Physical activity and fitness in an international growth standard for preadolescent and adolescent children.

Concepts related to energy expenditure, physical activity and physical fitness, and methods of assessment are briefly considered. Variation in energy expenditure, physical activity, and physical fitness associated with age and sex during childhood and adolescence and relationships between physical activity and physical fitness in children and adolescents are reviewed. Implications of undernutrition and obesity for physical activity and physical fitness, and secular changes in physical activity and physical fitness, are briefly highlighted. The review concludes with specific recommendations for and limitations of inclusion of indicators of physical activity and fitness in the construction of an International Growth Standard for Preadolescent and Adolescent Children.