What is the impact of the built environment on leisure moderate-to-vigorous physical activity and sedentary time among the elderly: A cross-sectional study

Although many studies have reported the association between moderate-to-vigorous physical activity (MVPA), sedentary time (ST), and the built environment (BE) among older adults, little is known about these associations in the Chinese older adult population. The purpose of this study was to investigate how various factors in the built environment of Nanjing’s communities influence leisure moderate-to-vigorous physical activity and sedentary time among the elderly. A multilevel cross-sectional study was conducted from November 2016 to April 2017. Altogether, thirty neighborhoods were selected and 586 individuals aged 60 years or older living in the urban zone of NanJing in Southern China were surveyed. Physical activity was measured using Actigraph GT3 Accelerometer. Built environment variables were measured using ArcGIS software. A multivariate linear regression method was used to analyze the factors influencing leisure moderate-to-vigorous physical activity and sedentary time among the elderly.

Our findings provide support for the association between the built environment and physical activity among the Chinese elderly. Some characteristics of the built environment including land-use mix and distance to fitness venue may affect MVPA, while other characteristics including population density and land-use mix may impact ST. In formulating urban planning policies, the above factors should be taken into account to promote physical activity in older people, encouraging them to modify their sedentary lifestyle and improving their overall health.

Background
The increasing aging of the population and resulting social and economic pressures have become a great challenge for Chinese society today and for a long time to come. Data from the 2010 National Census showed that China's population aged 60 and over represented 13.2% of the total population, with 119 million people aged 65 and over representing about 8.9% of the total population. China has 21 provinces with a predominant elderly population. China has also become the world's largest elderly population, representing 21.04% of the total elderly population. The United Nations predicted that by 2049, China's elderly population over 60 years of age will represent 31% of the total world's population, second only to the one in Europe.
With the rapid rise of urbanization in China, the living environment for the elderly has been facing unprecedented challenges, such as high population density, serious shortage of public facilities, and limited transportation of living space, which are extremely detrimental to physical activities in the elderly. The classical social ecological theory holds that physical activity in the elderly is influenced by variables such as internal and interpersonal factors, the physical environment, and policy, and that the impact of intervention is optimal when all these factors are 5 combined. The physical environment is defined as the surrounding living environment available to the elderly for physical activity, leading to the tenet that leisure physical activity in the elderly is influenced by interactions between the various elements of urban activity space. The elderly, who have more leisure time following retirement but often also have reduced physical function and illnesses, have become the most active people in terms of recreational physical activity. From the perspective of the activity space environment, in recent years identifying ways to promote leisure physical activity among the elderly has generated much research interest.
Regular physical activity has been reported to reduce risk of mortality [1,2] and coronary heart disease and to prevent chronic diseases such as diabetes, obesity, and some forms of cancer [3] or cognitive impairment [4]. Despite the importance of regular physical activity in preserving health, most elderly people are insufficiently active [5]. Aging statistics show that people over the age of 60 are the fastest growing segment of the China population [6], and that most older adults have a long-term or chronic disease. Therefore, efforts to promote increased levels of physical activity among older adults have become a new objective in public health [7]. Yet, current evidence is insufficient and mainly from non-China

Selection of participants
A multilevel cross-sectional study was conducted over 2 years (2015 and 2016) using a two-stage randomized sampling design in which the Communities and the older adults were the principal and the secondary units of parsing, respectively.
NanJing"s Communities, as defined by the Major's office, are not homogeneous in terms of built environment components and geographical parameters. Thus, this study used a modified notion of Community, defined as a residential area of similar Second, a random selection of older adults who met the following criteria were considered for selection: age ≥60 years and at least 2 years of local residency. The final sample included 586 individuals aged 60 years or older distributed across 30 communities (approximately 20 older adults per community).

Survey Questionnaire
To control for the influence of social variables such as education, income, and gender on the relationship between built environment and physical activity, subjects' educational qualifications (1= no schooling; 2 = Junior high school graduate; 3 = High school graduate; 4= College graduate); income (1= below 500 ¥; 7 2 = 500-1000 ¥; 3 = 1,001-2,000 ¥; 4 = 2,001-4,000 ¥; 5 = 4,000 ¥ or more) and gender (1= male; 2 = female) were included in the survey questionnaire and then entered into the analytical model as control variables. Occupations were divided according to the People's Republic of China Professional Classification, which defines four levels: the upper class (8), the middle class (66), working category (413), and lower class (1838). On the basis of the characteristics of our survey sample, occupational level was divided into the following types, effectively distinguishing between different social strata.

