Myth 1. While light exercise does yield some benefits, it's not nearly as beneficial as strenuous exercise.
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.

Myth 2. You can lose fat from specific parts of your body by exercising those spots.
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 abdomen.

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.

Myth 4. Sports drinks help you exercise more safely and effectively.
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.

Myth 5. Aerobic exercise tends to make you hungry, so it actually undermines your efforts to lose weight.
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.