Recreational infrastructure (play areas) for children can be classified as private (provided by their parents in and around the home), public (community areas or schools) or private-public (commercial play areas). Private recreational infrastructure may be subject to regulations associated with the property and issues of flexibility of use based on tenure of ownership (e.g., renter or home-owner). Public recreational infrastructure is primarily the responsibility of the municipality or agency charged with the provision of the original infrastructure, as is the maintenance and continued monitoring of the safety and condition of such assets. School yards, playgrounds and open space parks are most often considered public recreational infrastructure. Private-public recreational infrastructure includes youth camps, commercial clubs, and other businesses providing places for children to participate in physical activity. All of these recreational infrastructures are subject to land use regulations, including zoning codes. Twenty one studies that were reviewed examined the relationship between recreational infrastructure and children's physical activity [16–36]. The overwhelming majority (i.e., 19) of studies used a cross sectional design. One study used a 1-year longitudinal design and one used an intervention design. Five of the 21 studies used an objective measure of physical activity, including either accelerometry or heart rate monitoring, four used direct observation, 13 used a self-report measure, and one study used both objective and self-report measures. Seven studies used an objective measure of the environment (generally based on Geographic Information Systems), 12 used a self-report measure, and two studies used both methodologies. Finally, 12 of the studies were conducted in the US with the remaining studies being conducted in countries including Canada, England, Australia and Portugal.
Private recreational infrastructure
Four out of six studies found no association between home equipment and children's physical activity. Specifically, Sallis et al.  found no association between an objective assessment of equipment available in the home and observed levels of physical activity among preschool children. Dunton et al. and Trost et al.  found no association between adolescents' reports of equipment in the home and their self-reported physical activity. A second study by Trost et al. found no association between adolescents' reports of home equipment and their objectively measured physical activity using accelerometers. In contrast, Fein and colleagues  and Stucky-Ropp and DiLorenzo  found that the number pieces of exercise equipment in the home was positively and significantly associated with higher self-reported physical activity among adolescents girls and boys and young adolescent girls (but not boys).
Differences in the results outlined above cannot be explained by differences in sample size, participant age, or the operationalization of home equipment. Differences, however, may be explained by differences in the ethnic composition of the samples; both studies identifying a significant effect for home equipment used a predominantly white sample, whereas, studies that did not identify an effect used either an exclusively African American sample  or samples of mixed racial/ethnic background [3, 19, 22]. It should also be noted that both studies identifying a significant positive effect used a self-report measure of physical activity. The remaining studies used self-report [19, 25] or an objective assessment [22, 26] of physical activity. Thus, any association identified between home equipment and children's physical activity is limited to white adolescent samples and to self-report measures of physical activity.
Public recreational infrastructure
Proximity of parks and playgrounds
A significant positive association between the proximity of parks and playgrounds to the home and children's physical activity was identified in three out of five studies. In an exclusively Hispanic sample, Gomez et al found that objectively measured distance to the nearest play area was inversely associated with adolescent boys', but not girls', self-reported physical activity. Sallis et al.  found that parents' reports of the number of play areas within walking distance of the home were positively associated with observed levels of physical activity among preschool children. Furthermore, Timperio, et al.  found that children who reported a lack of parks or sports grounds near their home made fewer walking and cycling trips. In contrast to these studies, Sallis et al.  and Adkins et al.  (using an exclusively Black sample) found no association between proximity of playgrounds and parks and children's objectively measured physical activity.
Although a number of ethnic/racial groups were assessed across studies, no consistent ethnic/racial differences were identified. Differences in methods used to assess physical activity, however, were noted for studies that did and did not identify a significant association. Both studies that found no association [16, 28] assessed physical activity using accelerometers, which provide an aggregate measure of physical activity across a number of days. In contrast, studies that found a significant association relied on self-reported or observed physical activity, both of which are prone to reporter/observer bias, but which can be tailored to provide a specific measure of physical activity (e.g., walking or cycling trips).
