Children and teens require more than twice the amount of moderate-to-vigorous physical activity that adults need — 60 minutes a day. But research shows that just about 42% children ages 12 and under meet the guidelines of 60 minutes of moderate-to-vigorous physical activity every day. Among teens, fewer than 9% do. Moderate-to-vigorous activity is crucial for bone growth and muscular development. Vigorous exercise, like running and playing energetically, so that the heart beats faster and breathing is more rapid, may determine whether the calories children consume are used to multiply lean muscle cells and build strong bones. Sedentary behaviour, in contrast, will convert excess energy into fat cells.