**1.1 Worldwide spread of COVID-19 and refraining from leaving the home among the aged**

The spread of the coronavirus infection caused by the novel severe acute respiratory syndrome coronavirus 2 has had a major impact on people's lives [1, 2]. Within approximately 1 month after the global outbreak of coronavirus disease 2019 (COVID-19), when it was declared a pandemic by the World Health Organization, the average number of steps taken by 455,404 people in 187 countries was reported to have decreased by 27.3% [3]. In Japan, a state of emergency was declared, and many people were forced to refrain from going out and to restrict their social activities. They were also encouraged to stay indoors to avoid the "Three Cs" (closed spaces, crowded places, and close-contact settings). Because higher mortality rates were reported among older patients and those with underlying medical conditions [4], older individuals more strictly refrained from activities. In fact, in a survey of 1600 older persons aged 65 years and older, physical activity levels were approximately 30% lower than before the spread of COVID-19 [5, 6]. Although a trend toward less restraint with respect to engagement in activities has recently been seen, many older people remain at increased risk of frailty or deteriorating to a level requiring nursing care as the COVID-19 pandemic continues unabated. The risk of frailty or deterioration to the state of requiring long-term care is therefore increasing.