Availability of recreation areas and spending on recreational infrastructure
In eight out of ten studies, a significant positive association was identified between the availability of recreation areas, or the presence of such areas in the vicinity of the home, and children's physical activity. Among Australian samples, Timperio et al.  found that parents' reports of few sporting arenas in the area were linked with lower rates of walking and cycling among girls and Carver et al.  found that parents' reports of the presence of good sporting facilities nearby for their children were associated with higher self-reported walking or cycling among adolescent girls and boys (A simplified summary of the results from Carver et. al are presented throughout this review given the extensive number of variables assessed. Only results for the frequency of walking/cycling in general are reported). In a study combining qualitative and quantitative methods, Hume et al.  found that, when children were instructed to draw pictures of their home and their neighborhood, girls who drew more opportunities for physical activity, including recreational facilities such as gyms and swimming centers, had higher objectively measured physical activity. Among US samples, Zakarian et al.  found that a greater number of facilities for sport and exercise in the area (based on self report) were associated with higher adolescent self-reported vigorous activity and Brodersen et al.  found that the number of sport pitches in the borough, as determined by objective assessment, was associated with higher self-reported vigorous activity among girls but not boys. Similarly, Norman et. al.  found that objective measures of the number of recreational facilities and parks within a mile of the home were associated with higher objectively measured physical activity among adolescent girls, but not boys. Finally, Mota et al.  and Fein et al. using samples from Portugal and Canada respectively, found that adolescents' reports of the availability of facilities such as swimming pools, playgrounds and parks were associated with higher self-reported physical activity. In contrast to the aforementioned studies, Dunton et al.  found no association between girls' reports of activity-related resources in the community and their self-reported physical activity and Sallis et al.  found no association between access to facilities and children's objectively measured physical activity. In addition, no association was identified between spending on recreational infrastructure and children's self-reported physical activity .
With one exception, there are no obvious differences in the designs of studies that did and did not identify a significant association between the availability of recreational areas and children's physical activity. Specifically, there were no clear differences across studies in the definition of recreational facilities (which usually included structures such as swimming pools, gyms, sporting arenas, and parks), the methods used to assess physical activity, or the demographic characteristics of the samples. There were, however, clear differences is sample size across studies. The majority of studies that identified a significant effect used samples of 1000 or more participants. In contrast, the two studies that found no effect used samples of approximately 100 participants, taking age and gender break-downs into consideration. This suggests that the association between the availability of facilities and physical activity among youth is relatively small and therefore only measurable with a large sample. While the availability of facilities was assessed in all studies, no studies directly asked children or parents whether they used such facilities. Consequently, the association between recreational facilities and physical activity is indirect at best.
Three out of three studies identified a negative association between distance to school and children's physical activity. Timperio et al. and Cohen et.al.  (girls only) found significant negative associations between an objective measure of distance to school and children and adolescents' objectively measured moderate to vigorous physical activity. Ewing et al.  found that lower walk/cycle time to school, an indirect measure of distance, was associated with higher rates of active commuting to school. In contrast to studies assessing distance to school, Braza et al.  and Ewing et al.  found no association between school size, an indirect measure of whether or the school is located in a residential area and therefore close to homes, and the rates of walking and cycling to school.
With respect to characteristics within schools, Sallis et al.  found that middle-school-aged children were more likely to be active during school recess periods when there was a larger number of activity-related equipment (e.g., balls) and the permanent activity structures (e.g., basketball hoops) available; these effects were most notable in the presence of adult supervision. Similarly, Fein et al.  found that adolescents' reports of the availability of sports equipment, the functionability of equipment, and access to athletic facilities at school were associated with higher self-reported physical activity. In contrast, Zask et al.  found no association between the availability of playground equipment (with the exception of balls) and children's physical activity. Finally, in an intervention examining the effect of playground markings such as hopscotch and court lines for basketball on children's physical activity, Stratton and Mullan  found significant increases in moderate to vigorous physical activity and vigorous physical activity in intervention schools relative to control schools.
In sum, three out of three studies found that children who live close to schools are more likely to actively commute to school and three out of four studies found that children were more active during play periods when characteristics of school play areas (e.g., access to equipment, permanent play structures, and marked courts) facilitated physical activity. No associations, however, were found between school size and children's physical activity. The lack of effects of school size reported by Braza et al.  and Ewing et al.  may be attributable to the use of aggregate data, or data collected at one level (e.g., a census track) that is then aggregated to a higher level (e.g., county). As a result of the process of aggregation, any information pertaining to individual residences or specific locations is lost.
