1. Ren, L.L.; Wang, Y.M.; Wu, Z.Q.; Xiang, Z.C.; Guo, L.; Xu, T.; Jiang, Y.Z.; Xiong, Y.; Li, Y.J.; Li, X.W.; et al. Identification of a novel coronavirus causing severe pneumonia in human: A descriptive study. Chin. Med. J. 2020, 133, 1015–1024. [CrossRef] [PubMed]
2. Prime Minister of Japan and His Cabinet. Declaration of a State of Emergency in Response to the Novel Coronavirus Disease. 16 April. Available online: http://japan.kantei.go.jp/ongoingtopics/_00020.html. (accessed on 24 August 2020).
3. Maugeri, G.; Castrogiovanni, P.; Battaglia, G.; Pippi, R.; D’Agata, V.; Palma, A. The impact of physical activity on psychological health during Covid-19 pandemic in Italy. Heliyon 2020, 6, e04315. [CrossRef] [PubMed]
4. Stanton, R.; To, Q.G.; Khalesi, S.; Williams, S.L.; Alley, S.J.; Thwaite, T.L.; Fenning, A.S.; Vandelanotte, C. Depression, anxiety and stress during COVID-19: Associations with changes in physical activity, sleep, tobacco and alcohol use in australian adults. Int. J. Environ. Res. Public Health 2020, 17, 4065. [CrossRef] [PubMed]
5. Lesser, I.A.; Nienhuis, C.P. The impact of COVID-19 on physical activity behavior and well-being of canadians. Int. J. Environ. Res. Public Health 2020, 17, 3899. [CrossRef] [PubMed]
6. Physical Activity Guidelines Advisory Committee. Introducing the physical activity guidelines for Americans. In Physical Activity Guidelines for Americans, 2nd ed.; Department of Human and Health Services: Washington, WA, USA, 2018; p. 21. [CrossRef]
7. Lautenschlager, N.T.; Almeida, O.P.; Flicker, L.; Janca, A. Can physical activity improve the mental health of older adults? Ann. Gen. Hosp. Psychiatry 2004, 3, 12. [CrossRef]
8. Sun, F.; Norman, I.J.; While, A.E. Physical activity in older people: A systematic review. BMC Public Health 2013, 13, 449. [CrossRef]
9. Scully, D.; Kremer, J.; Meade, M.M.; Graham, R.; Dudgeon, K. Physical exercise and psychological well being: A critical review. Br. J. Sports Med. 1998, 32, 111–120. [CrossRef]
10. Cooney, G.M.; Dwan, K.; Greig, C.A.; Lawlor, D.A.; Rimer, J.; Waugh, F.R.; McMurdo, M.; Mead, G.E. Exercise for depression. Cochrane Database Syst. Rev. 2013, 311, 2432–2433. [CrossRef]
11. Nguyen, H.C.; Nguyen, M.H.; Do, B.N.; Tran, C.Q.; Nguyen, T.T.P.; Pham, K.M.; Pham, L.V.; Tran, K.V.; Duong, T.T.; Tran, T.V.; et al. People with suspected COVID-19 symptoms were more likely depressed and had lower health-related quality of life: The potential benefit of health literacy. J. Clin. Med. 2020, 9, 965. [CrossRef]
12. Teixeira, P.J.; Carraça, E.V.; Markland, D.; Silva, M.N.; Ryan, R.M. Exercise, physical activity, and self-determination theory: A systematic review. Int. J. Behav. Nutr. Phys. Act. 2012, 9, 78. [CrossRef]
13. Bauman, A.E.; Reis, R.S.; Sallis, J.F.; Wells, J.C.; Loos, R.J.F.; Martin, B.W. Correlates of physical activity: Why are some people physically active and others not? Lancet 2012, 380, 258–271. [CrossRef]
14. Inoue, S.; Murase, N.; Shimomitsu, T.; Ohya, Y.; Odagiri, Y.; Takamiya, T.; Ishii, K.; Katsumura, T.; Sallis, J.F. Association of physical activity and neighborhood environment among Japanese adults. Prev. Med. 2009, 48, 321–325. [CrossRef] [PubMed]
15. Koyano, W.; Shibata, H.; Nakazato, K.; Haga, H.; Suyama, Y. Measurement of competence: Reliability and validity of the TMIG index of Competence. Arch. Gerontol. Geriatr. 1991, 13, 103–116. [CrossRef]
16. Fujiwara, T.; Kondo, K.; Shirai, K.; Suzuki, K.; Kawachi, I. Associations of childhood socioeconomic status and adulthood height with functional limitations among Japanese older people: Results from the JAGES 2010 project. J. Gerontol. 2014, 69, 852–859. [CrossRef] [PubMed]
17. Yasunaga, A.; Park, H.; Watanabe, E.; Togo, F.; Park, S.; Shephard, R.J.; Aoyagi, Y. Development and evaluation of the physical activity questionnaire for elderly Japanese: The Nakanojo study. J. Aging Phys. Act. 2007, 15, 398–411. [CrossRef]
