Misconceptions about Exercise Can Sabotage Your Efforts to Get in Shape

Here are the facts behind 10 common myths.

In a recent Op-Ed piece in The New York Times, Martina Navratilova decried one of sport's most persistent myths - that women lack stamina and endurance. That's why their tennis matches are limited to three sets, while men's matches can go five sets. Actually, the physiological differences that make men more muscular than women confer no edge in endurance. Women can exercise at least as hard and long as men can. And they recover from a grueling workout significantly faster than men do.

While scientists and female athletes are finally laying that myth to rest, other antiquated notions about exercise have stubbornly persisted - and new misconceptions keep popping up. Such incorrect notions can discourage you from exercising or lead you to waste time, effort, or money on workouts that don't really work. They can even harm your health. Here are the facts about 10 unfounded fears, negative notions, and false hopes about working out.

Fact: Strenuous workouts do improve aerobic capacity far more than light or moderate workouts do. While that may improve athletic performance, it does not necessarily translate into a great health advantage.

The death rates from coronary heart disease, cancer, and all causes combined are much lower in moderate exercisers than in non exercisers; but they're only a little lower in heavy exercisers than in moderate exercisers. The same holds true for the risk of developing type II diabetes, by far the most common kind.

In addition, non strenuous exercise seems to reduce stress, anxiety, and blood pressure as effectively as strenuous exercise does. And moderate exercise like walking can do just as much to control weight as vigorous exercise like jogging, since the number of calories burned depends on how much ground you cover, not how fast you cover it. In fact, moderate exercise is potentially more effective than vigorous for most people, since they can walk much further than they can run.

Fact: There's no such thing as "spot reduction." When you exercise, you use energy produced by burning fat in all parts of your body - not just around the muscles that are doing most of the work. In fact, your genes may dictate that fat disappears from, say, your face or arms before your belly, even if you do endless abdominal exercises. However, working a specific region like the belly can have one site-specific benefit: Strengthening the muscles can make you look thinner by helping you hold in your gut.

Myth #3: The more you sweat during exercise, the more fat you lose.

Fact: The harder you work out, the more calories you'll burn within a given period and thus the more fat you stand to lose. But how much you sweat does not necessarily reflect how hard you're working. Some people tend to sweat profusely due to heavy body weight, poor conditioning, or heredity. And everyone sweats more in hot, dry weather or dense clothing than in cool, humid weather or porous clothing. (You may feel as if you're sweating more in humid weather; but that's because moist air slows the evaporation of sweat.)

Exercising in extremely hot weather or in a plastic "weight loss" suit will indeed make you sweat heavily and lose weight immediately. But that lost weight is almost entirely water; the pounds will return when you replenish your fluids by drinking after the workout. Further, you could develop heat exhaustion if you push yourself too hard in extreme heat or in plastic clothes. which prevent sweat from evaporating and, in turn, cooling you off.

Fact: Sports drinks contain two main ingredients that are theoretically beneficial for exercisers: sodium, which helps the body retain water, and sugar, which the body burns for energy. But very few people exercise hard enough to sweat away much sodium or to use up their carbohydrate reserves, which the body converts to sugar. You'd have to jog for at least two hours, for example, before your carbohydrate stores would start to run low. So unless you're doing a marathon or other exhaustive exercise, plain water is all you need.

Fact: Aerobic exercise, such as jogging or brisk walking, may indeed increase your appetite - but only, it seems, if you need extra calories. Studies suggest that lean individuals do get hungrier after such exercise; that helps prevent them from getting too thin. In contrast, working out does not seem to boost appetite in obese individuals; so exercise should help them slim down.

Fact: Strength training, using either weights, machines, or elastic bands, can substantially increase the number of calories you burn. A typical session, in which you rest briefly after each muscle-building maneuver, uses up calories at least as fast as walking does. Circuit training, in which you move quickly from one strengthening maneuver to the next, burns calories faster than walking does. And your body continues to burn calories for hours after either type of strength training. More important, the muscle you build consumes calories more rapidly, even when you're not exercising.

In one study, three months of strength training boosted the average calorie-burning rate by an average of 7 percent, burned off 4 pounds of fat, and added nearly that much muscle. Since muscle is denser than fat, the volunteers presumably did become thinner. Equally important, they burned off that fat despite a 15 percent increase in their calorie content. If the researchers hadn't prodded them to maintain their weight by eating more than they felt like eating, the volunteers almost surely would have lost weight.

Strength training is particularly helpful as part of a comprehensive weight-loss program that includes both aerobic exercise - which burns lots of calories during the workout and some calories after the workout - and a moderately low-calorie diet. (forget crash diets, which almost always never work and can be dangerous.) A recent study found that women who ate a moderately restrictive diet and did either strength training or aerobic exercise lost more weight than those who only dieted. But those who split their workout time between strength training and aerobic exercise lost the most weight of all.

Fact: Strength training plus aerobic exercise may be the ideal exercise regimen not only for the waistline but also for the heart. One analysis of 11 clinical trials found that strength training can reduce levels of LDL cholesterol, the artery-clogging kind (though it has little effect on HDL cholesterol, the artery-clearing kind). Aerobic exercise has a complimentary benefit: It improves HDL but does little for LDL. Further, some studies suggest that strength training, like aerobic exercise, may help reduce blood pressure. (But check with your doctor for guidance before starting a muscle-building program if you have hypertension, since straining can temporarily increase blood pressure.) One final benefit: By fortifying the muscles, strength training reduces the likelihood that sudden or unaccustomed exertion, such as moving furniture or shoveling snow, will trigger a heart attack.

Fact: Lack of exercise does make the muscles shrink, reducing the body's calorie-burning rate. The lack of activity itself further reduces the number of calories you burn. So people who stop working out are indeed in danger of getting flabby.

But that doesn't mean that muscle actually turns to fat - they're totally different types of tissue. Nor does it mean you're doomed to gain fat around the muscles after you stop exercising; you just need to cut back on the calories you consume. (Of course, the best way to stay slim is to eat a lean diet and continue to exercise regularly.)

Fact: If you strength train without moving your joints through their full range of motion, you can indeed lose flexibility. But strength training can actually improve flexibility if you do move your joints fully. Stretch after a muscle-building workout to help keep yourself limber.

Fact: It's very difficult for most women to build large muscles. That's because women have relatively low levels of the hormone testosterone, which influences muscle growth. Both men and women can build firmer rather than bulkier muscles by working against lighter resistance more than 25 times rather than heavier resistance fewer times.