Two types of transport infrastructure were examined in studies including the provision of amenities (e.g., sidewalks, crossings) and the presence of road hazards. Transportation infrastructure in urban areas is the responsibility of a number of agencies. For example, in the United States, Metropolitan Planning Organization (MPO) are generally charged with the preparation of planning documents and the allocation of funding for major programs and projects, whereas, the designation of crosswalks, traffic signals, pedestrian signage, and other amenities are in general the responsibility of various transportation departments based on right-of-way and public ownership of property. Nine studies assessed associations between transport infrastructure and children's physical activity [18, 24, 30, 32, 33, 36, 37, 39, 40]. All nine studies used a cross sectional design. Two studies used an objective measure of physical activity and six studies used an objective measure of the environment. The remaining studies relied on self-report instruments. Five of the nine studies were conducted in the US; the remaining studies were conducted in Australia and Portugal.
Provision of amenities
Presence and condition of sidewalks and bike lanes
Results generally supported a positive association between the presence and condition of sidewalks and children's physical activity with three out of four studies identifying a significant positive effect. Ewing et al.  found that the proportion of street miles with sidewalks was positively associated with children's rates of walking or cycling to school. In an evaluation of the implementation of a Safe Routes to School program, Boarnet et al.  found that children who passed areas in which sidewalks were installed were more likely to walk or cycle to school than children who did not pass such areas. In contrast, Mota et al.  found no association between the perceived presence of sidewalks on streets in the neighborhood and adolescents' self-reported activity. In the only study that assessed the impact of sidewalk conditions, Jago and colleagues  found that objectively assessed sidewalk characteristics such as the distance from the sidewalk to the curb, average height of trees, and sidewalk material and type were associated with higher objectively measured light intensity physical activity (e.g., slow walking) among children. The studies that identified significant effects used objective measures of the environment and measured children's walking (or low intensity physical activity) as the outcome variable, which is the most likely component of physical to be influenced by sidewalk characteristics. In the only study that failed to identify a significant effect, a self report measure of sidewalk availability was used along with a generalized measure of physical activity that may not reflect subtle differences in physical activity that result from the presence of sidewalks.
With respect to infrastructure for cycling, Jago et al.  found no association between the ease of cycling (presence of bike lanes, attractiveness for cycling, number of read lanes) and objectively measured light intensity physical activity in a sample of boys and Ewing et al.  found no association between the presence of bike lanes and children's walking/cycling to school. Furthermore, Carver et al.  found that the perceived ease of cycling was associated with lower (rather than higher) rates of cycling among boys. Spurious findings for the presence of bike lanes or ease of cycling may be explained by a number of factors including the use of a measure of physical activity that cannot detect cycling (i.e., accelerometers) , low rates of bicycling to school in general , and inflated type II error due to performing an extensive number of analyses .
Presence of controlled crossings, street connectivity, and access to destinations
Two studies examined the association between the presence of controlled crossings (e.g., presence of lights, crossings, or crosswalks) and children's physical activity, both of which identified significant positive effects. Timperio et al.  found that parents' reports of a lack of traffic lights and controlled crossings were associated with lower rates of walking and cycling among boys, but not girls. In their evaluation of a Safe Routes to School program, Boarnet, et al.  found that children who passed areas in which traffic control methods were installed were more likely to walk or cycle to school than children who did not pass such areas.
Conflicting results were found for studies assessing street connectivity with only two out of four studies identifying a significant effect in the anticipated direction. Braza et al.  found that an objective measure of street connectivity was associated with higher rates of walking or biking to school. Similarly, Norman et al. found that higher intersection density (also assessed using an objective measure) was associated with higher objectively measured moderate-to-vigorous physical activity among girls but not boys. Mota et al. , however, found no associations between perceived street connectivity and adolescents' self-reported activity. In contrast to what might be expected, Timperio et al.  found that a more direct route to school (i.e., higher connectivity, which was assessed using objective methods), was associated with lower rates of walking and cycling to school among older children (10–12 years); no links were found between connectivity and active commuting to school among younger children (5–6 years of age).
