SAN JOSE - No pain, no gain.

Go for the burn.

The only exercise that helps you lose weight is pushing yourself away from the table.

With fitness advice like this, is it any wonder so many of us find it hard to stick to an exercise routine?

That's why we've gathered 10 cherished Fitness Beliefs - and have tried to smash them to bits. Or at least figure out the current thinking on them.

But before we get started . . .

Pain: Not good. A sign you're doing something wrong.

Burn: Not good. A sign you may be injured soon.

Exercise's effect on weight loss: Good, especially aerobic exercise. Also, several studies have shown that appetite decreases, not increases, with exercise.

And now, let's just do it.

Fitness Belief No. 1

If you're not going to exercise vigorously, you might as well not exercise at all.

It all depends on what you want to accomplish with exercise. Good health? Long life? Beating your brother-in-law in driveway basketball?

Briefly, if you're in training for competition, you need to keep your exercise sessions vigorous. But if you're exercising to improve health and increase your quality of life, you can be more moderate in your habits.

How moderate is a matter of opinion.

For years, the rule of thumb has been that exercising 20 minutes or longer three times a week at 60 to 85 percent of your maximum heart rate will improve fitness and lower the risk of heart disease and other cardiovascular problems.

Then, in February, the American College of Sports Medicine and Centers for Disease Control issued the recommendation that "adults accumulate 30 minutes or more of moderate-intensity physical activity on most, preferably all, days." That meant more total time spent exercising, but the exercise could be accomplished in small chunks - even 10 minutes at a time - and mundane activities such as climbing stairs and walking briskly counted, as long as you did them briskly enough. This will help ensure good health.

Soon after, Harvard researchers released a study of 17,321 men that showed only vigorous exercise - exercise that requires at least six times as much energy as resting - prolongs life.

And just this fall, a study of 1,800 women runners conducted at the Lawrence Berkeley Laboratory concluded that women who run up to 40 miles a week increase their levels of HDL or "good" cholesterol and show more improvement in blood pressure, pulse rates and weight loss than those who run only 10 miles a week.

Hoo boy.

At least one thing remains clear: It doesn't matter how hard or long you plan to exercise if you never actually do it. Find an exercise you enjoy (or at least one you can tolerate) at an intensity level you can handle and keep at it.

Fitness Belief No. 2

Flabby thighs? You can spot reduce.

You can indeed tone muscles and increase strength by performing targeted exercises, and this can lead to changes in appearance. But burn fat in one specific part of the body?

"No," says Art Weltman, director of the exercise physiology program at the University of Virginia. "And the reason is that fat is mobilized during exercise by hormones, and because hormones circulate in the blood, they mobilize fat from all regions."

That is, when your body loses fat, it loses fat from all over.

There are some areas where the fat is more active than others, and hence somewhat easier to lose, Weltman says. Abdominal fat is generally a little easier to lose than fat on the hips and buttocks. But targeting the exact spot from which you'd like to drop five pounds? Forget it.

Fitness Belief No. 3

Never exercise every day - your body needs a rest.

Not necessarily.

Exercise physiologists recommend taking a day off every now and then to let your muscles recover, especially from hard workouts. But, says Weltman, "You can exercise every day as long as you change the intensity of the exercise."

Muscles need about 48 hours to recover from strenuous workouts, says Weltman, which explains why people vary their workouts: hard one day, easy the next, hard the third day and so on.

Or, you can change the muscle groups you're using: jog one day, swim the next, ride a bike on the third, lift weights on the fourth.

"Use your body as a guide," says Weltman. "If you have a hard day, and you feel lousy the next day, take another easy day or a day off."

Fitness Belief No. 4

If you're not lifting weights to the point at which you can lift no more, you're not really training.

"I think that if you're trying to compete for Mr. America or Ms. America bodybuilding competitions, the idea of maximal exertion makes sense," says William Haskell, deputy director of the Stanford Center for Research in Disease Prevention.

"But there has been a series of studies that show for increase of muscle mass in the general public, resistance exercise or weight training can really be much more moderate."

For healthy adults, the American College of Sports Medicine recommends at least two strength training sessions "of a moderate intensity" each week. A workout should consist of eight to 10 exercises that condition the major muscle groups repeated eight to 12 times.

