Abstract
Many children and adolescents in the United States do not meet the minimum recommendations for physical activity. In addition, both cross-sectional and longitudinal studies suggest that American youth become even more inactive as they mature. Girls are less active than boys at all ages, and minority youth demonstrate higher prevalences of physical inactivity. A large proportion of young people engage in sedentary behaviors such as watching television for prolonged periods of time. Data from the National Health and Nutrition Examination Survey and the Centers for Disease Control and Prevention show that at least 1 in 4 youth watch television and/or play computer games >4 hours per day. The prevalence of overweight and obesity in children and adolescents has increased dramatically in recent decades. Most studies have found a negative relationship between the amount of physical activity, especially of vigorous intensity, and the prevalence of overweight/obesity. Time spent watching television and playing on the computer was also predictive of overweight/obesity. Some studies have shown that sedentary behaviors such as prolonged television viewing may predict weight status in youth independent of physical activity level. Many studies using physical activity as an intervention to prevent weight gain or induce weight loss in youth suffer from methodological limitations that make it difficult to draw conclusions about the efficacy of these interventions or the volume and/or intensity of activity required. Limited evidence suggests that a greater volume of activity (>150 minutes per week) has the potential to achieve greater results. Better designed studies are needed to answer these important questions.