The difference in findings reported by Mota et al. versus Braza et al. and Norman et al. may reflect the possibility that effects of connectivity are only observed when objective measures of connectivity are used; it is possible that individuals are not able to accurately recall and report the level of street connectivity in their neighborhood. The findings outlined by Timperio et al., which were opposite to those expected (with higher connectivity or a more direct route associated with lower rates of active commuting to school), are more difficult to explain. Timperio et al. suggest that the counterintuitive effects of connectivity in their study may reflect the possibility that children's travel behavior is more influenced by traffic safety concerns than street networks.
Three out of four studies identified a significant positive association between access to destinations and children's physical activity. This consistent pattern was noted although a variety of measures of access were used across studies including the presence of destinations such as shops, access to public transportation, and retail floor area ratio (i.e., ratio of retail building square footage to parcel square footage). Timperio et al.  found that parents' reports of a lack of public transportation were associated with lower rates of walking and cycling among girls but not boys. Mota et al.  found that the ability to walk to destinations such as shops and transit stops was associated with higher physical activity among adolescents and Norman et. al. found that a greater retail floor area ratio (reflecting greater retail space and access to shops) was associated with higher objectively measured moderate to vigorous physical activity among adolescent boys but not girls. In contrast to expectations, Carver et al.  found that adolescent girls' reports of greater access to convenience stores reported lower, rather than higher, rates of walking for transport. The general consistency of results for access to destinations, despite differences in its operationalization, suggests that it should be considered further in future investigations.
A variety of road hazards have been examined across studies including the number of roads to cross, the presence of a road barrier, traffic speed and density, pedestrian and cyclist safety, and terrain. All three studies assessing road hazards found a negative association between such hazards and children's physical activity. Timperio et al.  found that parents' reports that their children had to cross many roads to get to a play area (girls and boys) and of high levels of traffic density in their local area (boys only) were associated with lower rates of walking and cycling among children. In a second study by Timperio et. al. , using the same sample but using an objective assessment of the environment, the presence of a busy road barrier (e.g., a highway) en route to school (5–6 years olds and 10–12 year olds) and the presence of a steep incline (5–6 year olds only) were associated with lower rates of active commuting to school. Similarly, Carver et al.  found that parents' reports of traffic impeding the ability to walk were associated with lower rates of walking or cycling among girls and boys, whereas, parents' perception of the roads in the area being safe was associated with a higher frequency of walking among girls (but not boys). It is worth noting that all of these studies were conducted with urban Australian samples.
Both recreational and transport infrastructures exist within the context of local community conditions. The actions of other community members and agencies such as police patrols, community clean-up programs, and/or transient populations, all exert influence at the local level. These conditions include both positive and negative environmental attributes such as general neighborhood safety, safety of play areas, crime rates, social disorder and stranger danger, physical disorder and weather conditions. Eighteen studies were identified that assessed links between local conditions and children's physical activity [16–18, 21, 24, 27, 28, 30, 32, 40–48]. All but one study used a cross sectional design. Four studies used an objective measure of physical activity (accelerometry), one used direct observation, and fifteen studies relied on a self-report measure of physical activity. With regard to measures of the environment, nine studies used a self-report measure, seven studies used an objective measure and two studies used both methods. The vast majority of studies (13 out of 18) were conducted in the US.
Safety and neighborhood disorder
Safety, crime, and area deprivation
Nine studies examined the association between perceived safety and children's physical activity. These studies overwhelming reported a null effect with seven [16, 27, 28, 32, 45, 48] of the nine studies showing no association between perceived safety and children's physical activity. The lack of an association was not limited to a particular research design or sample population. Two exceptions to the pattern of null findings are the studies by Molnar, et al.  and Gomez et al. . In Molnar et al. residents' reports of the safety of children's local play areas were positively associated with parents' reports of their children's participation in recreational physical activity. Similarly, Gomez et al.  noted that adolescents' reports of perceived neighborhood safety were associated with higher self-reported outdoor physical activity for girls but not boys. The general lack of findings for perceived safety may reflect the fact that most of the studies measured general levels of physical activity, which may or may not be linked with neighborhood safety given that children can be active outside their neighborhood.
In contrast to perceived safety, three out of three studies identified a significant negative association between crime or area deprivation and children's physical activity. Gordon-Larsen et al.  and Gomez et al.  (girls only) found significant inverse associations between objectively measured crime rates and adolescents' self-reported physical activity. Similarly, Brodersen et al.  found that area deprivation (i.e., rates of car ownership, housing tenure, unemployment and overcrowding in the district) was associated with lower self-reported physical activity among 11–12 year old girls but not boys. Finally, Carver et al.  found that the presence of roaming dogs were associated with lower rates of walking or cycling among adolescents.
