The assumption at the heart of the fitness revolution has always been that activity and proper diet are good for us when we're young and will help stave off disease and disabilities as we age.
Now, proof that exercise is beneficial for older people is emerging from a federally funded research project -- known as "Fitness over 50" -- that measures the physiological status of active seniors.
"We clearly have people in the program over 70 with no evidence of heart disease," says Dr. Andrew Goldberg, professor of medicine at the University of Maryland and primary researcher in the project. "They have cardiac and metabolic profiles such that if I lined them up with 25-year-olds, I couldn't tell the difference."
With volunteers who enter the program at various levels of fitness -- from top-level "masters athletes" down to couch potatoes -- the exercise emphasis has been on aerobic activities such as walking, biking and jogging.
So far, only men have been studied, though the program will begin evaluating women in the next few months. Even on the men, all the data aren't in yet. But after about five years of study, many improvements have been documented.
As the men become more active, their ability to use oxygen -- known as "VO-2 max" -- increases. "This is probably the best test of overall well-being," Dr. Goldberg says. "You can't get a good result unless the muscles, heart and pulmonary system are in good shape, and glucose and fat are being utilized efficiently.
"Our people go further on the treadmill; their exercise capacity is greater. One study shows an increase in cardiac blood flow. High density lipoproteins go up. Triglycerides go down. Glucose metabolism increases: If you put a diabetic on a treadmill for half an hour, you can get the same decrease in glucose as with a shot of insulin."
Furthermore, psychological and neurological tests have shown that older men who exercise and lose weight are happier and more competent in daily activities than sedentary men who lose weight by dieting alone.
Active older men also eat as much as younger men, disproving the widely held assumption that appetite normally decreases in the elderly. And, he adds, while many older people lose some of their ability to discern sweet and sour tastes, a recent study found that active men retained it.
At the University of Maryland College Park, meanwhile, a companion study is trying to clarify the benefits of weightlifting in older men.
Last April, Ben Hurley, Ph.D., director of the exercise physiology lab at College Park, recruited 14 men aged 50 to 69 who had not weight-trained for at least a year. Using weight machines, he trained them to move increasingly heavy loads:
"So far, the average person has increased more than 100 pounds NTC on the legs; the average increase in upper body power is 30 to 50 percent," Dr. Hurley says. "And from questioning them, we find there's no soreness."
Muscle mass has also increased in the seven subjects analyzed so far, while the fat around the muscle and under the skin has decreased.
In previous studies, Dr. Hurley found that strength-training leads to more efficient use of blood sugar, which reduces the risk of diabetes; since diabetes is a risk factor for heart disease, better glucose metabolism reduces the risk of heart disease as well.
The current study expands and helps explain the former: Bigger muscles not only make you stronger and better looking; they may also make you healthier.
While most formal studies of exercise and the elderly have concentrated on men, it is widely assumed that active women reap similar benefits in terms of heart health, diabetes prevention and control, and avoidance of weight gain.
Additionally, women who engage in weight-bearing activity through life are less likely to have osteoporosis in old age, and older women who become more active may be able to retard or even reverse the bone loss.
In neither men nor women, however, is activity a means for regaining lost youth.
VO-2 max improves in older exercisers, but younger people still have a better oxygen delivery system bodywide, according to Dr. Goldberg. Moreover, older people are more susceptible to dehydration during exercise and are more likely to have problems with balance or in adapting to differences in terrain.
"If a younger person is running and has to jump over a hole, he might stumble and then correct himself; an older person will fall," Dr. Goldberg says.
But if turning back the clock is impossible, activity does seem tkeep it from running faster.
"I maintain what I have, but I could no longer make the Ohio State track team," says Heinz Lenz, 65, one of the Fitness over 50 masters athletes.
An assistant professor of physical education at the U.S. Naval Academy whose responsibilities include whipping the first-summer plebes into shape, Mr. Lenz defines physical fitness in practical terms: