Older people can easily lose their ability to walk, get in and out of a chair, or tackle stairs for a range of medical reasons, such as stroke, frailty with advancing age, weakness and instability after a hip fracture, or just being 'laid low' after an infection or worseing of existing cardiac/respiratory disease. Any of these sorts of problems can mean people don't get up and about for a prolonged period so they lose their balance skills and exercise capacity.
People with mobility problems due to age or neurological conditions benefit from inpatient rehabilitation, especially if high doses of exercise are used. However, many people admitted to a rehabilitation hospital are inactive for large portions of their day due to limited numbers of physiotherapists and other members of the rehabilitation team.
Interactive computer or video games that are driven by the player's whole body movements (like Wii or X-box Kinect) are known as ‘Exer-games’ and may increase the dosage of exercise within and outside of therapy sessions.