Regular physical activity (PA) confers a range of health benefits for adults, including reduced risk of developing heart disease, stroke, type 2 diabetes, and some cancers [
1]. Despite public health efforts to promote PA, low levels of PA among adults are reported in many countries [
2]. In Japan, only 36% of men and 29% of women had a physical activity habit (engaging in at least 30 min of physical activity twice a week for the last 12 months) in 2017, and the prevalence has been stable for the last 10 years [
3]. Increasing population-level PA is thus a public health priority. Many PA promotion programs that have been implemented tend to focus on individual motivation to exercise, but such approaches are known to be less successful in sustaining long-term behavioral changes [
4]. It is now recognized that strategies focusing only on individuals are unlikely to be sufficient to increase PA at the population level [
5]. To promote PA more effectively, the ecological model of health behavior is increasingly being adopted to guide PA interventions [
6]. The ecological model posits that factors at multiple levels (individual, social/community, environmental, and policy) influence individual behaviors and that interventions addressing multi-level influences are more effective [
7]. A Cochrane review on community-wide interventions to increase PA also supports the importance of environmental components [
8]. An important principle of the ecological model is to make participation in PA easy and accessible through various means, such as providing social support, removing barriers, and creating more opportunities to be active.
Exercise and recreational facilities where near-by residents can engage in a range of physical activities can be an important community resource to promote PA. A review of recreational environments and PA found that outdoor recreational facilities such as parks and trails are associated with residents’ PA, but most studies were cross-sectional in design [
9]. For instance, better access to sports facilities was found associated with a greater amount of physical activity in Korean adults [
10]. A Danish study using GPS and accelerometer also found that having sports facilities nearby (within 800 m from home) was associated with a longer duration of moderate-to-vigorous PA [
11]. There are some natural experimental studies examining the impact of improving PA facilities. An Australian study examining the impact of playground refurbishment found increased visitors and active users after restoration [
12]. Similarly, a study on park renovation in the U.S. found increased visitation and more energy expenditure by park visitors after park improvement [
13]. An observational cohort study in Finland has shown that participants moving to areas where access to sports facilities was poorer (increased distance to and decreased number of them) decreased their PA levels in comparison to before the move [
14]. However, a recent systematic review of natural experiments has reported that research has not yet examined the impact of a new exercise facility on residents’ PA [
15]. Considering that building a sports facility is a major investment to promote community health, it is important to understand whether it is effective in increasing the level of PA in the community. This study examined the impact of a newly constructed multipurpose exercise facility on community-level PA, perceived availability of PA facilities, awareness of others being active, and willingness to engage in PA in Japan. A focus of this study was on mid-to-older aged adults, who can particularly benefit from additional PA, given that their daily activity levels are lower compared to younger adults [
16].