In the last decade, world bodies have been advocating the importance of healthy ageing and the enabling role played by PA and built environments (e.g., [81]). As a result, the number of published articles on the associations between built environmental attributes and older adults’ PA increased over three times since the last systematic review in 2011 [15]. Moreover, there was a greater percentage of articles from outside of North America, with notable increases in research conducted in Asia and Europe, which expanded the range of examined geographical settings and cultures. We undertook a systematic review and applied a meta-analytic procedure to statistically identify built environmental attributes related to total PA and total walking, stratifying by measurement method.

In general, while the findings from Van Cauwenberg and colleagues’ systematic review published in 2011 were inconclusive [15], we found strong evidence of positive associations between walkability, access to destinations and services, personal safety from crime and PA. Also, while the relatively small number of articles included in Van Cauwenberg and colleagues’ review [15] precluded the examination of differences in findings by measurement method, this review and meta-analysis revealed important differences in associations when using objective versus perceived measures of environmental attributes and when using self-report versus objective measures of PA. These new findings and their implications are discussed in detail below.

Built environmental correlates of older adults’ PA

Walkability and access to destinations/services

We found strong to very strong evidence supporting the benefits of neighbourhood walkability on total PA and walking, regardless of measurement method. Two of the three components comprising walkability were found to individually relate to PA: strong evidence supported the association between access to destinations and services and total PA, for both objective and perceived environmental and PA measurement types. Evidence was also found supporting the impact of access to destinations and services and residential density on total walking, particularly when these attributes were measured objectively. Our findings highlight the importance of having local neighbourhood destinations for older adults to not only walk to and walk around, but to also engage in other types of PA. Furthermore, local destinations may provide a location for social activity and engagement, potentially reducing risk of social isolation and loneliness [82].

Although easier access to destinations and services tend to be highly correlated with greater residential density [83], our findings suggest that walking may be the only type of PA positively related to residential density. High levels of residential density may not be conducive to other forms of active transport, such as cycling. One study has found that Flemish older adults living in urban areas were less likely to cycle everyday than those living in semi-urban (i.e., less dense) areas [84]. While walking is the most popular type of PA that older adults participate in [9], cycling is also a popular PA mode in European countries such as the Netherlands, Denmark, and Germany, where cycling levels remain high even among older people [85]. Future research examining the differential influence of residential density on different types of PA as well as identifying the optimal threshold of density for supporting all types of PA will be important for informing planning policy and practice [86].

In terms of access to specific types of destinations in the neighbourhood, we found evidence supporting shops and commercial destinations, public transport, parks and public open space, and recreational facilities as possible facilitators of PA. No evidence was found for the seven other destination types examined. Overall, this is in line with the work of others who highlight that certain types of destinations may be more conducive to higher PA levels than other destination types [15, 27].

Shops/commercial destinations and public transport, particularly for objectively assessed measurement types, were positively associated with total walking and total PA, specifically self-reported measures of total PA. The importance of shops and commercial destinations for PA is consistent with findings highlighting that shopping is the most prevalent reason for older adults leaving their homes [87], and thus an important part of daily life. Therefore, ensuring neighbourhoods have ease of access to shops means that health-enhancing levels of PA can be incorporated into daily living. Availability and access to public transport not only facilitates PA levels but has the potential to also reduce car dependence [88] with co-benefits of environmental sustainability [89]. For older adults especially, access to public transport enables those who are not confident with driving or no longer able to drive to still travel outside of home, thus maintaining their mobility and reducing risk of loneliness [90].

We found strong to very strong evidence for parks and public open space and recreational facilities as correlates of total PA, particularly for self-reported types of measurement. This is consistent with findings in adults [91]. When comparing environmental measurement methods, evidence was found for positive associations between total PA and perceived, but not objectively assessed, access to parks, public open space and recreational facilities. Access to parks and public open space was also found to be positively associated with total walking. However, when comparing the environmental measurement type, it was the objectively assessed measures showing a positive association with total walking, not perceptions. Here, it should be noted that most of the objectively assessed positive findings were from studies based in Portland, USA [64, 92, 93], a city renowned for its walk-friendliness and management of parks in the presence of urban growth [94, 95]. Having accessible parks and public open space and recreational facilities in local areas may be beneficial beyond PA, as green spaces and visual cues of nature in parks may impart further psychological benefits on individuals [96, 97]. Moreover, both destinations provide an opportunity for fostering social connectedness/activities (e.g., a walk with friends in a park and a game of squash at a recreational facility).