18. Awata, S.; Bech, P.; Yoshida, S.; Hirai, M.; Suzuki, S.; Yamashita, M.; Ohara, A.; Hinokio, Y.; Matsuoka, H.; Oka, Y. Reliability and validity of the Japanese version of the world health organization-five well-being index in the context of detecting depression in diabetic patients. Psychiatry Clin. Neurosci. 2007, 61, 112–119. [CrossRef]
19. Ware, J.E.; Kosinski, M.; Keller, S.D. A 12-item short-form health survey: Construction of scales and preliminary tests of reliability and validity. Med. Care 1996, 34, 220–233. [CrossRef]
20. Stults-Kolehmainen, M.A.; Sinha, R. The effects of stress on physical activity and exercise. Sports Med. 2014, 44, 81–121. [CrossRef]
21. Lau, J.T.F.; Griffiths, S.; Choi, K.C.; Tsui, H.Y. Avoidance behaviors and negative psychological responses in the general population in the initial stage of the H1N1 pandemic in Hong Kong. BMC Infect. Dis. 2010, 10, 139. [CrossRef]
22. Cleland, V.J.; Ball, K.; Salmon, J.; Timperio, A.F.; Crawford, D.A. Personal, social and environmental correlates of resilience to physical inactivity among women from socio-economically disadvantaged backgrounds. Health Educ. Res. 2010, 25, 268–281. [CrossRef]
23. Questionnaire of WHO-5-J. Available online: https://www.psykiatri-regionh.dk/who-5/Documents/WHO5_ Japanese.pdf (accessed on 15 July 2020).
24. Olsen, L.R.; Jensen, D.V.; Noerholm, V.; Martiny, K.; Bech, P. The internal and external validity of the major depression inventory in measuring severity of depressive states. Psychol. Med. 2003, 33, 351–356. [CrossRef] [PubMed]
25. Bowler, D.E.; Buyung-Ali, L.M.; Knight, T.M.; Pullin, A.S. A systematic review of evidence for the added benefits to health of exposure to natural environments. BMC Public Health 2010, 10, 456. [CrossRef] [PubMed]
26. Nguyen, J.; Brymer, E. Nature-based guided imagery as an intervention for state anxiety. Front Psychol. 2018, 9, 1858. [CrossRef]
27. Dwyer, M.J.; Pasini, M.; De Dominicis, S.; Righi, E. Physical activity: Benefits and challenges during the COVID-19 pandemic. Scand J. Med. Sci. Sports 2020, 30, 1291–1294. [CrossRef] [PubMed]
28. Hammami, A.; Harrabi, B.; Mohr, M.; Krustrup, P. Physical activity and coronavirus disease 2019 (COVID-19): Specific recommendations for home-based physical training. Manag. Sport Leis. 2020. [CrossRef]
29. Aubertin-Leheudre, M.; Rolland, Y. The importance of physical activity to care for frail older adults during the COVID-19 pandemic. J. Am. Med. Dir. Assoc. 2020, 21, 973–976. [CrossRef]
30. Loh, R.; Stamatakis, E.; Folkerts, D.; Allgrove, J.E.; Moir, H.J. Effects of interrupting prolonged sitting with physical activity breaks on blood glucose, insulin and triacylglycerol measures: A systematic review and meta-analysis. Sports Med. 2020, 50, 295–330. [CrossRef]
31. Kim, G.M.; Hong, M.S.; Noh, W. Factors affecting the health-related quality of life in community-dwelling elderly people. Public Health Nurs. 2018, 35, 482–489. [CrossRef]
32. Jalenques, I.; Rondepierre, F.; Rachez, C.; Lauron, S.; Guiguet-Auclair, C. Health-related quality of life among community-dwelling people aged 80 years and over: A cross-sectional study in France. Health Qual. Life Outcomes 2020, 18, 126. [CrossRef]
33. Lee, T.W.; Ko, I.S.; Lee, K.J. Health promotion behaviors and quality of life among community-dwelling elderly in Korea: A cross-sectional survey. Int. J. Nurs. Stud. 2006, 43, 293–300. [CrossRef]
34. Sørensen, K.; Van Den Broucke, S.; Fullam, J.; Doyle, G.; Pelikan, J.; Slonska, Z.; Brand, H. Health literacy and public health: A systematic review and integration of definitions and models. BMC Public Health 2012, 12, 80. [CrossRef] [PubMed]
35. Ishikawa, H.; Yano, E. Patient health literacy and participation in the health-care process. Heal. Expect. 2008, 11, 113–122. [CrossRef] [PubMed]
36. Jayasinghe, U.W.; Harris, M.F.; Parker, S.M.; Litt, J.; van Driel, M.; Mazza, D.; Del Mar, C.; Lloyd, J.; Smith, J.; Zwar, N.; et al. The impact of health literacy and life style risk factors on health-related quality of life of Australian patients. Health Qual. Life Outcomes 2016, 14, 68. [CrossRef] [PubMed]