Body building for the nineties.

"Rest is precisely what aging people do not need," says William Evans of the U.S. Department of Agriculture's Human Nutrition Research Center on Aging at Tufts University.

And he's not just talking about people in their nineties.

Starting in middle age, people begin to gain fat and lose muscle, strength, bone, and aerobic capacity. Their risk of heart disease, diabetes, high blood pressure, and osteoporosis climbs. They're headed for what Evans calls The Disability Zone.

A healthy diet can help reduce those risks, but exercise is equally--and in some cases more--important. Evans isn't talking about aerobic exercise. The single most critical step to not just retard, but to reverse the aging process, he says, is strength-training.

Q: Why should older people exercise?

A: Much of what we call aging is nothing more than the accumulation of a lifetime of inactivity. Muscles shrink. Body fat increases. The results are an increased risk of diabetes, hypertension, and osteoporosis. By preserving muscle mass we can prevent these problems from occurring.

Q: How?

A: High-intensity weight-lifting. There's a myth that we lose the ability to respond to exercise as we age; that we can't get stronger or make muscles bigger. That's not true.

We can make people aged 65 stronger than they've ever been in their lives. We can make a 90-year-old stronger than a 50-year-old. Our oldest exerciser is 100 years old. We can triple muscle strength in old people.

Q: Which muscles?

A: In the older people, we're primarily interested in thigh muscles because we want to prevent falls.

But we also have a five-year project on muscle strength in postmenopausal women. Our goal is to strengthen legs, back muscles, and upper body--that's arm and chest--muscles.

When women lose weight by dieting, they lose not only muscle, but bone. If they weight-lift while losing weight, they can preserve bone.

Q: Are women at special risk?

A: Yes. There's a statistic from the Framingham Heart Study showing that half of women aged 65 can't lift ten pounds. Women have less muscle mass to begin with, and they start to lose muscle strength more rapidly after 60. They may become so profoundly weak that they have to be institutionalized.

But the health problems caused by inactivity don't suddenly show up on the doorstep at age 65. That's when they may manifest themselves as diabetes and hypertension. But they take decades to develop.

Q: What is high-intensity weight-lifting?

A: Lifting a weight heavy enough that you will be fatigued after eight or nine lifts. If you can lift a weight 15 times, it's too light. It won't increase strength.

We start people at about 60 to 80 percent of their maximum lifting capacity. In our nursing home patients, that's about five to ten pounds. In a healthy 65-year-old doing knee exercises, it's about 20 pounds.

Q: Why don't older people lift weights?

A: A lot stay away because they think it's bad for them. But if you do it properly, weight-lifting doesn't increase heart rate or blood pressure. It can be done without any potential danger.

Q: What is the proper way?

A: Don't hold your breath or lift too fast. Move slowly. Take time to warm up and cool down, because one thing that does change with age is that muscles get stiffer and connective tissue, such as the ligaments and tendons in the knees and ankles, gets weaker.

Whether exercise can prevent muscle stiffness is unclear. But you can get more limber and increase your range of motion.

And weight-lifting may promote weight-loss as well. The number of calories burned at rest is determined by muscle mass. So the more muscle mass you build, the more calories you burn.

Q: Must people take a class to learn strength training?

A: No. A huge number of people are intimidated about going into a class, so they must be able do it on their own.

And it can be done inexpensively. You can fill up a one-gallon milk container with water for an 8.3-pound weight. You can buy big rubber bands in a sporting goods store to tie to a chair to do resistance exercises.

Q: Isn't aerobic exercise more important?

A: Strength training and aerobic exercise do two different things. Aerobic exercise benefits the cardiovascular system. It increases HDL cholesterol. It may reduce the risk of dying of heart disease, diabetes, and even colon cancer.

Steve Blair of the Cooper Aerobics Institute in Dallas has shown that inactivity is as important a risk factor for premature death from all diseases and accidents as high cholesterol or any other risk factor.

If you have high blood pressure and you exercise, your risk of dying is less than if you don't have high blood pressure and don't exercise. If you smoke and exercise, your risk of dying is less than if you don't smoke and don't exercise. Exercise has a very powerful effect.

Q: How much aerobic exercise?

A: Three days a week, about 30 to 45 minutes a day. It's encouraging that you don't benefit much more from doing more.

We encourage walking more than any other aerobic exercise. You can do it with your spouse or friends.

We have our postmenopausal women on a walking program. They walk 45 minutes a day four times a week at 75 percent of their maximum heart rate. As they get more fit, we put weights around them so they don't have to run to maintain that heart rate.

Q: Is running dangerous?

A: If you take a person who's been sedentary all their life and start them running, the pounding and impact can cause injury. There's nothing wrong with running if you've done it all your life.

We've got a "Fitness After 50" program in Massachusetts. We have more than 7,000 walkers now. The average age is 66. But if I had to choose only one type of exercise for older people, it would be weight training.

Q: Why?

A: Because it has more to do with everyday functional activities. After age 65, body fat stays about the same, though that may be because people with higher fat levels die. Muscle weakness goes up rapidly after age 70.

We do CAT scans on legs. At age 20, 90 percent of the volume of the thigh is muscle. At age 90, it's only 30 percent muscle. The rest is fat and bone. That's one reason the biggest risk to older women is from falling down.

With weight-lifting, we can increase muscle mass ten percent, but the increase in strength is 200 percent.

Q: How much time does strength training take?

A: Two or three days a week to start. Only two days after you've gotten as strong as you want. That takes about three or four months. It takes an investment of time, but not that much.

Q: What is your primary goal?

A: We hope to keep people independent through exercise. The National Academy of Sciences said last year that if we could postpone institutionalization by just one month, it would save $3 billion in Medicare and Medicaid.

And that doesn't include the savings in dignity and independence for these people.