Social and physical disorder and neighborhood aesthetics
Three studies assessed links between neighborhood disorder and children's physical activity. Findings were mixed across these studies, likely reflecting differences in the operationalization of disorder. Molnar  objectively measured physical (e.g., graffiti, empty beer bottles) and social (e.g., alcohol in public, people selling drugs) disorder using coded video recordings and direct observation of neighborhoods. Both forms of disorder were associated with lower levels of parent-reported recreational activity among adolescents. Jago et al. , however, found no association between an objective measure of neighborhood tidiness and children's objectively measured physical activity. Likewise, Timperio et al.  found no association between children's perceptions of stranger danger (a source of social disorder) and parents' reports of their walking and cycling to destinations. Thus, it appears that any association between neighborhood disorder and physical activity may be limited to much higher levels of disorder (or deviance) such as those measured by Molnar et al. A general lack of tidiness or the perception that strangers can be dangerous but may not be enough to dissuade youth from being active outdoors. In the only study that assessed perceived aesthetics, Mota et al.  found that adolescents' reports of the aesthetics of their neighborhoods (i.e., there are many interesting things to look at while walking) were positively associated with their self-reported physical activity.
Region and weather
A significant association between weather and children's physical activity was identified in two out of five studies. Baranowski et al.  and Brodersen et al.  found that preschool children and 11–12-year-old boys respectively were less active during hotter months of the year. Brodersen et al.  also found that higher rainfall was associated with lower self-reported physical activity among girls but not boys. Although "unsuitable" weather was reported by adolescents as a perceived barrier to physical activity in the study by Tappe et al. , such perceptions were not associated with lower levels of self-reported physical activity. Similarly, Gordon-Larsen et al.  found no relationship between the month of the year and adolescents' self-reported physical activity, indicating a lack of a seasonality effect. Finally, Sirard et al.  found no association between weather conditions and rates of walking and biking to school.
The effects of weather may have been underestimated in these studies due to the restricted time range in which the data were collected. For example, Gordon-Larsen et al.  used data collected on physical activity between April and December. It is possible that the effect of bad or unsuitable weather was eliminated by the exclusion of the months of January through March (winter months in the northern hemisphere where the research was conducted). There was also limited variability in the geographic region within each study. No studies collected data across multiple regions that varied in the suitability of the climate for outdoor activity. Consequently, inconsistent or non-significant effects could be explained by a general lack of variability in the data by month of the year and/or location. Furthermore, no studies considered the availability of resources for indoor recreational activity in communities. It is likely the unsuitable weather conditions will most often be associated with low levels of physical activity in communities in which there are few opportunities for indoor physical activity.
Region, urban/rural location, and population density
Three studies examined associations between region and children's physical activity, with one of the three studies showing a significant effect. Gordon-Larsen et al.  found that residence in the Northeast of the United States was associated with higher self-reported physical activity among adolescents in comparison to residence in the South, West or Midwest. This effect of region could be explained by a myriad of factors such as regional differences in weather, income, education, ethnic/racial make-up, and access to community resources. When examining rural/suburban versus urban location, Sirard et al.  found no differences in rates of walking and biking to school for schools located in urban and suburban areas. Felton et al.  found mixed results for location. White girls in urban areas were more active (based on self-reports) than White girls in rural areas. The opposite was found for Black girls; black girls living in rural areas were more active than Black girls from urban areas. Although the difference was not discussed by the authors, it is possible that White girls from urban areas lived in neighborhoods in which they could take advantage of the infrastructure for physical activity generally attributed to urban areas such as the presence of sidewalks and accessible parks. While Black girls may also have had access to similar resources, their ability to use such resources may have been limited by neighborhood characteristics such as crime.
Two studies assessed links between population density and children's active commuting to school; no consistent effects were identified. Ewing et al.  and found no association between population density in the immediate area around children's homes and their rates of walking/cycling to school. In contrast, Braza et al.  found that higher population density was associated with higher rates of active commuting to school. Neither study considered whether children attended their local school, rather than a magnet or private school outside of the local area, or the feasibility of children walking or riding to school.