Background: Understanding the determinants of physical activity in children is critical for the treatment and prevention of childhood obesity. Social-cognitive theory has been used to understand behavioral patterns in children. Objectives: To explore the relationship between health beliefs, self-efficacy, social support, and sedentary activities and physical activity levels in children and to examine the relationship between physical activity and children's self-esteem. Methods: Ninety-two children aged 10 to 16 years completed the study. Physical activity was monitored for 1 week with a motion detector (Actitrac; IM. Systems, Baltimore, Md). Moderate-level activity and high-level activity were defined based on the results of treadmill testing. Health beliefs, self-efficacy, social influences, and time spent in sedentary behaviors were determined through questionnaires. Self-esteem was measured using the Piers-Harris Children's Self-Concept Scale. Chronic anxiety was measured with the Revised Children's Manifest Anxiety Scale. Results: There was a significant decline in physical activity levels between ages 10 and 16 years, particularly in girls. Preteen girls spent approximately 35% more time in low- and high-level activity than did teenage girls (P<.001). Overall, children spent 75.5% of the day inactive, with a mean+/-SD of 5.2+/-1.8 hours watching television, sitting at the computer, and doing homework. In contrast, only 1.4% of the day (12.6+/-12.2 minutes) was spent in vigorous activity. Time spent in sedentary behaviors was inversely correlated with the amount of moderate-level activity (P<.001) but not high-level activity. In contrast, time spent in high-level activity correlated with self-efficacy scores (P<.001) and social influences scores (P<.005). High-level physical activity was also associated with improved self-esteem (P<.05). Higher health beliefs scores were not correlated with physical activity levels. Conclusions: Children and adolescents are largely sedentary. Correlates of high- and low-level physical activity are different. Time spent on sedentary activities is inversely correlated with moderate-level activity, while self-efficacy and social influences are positively correlated with more intense physical activity. In addition, increased high-level physical activity is an important component in the development of self-esteem in children.