Infrastructure and streetscape

Pedestrian-friendly infrastructure, particularly when measured objectively, was found to be positively associated with both total PA and total walking. This reflects qualitative [98] and experimental research [99] findings highlighting the importance of pavements/footpaths and other infrastructure, such as benches for resting, for older adults’ PA. Ensuring the provision of walk-friendly infrastructure, especially along routes to destinations within the neighbourhood, may be particularly pertinent. It is plausible that the relationship between walk-friendly infrastructure and PA may differ based on physical functionality. However, we identified only one study that had examined this, finding no difference in the associations [100].

We found evidence supporting a positive association between street lighting and total walking only. This highlights the importance of providing street lighting along pedestrian infrastructure so that its use is not dependent on the time of day. For older adults especially, ensuring neighbourhoods are well-lit at night may also contribute to a heightened sense of safety from crime [98]. This is because street lighting helps contribute to natural surveillance by allowing pedestrians to be seen.

We found no evidence of an association between pavement/footpath quality and PA. This is in contrast to qualitative research findings indicating quality of infrastructure to be particularly pertinent in facilitating PA among older adults [98, 99, 101]. Our findings may be explained by the diversity of measures used and/or lack of clear definition of pavement/footpath quality. For example, what constituted ‘footpath quality’ ranged from “curb quality” (objectively assessed) [47] to “quality and maintenance of sidewalks” (as perceived by study participants) [24].

Strong evidence supported the role of greenery and aesthetically pleasing scenery on levels of total PA (especially self-reported measurement types) and total walking. These findings are in line with recent research highlighting the importance of green, clean, and attractive neighbourhoods and streetscapes in facilitating PA [98, 102]. When stratifying by environmental measurement type, only perceived measures were found to be significant. Beyond facilitating PA, it is plausible that there are synergistic benefits of streetscape trees and vegetation, for example, in reducing urban heat island effect [103] and air pollution [104] – environmental factors linked with premature mortality [105] and global disease burden [106]. Following design principles of ‘tactical urbanism’, which are low cost interventions to make areas more attractive and pedestrian-friendly [107], environmental modifications such as planting trees and flora are micro-scale interventions that can be more easily implemented than macro-level interventions to street design and layout.

Safety

Safety from crime, especially when perceived measures were used, was found to be positively associated with total PA (primarily self-reported measures) and total walking. This adds to the evidence base as previous research in older adults has mostly shown inconsistent findings [31, 108]. Our findings are in line with the notion that perceptions of crime have more influence on behaviour (e.g., leaving the home) than objective crime rates [109]. This speaks in favour of interventions aimed at positively changing perceptions of safety (when appropriate) and encouraging older people to get out of home. This may be particularly important as the frequency of daily out of home trips is predictive of PA participation in this demographic [87].

Overall, we found no evidence to support the relationship between traffic-related safety and total PA and total walking. However, when only perceived measures of traffic safety were considered, there was evidence of a positive association with total walking only. It is possible that older adults may have no choice other than participating in walking near heavy neighbourhood traffic because they do not own a car and/or have limited access to public transport [73]. It may be that a substantial amount of walking and PA in older adults comes from actively travelling to and from destination-rich areas where traffic is typically heavy [27].

Differences in built environmental correlates by type of PA measurement method

We found more significant environmental correlates for self-reported PA than for objectively measured PA. One reason for this may relate to common method bias associated with self-reported PA and environmental attributes – systematic error variance introduced by measurement methods that do not accurately assess the constructs they represent and may be due to factors such as social desirability [110]. Another reason may be that the environmental attributes measured in these studies primarily influence walking behaviours that may be more easily measured by self-reports than by accelerometry. An additional reason may relate to issues with the accelerometry-based operationalisation of older adults’ MVPA. Sixteen of the 28 reviewed articles reporting objective PA findings used accelerometer cut-points and half of those applied an MVPA cut-point of 1952 accelerometer counts per min derived for adults [111]. As older adults have a lower MVPA cut-point due to lower resting metabolic rates [112], using the adult accelerometer cut-point likely resulted in lower estimates of MVPA, potentially masking associations. To accurately classify different intensities of older adults’ PA, future research using objectively assessed PA should be underpinned by appropriate cut-points.

Differences in built environmental correlates by type of environmental measurement method

Overall, there were numerous differences in the associations between built environmental attributes and total PA and walking, based on type of environmental measure. Attributes that can be classed within the functional (e.g., pedestrian infrastructure) and destination domains in Pikora’s framework tended to be significantly related to PA when objectively assessed [113]. In contrast, those attributes that fall within the safety and aesthetics domains were associated with PA when perceived measures were used. This may be explained by attributes within safety and aesthetics domains being more subjective in their interpretation and thus depend on perceptions that may vary greatly between individuals. Attributes related to function and destinations are more objective and, hence, are associated with lower levels of interpersonal differences in perceptions (e.g., a pavement is either present or it is not).

