TEN EXERCISE MYTHS.

1 Strength-training will make women too muscular.

"Many women are afraid that strength-training will make them bulky," says Miriam Nelson of the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tuffs University in Boston. "They think strength-training is only for men."

In fact, strength-training has enormous benefits for women. In one of Nelson's studies, postmenopausal women who were sedentary were randomly assigned to do strength-training exercises twice a week or to do no additional exercise. After a year, the strength-trainers had greater bone density, muscle mass, muscle strength, and balance than the sedentary women.(1)

"Women naturally have less bone and muscle than men, so they need to take care of what they've got," says Nelson. That's why women are at greater risk of osteoporosis than men. And lost muscle puts women at greater risk of disability as they age.

"Thirty percent of middle-aged women have trouble doing physical tasks like walking a mile or carrying a few grocery bags c. or climbing a few flights of stairs," says Nelson. "It's pretty staggering. They're really out of shape."

And don't worry about looking like a bodybuilder. "Women don't have enough testosterone to create big, bulky muscles," says Nelson. "To become a bodybuilder, women have to do a lot of weird things that most strength-training programs don't do."

2 Light weights on your arms or legs can boost your exercise benefit

Some people carry light (one- or two-pound) hand-held weights when they walk or run. Others strap velcro-fastened weights around their ankles. Don't bother, says exercise physiologist Ben Hurley of the University of Maryland.

"It slows you down, so you get less benefit from aerobic exercise, and it doesn't add enough weight to give you the benefits of strength-training," he explains.

To build muscle, you have to use weights that you can lift no more than eight to 12 times in a row. "If you can go beyond the twelfth repetition, the resistance is too light to stress the muscle," says Hurley. "As your muscles get stronger, you need to add more weight--or other resistance--so you can still do only eight to 12 repetitions."

3 With the right exercise, you can get rid of trouble spots.

"Some people believe that if they exercise one area, it will cause fat to be removed from that area," says Rosemary Lindle, a University of Maryland exercise physiologist.

"In our gym the men, who tend to store their fat in their abdomens, are on the ab machines, and the women are on the total hip machines for hours," she notes. "But spot-reducing is a myth."

Abdominal and hip exercises can strengthen and tone the muscles. But those muscles are underneath the "subcutaneous" layer of fat that gives the lovely appearance of flab. Only losing weight can get rid of excess fat, and where you lose the weight depends on your genes. Losing weight around the waist is easier than losing it at the hips.

"I tell women to do some strength-training in their upper body to create a better balance between upper and lower body," says Lindle. "You can build your own natural shoulder pads."

4 Exercise burns lots of calories.

"People have the mistaken idea that exercise is a fabulous way to lose weight," says William Evans of the University of Arkansas for Medical Sciences. "But exercising doesn't burn a lot of calories."

Walking or running a mile burns about 100 calories. But sitting still for the same time burns about 50 or 60 calories. "So the extra you expend isn't huge and people get discouraged at their slow rate of weight loss."

Another misconception: You keep burning considerably more calories for a long time after you stop exercising. "Calorie expenditure is elevated for the first minute or two, but by five or six minutes the extra expenditure is pretty small, and by 40 minutes post-exercise, it's back to where you started," says Evans.

That doesn't mean dieters should give up on exercise. The more you exercise, the more fit you'll get. That means you'll burn more calories because you can walk briskly or run for five miles instead of one. So instead of burning 100 calories, you burn 500 (that's 250 more than if you had stayed on the couch).

What's more, says Evans, "the better-conditioned you are, the more fat you burn for energy, because your muscles adapt to using an enzyme that oxidizes fat. People who are less-trained burn more carbohydrate instead."

Dieters who exercise also lose less lean body mass--that is, less muscle--than dieters who just cut calories. And physical activity can help with the toughest problem: keeping weight off.

Says Evans: "Studies show that after people lose weight, the best predictor of maintaining the weight loss is whether they exercise regularly."

5 If you don't lose weight, there's no point in exercising.

What gets most people off the couch and into their walking shoes? It's that unwanted flab that motivates most of us. It shouldn't.

"Many people don't see immediate weight loss and say it's all for naught and stop," says exercise expert William Haskell of Stanford University Medical School.

In fact, exercise has a laundry list of benefits beyond any impact on your next shopping trip (see "A Dozen Other Reasons to Exercise," p. 6). Among them:

"It improves the ability of insulin to enter cells, so it lowers the risk of diabetes," says Haskell. "It also lowers the risk of heart disease by improving blood clotting mechanisms, lowering triglycerides, and raising HDL ['good'] cholesterol."

Exercise alters not only your risk of disease, but your quality of life, he adds. "In our studies, exercise improved sleep in people with modest sleep dysfunction," that is, people who take a long time to fall sleep or who wake up frequently at night.

"The psychological benefits of exercise are frequently overlooked," says Haskell. "Exercise isn't a panacea, but it has consistently been shown to relieve both depression and anxiety."

6 Weight gain is inevitable as you age.

Most Americans get fatter as they get older ... but they don't have to. "It's a matter of reduced physical activity levels and lower metabolic rate caused by a loss of lean body mass [muscle]," says JoAnn Manson of Harvard Medical School.

"The lifelong loss of lean body mass reduces our basal metabolic rate as we age," says Arkansas's William Evans. "It's a very subtle change that begins between ages 20 and 30. The percentage of body fat gradually increases, and it produces an ever-decreasing calorie requirement."

That's because fat cells burn fewer calories than muscle cells. And a lower metabolic rate means that unless you eat less, you'll gain weight over the decades.

