Physical Distancing Measures and Walking Activity in Middle-aged and Older Residents in Changsha, China, During the COVID-19 Epidemic Period: Longitudinal Observational Study oleh Wang, Yilun, Zhang, Yuqing, Bennell, Kim, White, Daniel Kenta, Wei, Jie, Wu, Ziying, He, Hongyi, Liu, Shaohui, Luo, Xianghang, Hu, Shuo, Zeng, Chao, Lei, Guanghua