Physical activity and BMI in a nationally representative sample of children and adolescents

To examine objectively measured physical activity levels by age, sex, and BMI for children and adolescents in a nationally representative sample.

Data were from the 2003-2004 and 2005-2006 National Health and Nutrition Examination Surveys, which included physical activity assessment by accelerometer and measured height and weight. The authors calculated minutes of moderate and vigorous activity.

Boys were more active than girls, and activity levels were lower at older ages. Younger children met daily recommendations for physical activity, whereas older children, especially girls, did not. Typically, weight status was inversely related to activity, though differences were less apparent among boys. Underweight children were not always more active than heavier peers.