As a medical resident 30 years ago, Ava Kaufman remembers puzzling over some of the elderly patients who came to the primary-care practice at George Washington University Hospital. They weren't really ill, at least not with any identifiable diseases. But they weren't well, either.

They were thin and weak. They had no energy. They tired easily. Their walking speed was agonizingly slow. "We couldn't put our finger on a specific diagnosis or problem," Kaufman said. "We didn't have a word for it then."

Today we do. It is called frailty. There have always been frail people, but only in recent years has the term "frailty" become a medical diagnosis, defined by specific symptoms and increasingly focused on by those who deal with the elderly. Clinicians now are looking at ways to prevent or delay frailty — and sometimes even reverse it.