In the present study, direct associations between GIS-derived physical–environmental factors and self-reported physical activity were detected at the individual level among high school girls. An association was found between VPA in 12th-grade girls and several physical activity resources, including churches, parks, and individual and multipurpose commercial facilities. In addition, the number of colleges was associated with total METs. When all physical activity resources were combined in a single model, total commercial facilities remained significantly associated with number of 30-minute blocks of VPA. The availability of parks was significantly associated with total METs for white adolescent girls. These findings are consistent with the premises of the social–ecologic model for physical activity, which proposes that the physical environment exerts an influence on the physical activity behaviors of individuals.7,23
Vigorous physical activity was significantly related to the number of commercial facilities within the 0.75-mile street-network buffer in both the facility-specific and combined facility analyses in this study. Activities performed in facilities such as dance studios, recreation centers, and tennis courts are often of vigorous intensity. Others studies have found positive relationships between commercial facilities and physical activity in girls, most notably Norman et al.,24
who found that the number of private recreational facilities was associated with MVPA as measured by accelerometry in girls aged 11–15. The relationship between the number of facilities and physical activity also was supported in work completed by Gordon-Larsen and colleagues,25
although in their study the operational definition of facilities included not only commercial facilities but also schools and parks.
This study also confirms previous research that shows a relationship between the number of available parks nearby and physical activity in adolescent girls.26
In the facility-specific analyses, the number of parks was associated with the number of blocks of VPA. In the combined facility analysis, parks were associated with total METs in white girls only. For each park within the 0.75-mile street-network buffer of a white girl's home, there was an increase in total METs. Racial differences in the use of parks have been reported previously in the adult literature.27
Racial differences seen in this study also may be a function of differential access to and subsequent use of quality parks, safe parks, or both. It should be noted that other studies have failed to find an association between physical activity and the number of nearby parks in all-boy samples28
and in multivariate models of girls.24
In addition, one study found that the distance to the nearest park was significantly associated with physical activity in boys but not girls in inner-city youth.29
Given these contradictory studies, further research is needed to explore additional factors (i.e., quality and safety of parks) that may explain the differential results across racial and gender subgroups.
After adjusting for race, BMI, SES, and median household income, there was a significant relationship between churches and VPA. Many churches have physical activity teams and facilities such as gyms or outdoor basketball goals, or they provide open spaces in which to be active. This is the first study to examine objective measures of the number of churches nearby and physical activity. White girls reported more activity than African-American girls, but more African-American girls had a church near their homes, and they attended church more often than white girls.30
In a study of adult, church-going African-American women, physical activity programs at a woman's church were significantly associated with meeting MVPA recommendations.31
Churches could serve as sites for interventions designed to help African-American adolescent girls become more active, as was attempted in Go Girls!, a church-based nutrition and physical activity program designed for African-American girls.32
Finally, the number of colleges nearby was significantly associated with total METs. We cannot determine from this study why proximity to college campuses was associated with increased METs for this population. College campuses may offer increased access to physical activity facilities, may be located in areas of high walkability or mixed land use, or may provide for differential social norms for physical activity. They also may provide open spaces for physical activity or offer lessons and programs in sports, dance, or other types of physical activity for children and youth. Future studies should examine these possibilities.
To date, this study is one of the most comprehensive investigations that has examined, at the individual level, the association between physical activity and objectively measured physical activity resources in adolescent girls. The study is particularly interesting because it focuses on adolescents who are in transition from childhood and dependence on parents for decision-making and resources to young adulthood and the increased independence of college or employment. The study included a wide range of neighborhood facilities that have particular importance as physical activity resources in this age group, as well as physical activity resources that have not been considered previously (e.g., churches). In addition, the study found that certain types of physical activity resources may be associated with VPA. These include individual and multipurpose commercial facilities, parks, and churches.
This study was unique because it examined the association of physical activity with a wide range of community resources, including schools and churches, where girls can be physically active. The study had a number of strengths, including the diverse sample and the diverse geographic areas studied. The study included nearly equal numbers of white and African-American adolescent females, allowing for tests of interactions across race. The study area encompassed 13 counties, with widely varied levels of access to physical activity resources. Previous studies have cited limited geographic variability as a shortcoming.24
The findings of the study should be interpreted in light of the following limitations. First, the study examined the availability of physical activity facilities rather than the actual use of facilities by study participants. Further, the study could not categorize facilities as safe, high quality, attractive to girls, or affordable, characteristics that may be important predictors of use. Second, physical activity was measured by a self-report instrument, which may be subject to response bias; however, the instrument has been validated against accelerometry in adolescent girls.20
Third, multiple statistical tests were performed, and a small percentage of the observed significant associations may have been due to chance. Fourth, the study population was not selected at random. Finally, the study included only adolescent girls, and therefore conclusions about boys or other age groups are not possible.
In the present study, correlations between physical activity resources and nonwork physical activity were significant but small in magnitude. This is consistent with previous research that has reported that the physical environment per se, either perceived or objectively measured, consistently explains a significant but small (usually <5%) portion of the variance in physical activity among adolescents.7,24,33,34
Nevertheless, these relationships are likely to influence health outcomes linked to physical activity because the physical environment affects all individuals in a population over extended periods of time. Studies assessing the temporal and causal relationships between the physical environment (and its changes) and health-related outcomes are an important next step in this research.