Built environment and lower extremity physical performance: prospective findings from the study of osteoporotic fractures in women.

The role of neighborhood in determining health outcomes among older adults has been examined in a growing number of studies over the past decade (Yen, Michael, & Perdue, 2009). A recent review of this literature from 1997–2007 reported consistent evidence in support of an association between built environment and amount of walking, but highlighted limitations – cross-sectional studies and the failure to specify theory or use direct measures of neighborhood features – and identified the need for additional research to determine if neighborhood design is associated with (downstream) health outcomes, such as disability, via physical activity behavior (Yen, et al., 2009). In 2005, Clarke and George proposed a model of the ‘disablement pathway’ in which the built environment exacerbates or narrows the gap between an individual’s physical performance and the physical demands of a given activity (Philippa Clarke & George, 2005). The term ‘built environment’ is an umbrella term that encompasses three integral urban planning concepts: urban design, land use, and transportation systems (Handy, Boarnet, Ewing, & Killingsworth, 2002). Recent articles have begun to evaluate the role of built environment characteristics in the disablement process (Beard et al., 2009; Bowling & Stafford, 2007; Brown et al., 2008; P. Clarke, Aishire, Bader, Morenhoff, & House, 2008; P. Clarke, Aishire, & Lantz, 2009; Freedman, Grafova, Schoeni, & Rogowski, 2008). however, all of these studies except two (Brown, et al., 2008; P. Clarke, et al., 2009) were cross-sectional. In addition, all of these studies except one (Brown, et al., 2008) used self-reported measures of physical function. Performance-based measures have been shown to add important information in the assessment of older adults (Myers, Holliday, Harvey, & Hutchinson, 1993), to identify functional problems that the individual or family may not have reported (Curb et al., 2006), and are strong predictors of outcomes such as disability, frailty, and mortality (Ferrucci et al., 2004). No previous studies included walking behavior, the proposed mechanism linking built environment and physical performance, in their analysis. Finally, most of these studies lacked an explicit theoretical framework to guide determination of which neighborhood factors may impact mobility. Travel behavior theory proposes that the demand for travel is related to the demand for activities. It has been assumed that people will choose to minimize time and cost of travel if given a choice (Cunningham & Michael, 2004). Travel behavior theory predicts a link between transportation infrastructure and pedestrian behavior (Cervero & Kockelman, 1997). Transportation systems include the street network within a region and influence how easy it is to travel through a neighborhood and get to places a person wants to go. A street network that is “highly connected” has many possible routes between destinations making trips more direct. Further, small blocks shorten the distance people have to travel to a desired destination. Empirical research is equivocal but generally confirms that areas characterized by a highly connected street network encourage walking, meaning that a greater number of trips to desired destinations are accomplished by foot rather than by motorized transportation (Berrigan, Pickle, & Dill, 2010; Hess, Moudon, Snyder, & Stanilov, 1999). Better street connectivity (i.e., streets leading to other streets, rather than ending in cul-de-sacs that are more common in newer developments) is associated with more walking among the general population (Saelens, Sallis, & Frank, 2003) and in older adults (F. Li, Fisher, Brownson, & Bosworth, 2005; Saelens & Papadopoulos, 2008). Other studies reported no association (Nagel, Carlson, Bosworth, & Michael, 2008; Satariano et al., 2010). Street density is the strongest predictor of non-motorized travel; smaller block size is a proxy for higher density and greater walkability (Cervero & Kockelman, 1997; Hess, et al., 1999). Shorter blocks mean more intersections and, therefore, shorter travel distances and a greater number of routes between locations (Cervero & Kockelman, 1997). Neighborhoods with small blocks and continuous sidewalks had three times the amount of walking compared to neighborhoods with large blocks and incomplete sidewalks (Hess, et al., 1999). To address the limitations of these earlier studies, we used longitudinal data from a cohort study of older women to assess the association between the walkability of the built environment, specifically street connectivity and street density, and changes in walking and lower extremity physical performance.