Brief report
Urban Trails and Physical Activity: A Natural Experiment

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Background

The built environment in which a person lives and works is thought to have a strong influence on his or her level of physical activity. However, this belief is largely based on cross-sectional studies underlining the need for prospective studies using natural experiments.

Design

This study adopted a quasi-experimental research design with multiple control neighborhoods and was conducted between 2005 and 2007. Data were analyzed in 2008.

Setting/participants

The subjects were children, adolescents, and adults in free-living conditions within one experimental and two control neighborhoods.

Intervention

An urban greenway/trail was retrofitted in a neighborhood that lacked connectivity of the residential pedestrian infrastructure to nonresidential destinations.

Main outcome measures

The main outcomes were 2-hour counts of directly observed physical activity in the general neighborhood and, at the school level, active transport to school.

Results

At the neighborhood level, the 2-hour counts of physical activity significantly increased between 2005 and 2007 (p=0.000) in the intervention neighborhood, with a median increase of 8.0 counts. The control neighborhoods had a significant decrease in counts (p=0.000). The pre- and post-intervention changes between experimental and control neighborhoods were significantly different for total physical activity (p=0.001); walking (p=0.001); and cycling (p=0.038). There was no noted change over time for active transport to school in either the intervention or control neighborhoods.

Conclusions

Changes to the pedestrian connectivity of the built environment infrastructure may lead to greater levels of physical activity. However, this positive effect was limited to physical activity at the neighborhood level and not to active transport to school.

Introduction

The built environment is thought to have a strong role in facilitating or hindering physical activity across multiple domains, including transportation and leisure-time physical activity. This belief is based largely on cross-sectional research that is limited by its inability to demonstrate causal relationships.1, 2 As such, “natural experiments” using quasi-experimental research designs have been identified as the top research priority in detecting causality between the built environment and physical activity.1, 3

In 2004, an opportunity to conduct a natural experiment presented itself in Knoxville TN to examine the impact of one aspect of the built environment, neighborhood connectivity, on physical activity. The specific intervention involved retrofitting a neighborhood with an urban greenway/trail to connect the pedestrian infrastructure with nearby retail establishments and schools. Construction of trails that encourage walking and other forms of physical activity has been shown to be associated with increased physical activity among sedentary individuals and with maintenance of physical activity among the currently active.4, 5, 6

A 6-month period between the announcement of the greenway/trail project and construction allowed investigators to implement a quasi-experimental research design with baseline (2005) and post-intervention (2007) assessments. Direct observation of physical activity was used to examine whether improvements in the built environment causes increases in physical activity, in both neighborhood and school settings, in the intervention and control neighborhoods. Direct observation of physical activity in public places provides contextually rich data and has been successfully used in built environment studies.7, 8, 9, 10, 11, 12

Section snippets

Methods

The study utilized a quasi-experimental multiple-control neighborhood research design to explore causal relationships between the built environment and physical activity.13 Specifically, the methodology was designed to detect changes in directly observed physical activity at the neighborhood level after exposure to an improved pedestrian infrastructure that enhanced connectivity to retail and school destinations. The research design was planned around the start of greenway/trail construction

Results

Figure 1 presents the 2-hour physical activity counts observed in the experimental and control neighborhoods. At baseline (2005), there was no significant relationship between the 2-hour total physical activity counts in the experimental and control neighborhoods (p=0.370). Focusing on pedestrian- and cycling-specific physical activity yielded similar findings (p=0.176 for walkers, p=0.060 for cyclists). However, at follow-up (2007), the 2-hour count of total physical activity was significantly

Discussion

The current study confirms that enhancing a neighborhood's pedestrian infrastructure increases outdoor physical activity. However, the positive increase detected in the current study was limited to physical activity observed in the general neighborhood and did not extend to the school environment. Previous cross-sectional research on walking and ATS can provide some insight into these findings.

Walking for transport is positively related to neighborhood density, resident proximity to

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