Effects were generally stronger for associations between the perceived environment and PA, which is consistent with previous research [114]. Unlike the objective environment, perceptions of the same neighbourhood environment can greatly differ across individuals due to differences in socio-demographics (e.g., socioeconomic status), preference, experience, culture and/or amount of walking in the neighbourhood [30]. Regular walkers may have more accurate perceptions of their local environments. Moreover, perceived measures often define neighbourhood in terms of time to reach a destination (e.g., 10–20 min’ walk from home) [40, 41], rather than set distances (e.g., objective 400 m home-centred buffers), and therefore may be more closely aligned with the individual and their own definition of ‘neighbourhood’.

Implications for future research and planning policy/practice

Socio-ecological models of health behaviour underpin the majority of research undertaken in the built environment and PA field. One of the key tenets of this approach is its emphasis on the importance of behaviour specificity [12], and for PA this means considering the domain in which PA was accrued. While taking a behavioural perspective allows for the pathways or mechanisms through which the built environment influences PA to be understood, it is possible that built environmental attributes may relate differently to different behaviours [115]. Instead, a public health perspective examining built environmental attributes associated with total PA focuses on the identifications of environmental attributes enabling health-enhancing levels of PA, which is accrued across all domains. Notably, nearly all built environmental correlates of older adults’ total PA were also identified as being environmental correlates of either active transport [27] and/or leisure-time PA [116], thus explaining the behavioural pathways through which the built form impacts on total levels of PA. There was one exception, however, with crime/personal safety being positively associated with total PA, but no evidence found for a relationship with either active transport [27] or leisure-time PA [116]. Other behavioural or psychosocial factors may explain the associations between crime/personal safety and total PA. Given the medium to strong evidence of these associations, it is especially important for future research to unpack the mechanisms through which crime/personal safety relates to total health-enhancing PA in order to better inform the implementation of suitable interventions. For example, a better understanding of fear of crime and assessment of the emotional rather than cognitive response to crime may be warranted [108]. Moderators of the relationship between safety and PA that warrant further consideration may include self-efficacy and physical functioning/capacity [117].

Research design issues

Longitudinal and quasi-experimental studies are needed to establish causal relationships between the built environment and PA. Insofar as possible, future research designs would also benefit from assessing and adjusting for residential self-selection to account for biases at the individual level (e.g., an older adult who enjoys PA or chooses to live near a park) and thus enabling, to a certain extent, the controlling of reverse causation. The findings of this review may help inform researchers involved with natural experiments on what environmental attributes to measure, given the environmental manipulation itself will be out of their control.

Better quality research may also come from conceptually-driven choices of built environmental attributes and validated PA measures. Where accelerometer cut-points and the classification of older adults’ PA intensities are concerned, it is important that the thresholds for moderate intensity activity are appropriate (e.g., 1013 counts per min [112]). Applying suggestions such as these also allows for the possibility of pooling data across countries. For example, there has been evidence of curvilinearity related to perceived access to destinations and services and objectively assessed MVPA in a multi-country study of adults [31]. This finding was only possible because of the use of comparable environmental exposure and PA outcome measures across a large range of diverse geographical locations combined with a high variability in exposures across countries (another issue that future research may care to address). Thus, the multi-country pooling of data based on valid, comparable measures are needed to address issues surrounding limited variability in environmental exposures and non-linear associations between exposures and PA outcomes. Other statistical analysis decisions such as adjusting for key socio-demographic covariates (i.e., age, sex, and education), and not categorising continuous environmental measures would contribute to improving the quality of future research designs.

Strengths and limitations of this review and meta-analysis

This systematic review and meta-analysis has several strengths. It addressed publication bias by including both peer-reviewed scientific articles and grey literature. It provided a quantitative synthesis of associations based on non-standardised environmental and PA measurement instruments and stratified findings by measurement types. It incorporated an extensive article quality assessment into the meta-analytical procedure and, therefore, adjusted the synthesis of evidence for study methodology quality. Limitations include: (1) not accounting for potentially correlated findings from the same article; (2) an inability to account for potential moderating effects of neighbourhood size and definition; (3) using a meta-analytic method that relied on statistical significance testing rather than effect size estimates and, thus, likely underestimating the evidence of environment-PA associations; and (4) including only articles published in English.