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Background: Children tend to be sedentary during the after-school hours, and this has deleterious effects on their health. The objective of the present study was to determine the effects of a 3-year after-school physical activity (PA) program, without restriction of dietary energy intake, on percent body fat (%BF), cardiorespiratory fitness (CRF), and cardiometabolic markers in children.

Methods: A cluster randomization design was employed. A total of 574 3rd grade children from 18 elementary schools in the south-eastern United States participated. The intervention consisted of 80 minutes of age-appropriate moderate-to-vigorous PA each school day. The main outcomes of interest were %BF measured by dual-energy X-ray absorptiometry; CRF measured by heart rate in response to a submaximal step test; nonfasting total and high-density lipoprotein cholesterol (HDL-C); and resting blood pressure (BP).

Results: Intent-to-treat analyses showed significant treatment by time interactions for %BF (p=0.009) and CRF (p=0.0003). The change pattern of the means suggested that %BF and CRF in intervention children improved relative to control children during the school months, rebounding to the levels of control children over the summers following years 1 and 2. Year-by-year analyses of what occurred during the months when the program was offered revealed dose-response relations for %BF and CRF, such that the clearest beneficial effects were seen for those youth who attended at least 60% of the after-school sessions. No significant intervention effects were seen for cholesterol or BP.

Conclusions: An after-school PA program was effective in reducing adiposity and improving CRF, especially in the children who attended the sessions at least 3 days/week. However, the favorable effects on %BF and CRF were lost over the summer. Thus, it is critical to incorporate strategies that attract and retain the children to receive an adequate dose of PA year-round.


Yin, Z., Moore, J. B., Johnson, M. H., Vernon, M. M., & Gutin, B. (2012). The impact of a 3-year after-school obesity prevention program in elementary school children. Childhood Obesity, 8(1), 60-70.

DOI: 10.1089/chi.2011.0085

© Childhood Obesity, 2012, Mary Ann Liebert

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