Am J Health Behav.™ 2014;38(3):379-391 379 T he Physical Activity Guidelines for Americans recommends that children and adolescents participate in at least 60 minutes of moder- ate-to-vigorous physical activity (MVPA) each day. 1 However, a national study 2 indicated that only 15.3% of high school students met the national recommendations for aerobic physical activity. This igure is well below the Healthy People 2020 national objective of 20.2% (physical activity – 3. 1). When further examining the high school students subgroups, only 8.4% of the girls (as opposed to 21.9% of the boys), and 15% of the non-Hispanic African Americans 2 met the aerobic physical activ- ity objective, indicating major differences within these subpopulations. Racial/ethnic disparities in overweight grow as the rates accelerate among Afri- can Americans. 3 Indeed, 27% of African-American girls ages12 to 19 are overweight compared to the 15.5% national statistic of the same age group. 4 Research indicates that inadequate physical ac- tivity is one of the major contributors of obesity among African Americans. In particular, problems of low accessibility to physical activity facilities and safety are more pronounced in urban, low-income neighborhoods. African-American adolescents, who are more likely to live in these locales, are less likely to have available facilities/locations that facilitate physical activity such as parks, school yards or community centers. 5 Assessing physical activity in this subpopulation can provide policy- makers, healthcare providers, health educators, and public health oficials with important informa- tion to guide the distribution of initiatives and re- sources to reduce or eliminate health disparities. A common framework for examining physical activity is the social ecological model. 6-9 Ecological models 9 depict reciprocal interactions in multiple levels, including intrapersonal, interpersonal, or- ganizational, community, and public policy. This model is well suited for studying physical activ- ity patterns, because physical activity is often conducted in speciic physical environments (eg, locations) under certain social environments at a given time. 6 The physical environment or loca- tion of physical activity indicates where (eg, home, neighborhood, community, or school) an individu- al spends time and engages in physical activity. 10,11 Social environmental factors, including seeing other adolescents performing physical activities 12 Alice Fang Yan, Assistant Professor, Joseph J. Zilber School of Public Health, University of Wisconsin-Milwaukee, Milwau- kee, WI. Carolyn C. Voorhees, Research Associate Professor, Kenneth H. Beck, Professor and Min Qi Wang, Professor, Maryland School of Public Health, College Park, MD. Correspondence Dr Yan; yanf@uwm.edu A Social Ecological Assessment of Physical Activity among Urban Adolescents Alice Fang Yan, MD, PhD; Carolyn C. Voorhees, MS, PhD; Kenneth H. Beck, PhD, FAAHB; Min Qi Wang, PhD, FAAHB Objectives: To examine the physical, social and temporal contexts of physical activity, as well as sex variations of the associations among 314 urban adoles- cents. Methods: Three-day physical ac- tivity recall measured contextual infor- mation of physical activities. Logistic regressions and generalized estimating equation models examined associations among physical activity types and con- texts, and sex differences. Results: Ac- tive transportation was the most com- mon physical activity. Home/neighbor- hood and school were the most common physical activity locations. School was the main location for organized physical activity. Boys spent more time on rec- reational physical activity, regardless of the social context, compared to girls. The average physical activity level was signiicantly lower for girls than for boys after school. Conclusions: Physical ac- tivity promotion interventions need to target physical activity environments and social contexts in a sex-speciic manner. Key words: social-ecological assess- ment; physical activity contexts; neigh- borhood environment; high school stu- dents; African American Am J Health Behav. 2014;38(3):379-391 DOI: http://dx.doi.org/10.5993/AJHB.38.3.7