Frailty, Dr. Harris explains, involves exhaustion, weakness, weight loss and a loss of muscle mass and strength.

[First] in many cases, a single factor — undetected cardiovascular disease — is often a major reason people become frail.

partly blocked blood vessels in the brain, the legs, the kidneys or the heart. Those obstructions, in turn, can result in exhaustion or mental confusion or weakness or a slow walking pace.

Second finding is just as surprising to skeptical scientists because it seemed to many like a wrongheaded cliché — you’re only as old as you think you are.

Positive images may help push people along that path.

There is growing evidence that these subjective experiences might be more important than we thought.

[Third] being unable to walk a quarter mile within five minutes portended troubles. For each minute beyond five, the risk of dying in the next four years increased by a third, the risk of having a heart attack increased by 20 percent, and the risk of having a disability increased by half.

Could teaching people to walk farther and faster prevent their growing so weak they could hardly walk? Dr. Jack Guralnik, acting chief of the laboratory of epidemiology, demography and biometry at the National Institute on Aging, hopes it can.

Finding may be good news for today’s middle-age people who had the advantage of drugs to control their blood pressure and cholesterol levels before serious damage to blood vessels set in. And many are more active than their parents were when they were middle age.

Were there long-term effects of believing the stereotypes of aging?

People who had more positive views about aging were healthier over time.

Studies cannot tell for sure what is cause and what is effect.

Dr. Hodes confesses that in this case indirect studies may be the best that can be done.