Physical Inactivity Syndrome: A Risk Factor and Target for Intervention-A Narrative Review

The aging of the world's population has caused a dramatic change in the overall health of patients, with many suffering from disuse syndrome-a condition caused by immobility and bed rest. Even among people who are able to live independently, newly defined issues such as frailty, sarcopenia, locomotive syndrome, and hospitalization-associated disability have rapidly emerged, and it has been found that physical inactivity is a key cause of these issues. Disuse syndrome is a term that is mainly used in Japan but not widely accepted elsewhere because of its negative connotations. Moreover, although the term physical inactivity is widely used, it has a strong connotation of simply referring to reduced physical activity and does not emphasize that it also poses systemic and multi-organ risks. To solve these problems, in this narrative review, I propose a new academic term-physical inactivity syndrome (PIS)- to describe the diverse physical, mental, and social symptoms and disorders caused by bed rest and decreased physical activity. PIS serves as an umbrella term for disuse syndrome, physical inactivity, frailty, sarcopenia, and related diseases. Furthermore, the effects of rehabilitation and exercise therapy required to prevent and treat PIS are introduced. It is necessary for medical professionals to be fully aware of the risks of PIS, properly acquire the skills needed to improve patient activity, and carry out prevention and treatment with sufficient confidence.