But exercise can mount a two-pronged attack on middle-age spread and muscle loss. Any activity makes you burn more calories (so you're less likely to wind up with an excess). And strength-training can offset the loss of muscle mass.

"Starting at age 40 in women and at 60 in men, we lose six to eight percent of our muscle per decade," says Maryland's Hurley. "However, after only two months of strength-training, women recover a decade of loss and men recover two decades."

That's with three weekly sessions that take 40 minutes each, including warm-up, rest periods, and stretching.(2) "The time spent doing the exercises that increase muscle mass is only about five minutes a session," says Hurley. Not a bad return on your time.

7 You can't be fit and fat.

"The notion that all fat people are sedentary and unfit and at high risk of disease is not true," says Steven Blair of the Cooper Clinic in Dallas, Texas. "Overweight and obese individuals who are fit do not have elevated mortality rates. We need to get off those people's backs."

But in Blair's study of 25,000 men who have come to the Cooper Clinic, ten percent of the normal-weight men--and half of the overweight men--were unfit.

Getting all of those unfit people--fat or thin--to move more could make a difference. In Blair's study, low fitness was as strong (or stronger) a predictor of dying as other risk factors, like high cholesterol, high blood pressure, and diabetes. Yet doctors rarely test a patient's fitness as part of a checkup.

"Fitness is such an important predictor of mortality, it's inexcusable not to evaluate it as part of a person's health risk," says Blair.

It wouldn't cost much. It's just a matter of measuring your heart rate--by measuring your pulse with a wristwatch--while you cycle, walk, or run at a given speed.

"A stress test for diagnosis of coronary heart disease at a major medical center can cost several hundred dollars," he says, "but you can go down to the YMCA and get a fitness test for 25 bucks."

8 No pain, no gain

"Many people still believe that you have to work at a very high intensity in order to get a benefit," says the Cooper Clinic's Steven Blair.

In fact, moderate-intensity exercise lowers the risk of dying just as much as high-intensity exercise. For example, says JoAnn Manson of the Harvard Medical School, "in the Nurses' Health Study, women who regularly engaged in brisk walking reduced their risk of heart disease to the same degree as women who engaged in vigorous exercise. You don't need to run a marathon."

The trick is making sure that the exercise is at least moderate-intensity--that is, equivalent to walking at a pace of three to four miles an hour.

"You can vacuum at a very low pace or at a moderately intense pace," says Blair. Running or jogging is, by definition, high-intensity. But walking, raking leaves, mowing lawns, dusting, and gardening may be either moderate- or low-intensity.

High-intensity exercise does have one advantage: it saves time. It takes less time to burn the same number of calories at higher intensity.

"You can jog for 20 minutes or walk for 40 or 45," says Blair. "You pay your money and you take your choice."

Does all the heart-pounding of high-intensity exercise do anything else for you? "Some things probably respond better to high-intensity and some may respond better to moderate-intensity exercise," says Blair. "But in general, there doesn't appear to be a lot of difference as long as you expend the same number of calories."

9 If you can't exercise regularly, why bother?

It takes ten to 12 weeks of regular exercise to become "fit"--that is, to improve your performance on a treadmill (a measure of your oxygen capacity). But your health can improve after that first brisk walk or run.

"Take a 50-year-old man who is somewhat overweight and typically has moderately elevated blood sugar, triglycerides, or blood pressure," says Stanford's William Haskell. "A single bout of exercise of moderate intensity--like 30 to 40 minutes of brisk walking--will lower those numbers."

And not just while you're moving. "If you exercise at, say, five o'clock in the afternoon, the improvement will be there the next morning," he adds.

That may be why postal carriers (or others who are active at work) have a lower risk of heart disease than postal clerks (or others who are sedentary at work). "There's not much difference in their fitness levels, but the carriers have lower blood sugar, triglycerides, and blood pressure," says Haskell.

People should still try to at least follow the Center for Disease Control's modest advice to get at least 30 minutes of moderate activity on most--or preferably all--days of the week, he adds. But if you can't, don't let that stop you from taking even a single walk.

"Every bout has benefits," says Haskell.

10 If you didn't exercise when you were younger, it could be dangerous to start when you're older.

"Many people think they're too old to start an exercise program," says Tuffs University's Miriam Nelson. "They think it's unsafe because they have heart disease or diabetes or because they're too out of shape to start."

You're never too old to start, says Nelson. And she ought to know. In one Tufts study, the participants were frail nursing-home residents whose ages ranged from 72 to 98. After just ten weeks, strength-training improved their muscle strength, ability to climb stairs, and walking speed.(3) "When they see what a difference it makes, they're thrilled," says Nelson.

The same goes for people with chronic diseases. "People say they can't exercise because they have arthritis," she adds. "But we see some of the greatest benefits in people with arthritis. Exercise reduces pain and increases range of motion, strength, and mobility."

That doesn't mean that anyone can plunge into a bout of vigorous exercise, regardless of health history. In a recent study, ordinarily inactive people--especially men who had high cholesterol or angina or were smokers or obese--were ten times more likely to have a heart attack within an hour of exerting themselves (usually by jogging or heavy lifting) than at other times.(4) Anyone with multiple risk factors for heart disease should check with a physician and start slowly.

As for the all-too-common "I don't have time to exercise," Nelson responds, "somehow, you've got to make the time, or you're going to have medical problems like heart disease, diabetes, or osteoporosis. And it will take a lot more time to deal with them than it takes to exercise."

(1) Amer. Med. Assoc. 272:1909, 1994.

(2) J. Appl. Physiol. 86:195, 1999.

(3) N. Eng. J. Med 330:1769, 1994.

(4) J. Amer. Med. Assoc. 282:1731, 1999.