Physical Activity and Public Health 12-1-2007 Objectively Assessed Associations between Physical Activity and Body Composition in Middle-School Girls : The Trial of Activity for Adolescent Girls June

Declining levels of physical activity probably contribute to the increasing prevalence of overweight in US youth. In this study, the authors examined cross-sectional and longitudinal associations between physical activity and body composition in sixthand eighth-grade girls. In 2003, girls were recruited from six US states as part of the Trial of Activity for Adolescent Girls. Physical activity was measured using 6 days of accelerometry, and percentage of body fat was calculated using an ageand ethnicity-specific prediction equation. Sixth-grade girls with an average of 12.8 minutes of moderate-to-vigorous physical activity (MVPA) per day (15th percentile) were 2.3 times (95% confidence interval: 1.52, 3.44) more likely to be overweight than girls with 34.7 minutes of MVPA per day (85th percentile), and their percent body fat was 2.64 percentage points greater (95% confidence interval: 1.79, 3.50). Longitudinal analyses showed that percent body fat increased 0.28 percentage points less in girls with a 6.2-minute increase in MVPA than in girls with a 4.5-minute decrease (85th and 15th percentiles of change). Associations between MVPA in sixth grade and incidence of overweight in eighth grade were not detected. More population-based research using Correspondence to Dr. June Stevens, CB 7400, Department of Nutrition, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 (e-mail: June_stevens@unc.edu).. NIH Public Access Author Manuscript Am J Epidemiol. Author manuscript; available in PMC 2008 June 1. Published in final edited form as: Am J Epidemiol. 2007 December 1; 166(11): 1298–1305. N IH PA Athor M anscript N IH PA Athor M anscript N IH PA Athor M anscript objective physical activity and body composition measurements is needed to make evidence-based physical activity recommendations for US youth.