Determination of buffer distance
In this study, the accelerometer data was matched with the GPS data to calculate longitude. The linear distance between the latitude and longitude of the family residence and the physical activity place was estimated. The latitude and longitude of the home address is indicated as A1 B1 and the longitude and latitude of the activity record is indicated as A2 B2). Thus, Altogether, 586 subjects were surveyed. Data was collected from 2,483 physical activity sites of the family. The average was 1,018 m, with a median of 367 m. The average for male subjects was 985 m, with a median of 369 m. The average for female subjects was 1032 m with a median of 364 m. The average distance to a physical activity place for each family was much higher than the median distance.
The distance to the physical activity place for most urban elderlies was within the average of 1018 m. To explore the Basic Law of the distance from home to physical activity places for the urban elderly, 2,483 data were assessed according to 100 8 meter-intervals, and the number of groups was 20.

Definition of objective built environment
Using the GIS buffer technology to measure population density, the residential density, street connectivity, total road length, land-use mix, distance to public transport, distance to recreational facilities, and distance to commercial facilities within 1000 meters were determined.
This study focuses on the built environment characteristics for residents in the

Physical activity and sedentary time measurement
Actigraph GT3 Accelerometer was used to measure physical activity and sedentary time in the elderly. Data on physical activity was recorded for 4 consecutive days includes two working days and two rest days. Subjects wore the device for at least 8 h a day. On the fifth day, the investigators recovered and recorded the data for the 4 full days.
The data was downloaded and analyzed using Actilife (Version 6.  Table 1 shows the characteristics of all subjects in the samples as collected through the questionnaires. Subjects in this study had a higher average sex ratio at all levels of education and income than in the general population.

Daily Physical Activity Among the Elderly
A total of 586 older adults were required to wear Actigraph accelerometer,including 258 males and 328 females. As shown in Table 2 As can be seen in Table 3 model 1, the land-use mix distance to fitness venue is a factor affecting moderate-to-vigorous physical activity in the urban elderly (p 0.05).
The results showed that the land-use mix in which the elderlywere located could promote physical activity, and each additional unit of land-use mix could increase physical activity by 8.80 units.

Discussion
The present study examined the association of objective neighborhood built environment factors with moderate-to-vigorous physical activity and sedentary time in an older population in NanJing, China. The study used Buffer Technology to measure the population density, residential density, street connectivity, total road length, land-use mix, number of public transport stations, distance to public transport station, distance to recreational facilities, and distance to commercial facilities within 1,000 meters. The present study has some advantages. Some studies have recently reported associations between BEs and PA in China; however, they were mainly based on 13 subjective perceived measures. A few studies have analyzed a limited set of BE characteristics using GIS techniques. In contrast, we measured various BEs using GIS, which makes the results more objective. The present study also has some limitations. First, our study was cross-sectional in design, which prevents inferences being made about causality from the observed associations. A longitudinal study should be used to determine causal relationships. Second, the built environment is a large system that needs to include more indicators for analysis. Other variables including mental health, blood pressure, body mass index, and other health indicators should be included in a deeper study of this specific social group.

Conclusions
In summary, our findings provided support for the association between the built environment and physical activity among the Chinese elderly. Some characteristics of the built environment (e.g., land-use mix and distance to fitness venue) may affect MVPA, and a few more characteristics (e.g., population density and land-use mix) may also affect ST. In formulating urban planning policies, the above factors can be taken into consideration to promote physical activity among older people, helping them to modify their sedentary lifestyle and improve their overall health.

Ethics approval and consent to participate
This study does not involve invasive interventions on the human body. It is only a questionnaire survey, so it was approved orally by the Humanities Research Ethics Committee of Nanjing Normal University. All participants read a statement that explained the purpose of the survey and provided written informed consent before participation in the study. For those not willing to take part in the study, their right was respected to withdraw from the study. The study did not adversely affect the rights and welfare of the subjects and no financial compensation or provision was made.

Availability of data and materials
The datasets generated and/or analyzed during the current study are not publicly available due to maintain participant privacy and confidentiality requirements but are available from the corresponding author on reasonable request.

Consent for publication
Not applicable.

Competing interests
The authors declare that they have no competing interests.

Declaration
This manuscript has not been published or presented elsewhere in part or in entirety and is not under consideration by another journal. All study participants provided informed consent, and the study design was approved by the appropriate ethics review board. We have read and understood your journal's policies, and we believe that neither the manuscript nor the study violates any of these. There are no conflicts of interest to declare.   Schematic of the Gossip Garden 1000 m buffer zone