ADVANCEMENT OF THE SCIENCE
cise was not good for their asthma (Mancuso et al., 2006). In another study that included 27 adults with mild to moderate asthma, exercise participation was rated only 1.6 on a 4-point physical activity scale (Garfinkel et al., 1992). Among children with asthma, the severity of the disease and parental beliefs about physical activity and asthma predicted the activity level, although this finding was based on self-reported data (Lang et al., 2004). Strengths and Limitations Measuring physical activity in children is dif- ficult. Compared with adults, children tend to have short bursts of activities that are more dif- ficult to measure (van Gent et al., 2007). The gold standard for assessing physical activity is the double-labeled water method (Westerterp, 2009). This method, however, does not provide data about activity patterns or intensity and is expensive and logistically challenging. Accel- erometers record the movement of the specific part of the body to which they are attached and thus dierences in types of physical activities are mostly accurate (van Gent et al., 2007) and correlate reasonably with the gold standard technique (Plasqui & Westerterp, 2007). The sample size was low due to the small number of students who have an asthma diag- nosis attending the school. A sizeable num- ber of repeated measurements, however, were obtained ( N = 102) during the 10 weeks of
the study. Additionally, GEE models allowed us to account for individual factors, which further validates the longitudinal associations with the mentioned trac-related air pollut- ants. Although this study was longitudinal, it was observational—as such, cause and eect cannot be inferred from the results. Further controlled studies are needed to understand the cause-and-eect relationship between air pollution and the physical activity of children with asthma. Conclusion To our knowledge, our study is the first to characterize the eects of trac-related ambi- ent air pollutants in elementary school chil- dren with asthma using objective measures of physical activity. Our findings suggest that school-based monitoring of air pollutants can oer insights into the health risk of children’s exposures and the impact on their physical activity. A higher concentration of trac- related pollutants over 72-hr and 96-hr expo- sures was strongly correlated with time spent in MVPA in children with asthma. During physical activity, an increased amount of air pollutant exposure could lead to increased asthma symptoms such as dif- ficulty breathing or bronchoconstriction, which might explain a decrease in time spent in MVPA with a subsequent increase in sed- entary behavior in an outdoor environment.
To ensure children obtain the benefits of exercise during the school day regardless of temporal fluctuations in air quality, school districts can site new schools away from high- trac roads, develop school zone transporta- tion policies that minimize idling of cars, and use barriers to mitigate air pollution exposure in outdoor areas of schools. Acknowledgements: This project was supported by a grant from the U.S. Department of Trans- portation (U.S. DOT) through the Center for Advancing Research in Transportation Emis- sions, Energy, and Health and funding from the Healthy Eating, Active Living Initiative of the Paso del Norte Health Foundation. The con- tents of this article are solely the responsibility of the authors and do not necessarily represent the ocial views of U.S. DOT. We thank David Perez, Adan Rangel, Ivan Ramirez, and Moi- ses Garcia for their help with field sampling. We are also grateful to the school principals, teachers, custodians, and personnel at El Paso Independent School District for the requisite permissions to conduct this research study. Corresponding Author: Leah D. Whigham, Center for Community Health Impact, Uni- versity of Texas Health Science Center School of Public Health, 5130 Gateway Boulevard East, El Paso, TX 79905. Email: leah.d.whigham@uth.tmc.edu.
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