Assessment of Physical Education Time and After-School Outdoor Time in Elementary and Middle School Students in South Mexico City: The Dilemma between Physical Fitness and the Adverse Health Effects of Outdoor Pollutant Exposure. - Villarreal-Calderón, Anna; Acuña, Hilda; Villarreal-Calderón, Jessica; Garduño, Mónica; Henríquez-Roldán, Carlos F.; Calderón-Garcidueñas, Lilian; Valencia-Salazar, Gildardo (Archives of Environmental Health, 2002)