How much physical activity should teenagers do, and how can they get enough?

Many teenagers spend a lot of time being sedentary (sitting or lying down) at school or work, when travelling and during their free time. Modern conveniences such as smart phones, computers and food delivered to your front door encourage sedentary behaviour. But this lack of physical activity can have negative consequences for your physical and mental health.

We have all probably been told we have to exercise to stay healthy, but how much physical activity is the right amount for teenagers? And what are the benefits?