Erica Frost Finsness
Project title: Association Between Neighborhood Walkability and Physical Performance Function in Older Adults
Completed in: 2008 | Faculty advisor: William E. Daniell
Significance: The built environment has become an area of recent interest in public health. Neighborhood walkability is one way to meaningfully quantify the potential impact of a built environment on health behaviors, specifically walking. Exercise, including walking, is positively associated with physical function in older adults. Physical function is critical in retaining fuunctional independence and is also predictive of disability and short-term mortality.
Background: This study investigated whether more walkable neighborhoods were associated with improved lower-extremity function (LEF) in older adults, and relied on data collected for two independent studies. The Walkable and Bikable Communities (WBC) study was undertaken by the UW Health Promotion Research Center and used telephone surveys and objective environmental measures to determine probability of walking in areas of urbanized King County. The Adult Changes in Thought (ACT) study is a prospective, longitudinal study of risk factors for dementia in older adults (age > 65), undertaken at Group Health Cooperative in Seattle. Participants in the ACT study underwent examinations of cognitive and physical function every two years.
Methods: This cross-sectional study used WBC and ACT data. A previous researcher used GIS to link ACT and WBC data. Mean walkability was calculated fr radii of 100 m, 500 m and 1000 m around each subject's residence and linked to health data. The 500 m average walkability value was used as the exposure variable, and corresponds to a 10 minute walk at a rate expected for older adults. Walkability was categorized based on quartiles. The primary outcome was LEF, measured by tests of walk speed, balance and lower limb strength. Analyses were stratified on gender. Multiple linear regression was used to assess the relationship between walkability score and LEF, while controlling for covariates. Secondary analyses looked for association between walkability (log-transformed or dichotomized) and LEF, or the individual performance tests.
Results:The study included 740 subjects (468 women, 272 men), who had lived for at least two years at a residence within the study area. The mean age was 77.7 (SD 5.9) for men and 78.4 (SD 6.1) for women. Mean LEF for men was 9.1 (SD 2.8) and 8.1 for women (SD 3.1). Walkability scores within radii of 100 m and 1000 m were significantly and strongle correlated with scores within 500 m radii (person correlation>0.96, p<0.001). LEF was significantly and strongly associated with each of the physical performance tests (Gamma>0.53, p<0.001). In unadjusted analyses, walkability showed no association with LEF. The multiple linear regression model explained about a quarter of the variation in LEF (R-squared=0.28 for men, 0.22 for women), but again there was no significant association between walkability and LEF. Secondary analyses showed qualitatively similar results.
Conclusions: No association was found between walkability and LEF. There are many possible explanations for not finding an association between walkability and LEF, even though an association might truly exist. Improvements in the study design, such as using other measures of walkability and physical performance, would be useful in assessing this possibility. Other possible improvements in study design include use of longitudinal data and collection of information on beliefs and behaviors.