instance, parents should encourage their daughters' interest in challenging activities, such as rock climbing, cycling, skiing or snowboarding. Try and make exercise a family affair. Go for a bike ride or hit the trails together. Give your teenager a pedometer and challenge her to collect at least 11,000 to 12,000 steps a day (the amount recommended for adolescents). Once she hits that figure, challenge her to more.