"To make significant improvements, particularly in inactive individuals, more moderate resistance activity works," Haskell says. As a rule of thumb, he advises his patients to spend about two-thirds of their exercise time in endurance exercise and one-third in resistance training and stretching.

Fitness Belief No. 5

Always see your doctor before starting an exercise program.

Depends on who you are.

The American College of Sports Medicine recommends that healthy men over 40 and healthy women over 50 who plan to start a vigorous exercise program first consult a physician. Younger people who have two or more risk factors for heart disease - such as high blood pressure or high cholesterol, or who are obese or smokers - should see their doctors first. And no matter your age, talk to a physician first if you have any cardiovascular, lung or joint or muscle condition.

Fitness Belief No. 6

Walking is the best exercise. No, swimming is. No, cross-country skiing is. . . .

The old saw is this: The best exercise is the one you'll do consistently. It's probably true for most of us.

Quickly, here's a rundown of the pros and cons of some popular aerobic exercises:

-- Walking: You don't need any special equipment, other than a decent pair of shoes. You can do it almost anywhere. You don't even have to work up a sweat. But it's not always easy to elevate your heart rate sufficiently when walking, especially if you're already quite fit.

-- Running: Almost as convenient as walking, except for the sweating part. Competitive runners have less body fat than any other group of athletes. However, running is not feasible for some people with joint problems, sometimes daunting for beginners, and not an especially good workout for the upper body.

-- Swimming: Works many muscles and has lower injury rates than running or cycling. But it's substantially less convenient for some. You have to find a pool. You have to get wet. You have to deal with your hair afterward. Also, there is conflicting evidence when it comes to weight loss. In some studies, swimmers lost weight; in other studies, their weight remained stable; and in still others, they gained weight (though usually the weight was muscle mass, not fat). The key seems to be the intensity at which you swim. If you're a slow swimmer, it's going to be more difficult to burn lots of calories than if you're a fast swimmer.

-- Aerobic dance: Can be done either at home or in a group, works all the major muscles and, if you're into it, is downright fun. Not good for those who aren't motivated by loud music and organized group activity. Pick your class, or tape, carefully and make sure it includes warm-up and cool-down times.

Fitness Belief No. 7

Carbohydrate calories won't make you fat; fat calories will.

As those of us who have made a habit of eating entire boxes of nonfat cookies have discovered, if you eat more calories than you expend, you gain weight.

That's not to say you should immediately start eating more fat, or that fats and carbohydrates are the same. The way the body absorbs fats and carbohydrates is different, says Jo Ann Hattner, a clinical nutritionist at Stanford and a spokeswoman for the American Dietetic Association.

Carbohydrates are simpler to digest, and so they enter the bloodstream as glucose more readily and are used by the body faster. Fat is more difficult to digest, and sticks around longer.

However, as Hattner points out, "A calorie is a calorie." You'll store extra ones as fat if the amount you take in exceeds the amount you expend.

Fitness Belief No. 8

If you stop exercising, all the muscle you built up will turn to fat.

Your muscles might get flaccid if you stop exercising. They may atrophy and be replaced by fat. But they won't turn to fat.

Still, "flaccid" doesn't sound so good.

Fitness Belief No. 9

It's better to lift heavier weights fewer times than it is to lift lighter weights many times.

Guess what. It depends.

Lifting a heavy weight fewer times helps build muscle strength. Lifting a lighter weight more times helps build muscle endurance. So, if your goal is to hoist your groceries out of the trunk, you want to build more strength.

If your goal is to hike six miles carrying those groceries, you want endurance.

Fitness Belief No. 10

You can never get too much exercise.

Let's face it: Most of us will never test this truism. However . . .

"The data and the literature that look at the number of days per week a person should exercise show three to five days per week is adequate to improve fitness and reduce risk of disease," says Weltman.

Still, for certain goals, more is better. If you're trying to lose weight, Weltman points out, more aerobic exercise means more calories burned.

There is a risk, however: You may perform the same kind of exercise to excess (see No. 3) and suffer an overuse injury.

"Some people think if hard is good, harder must be better," says Weltman. "And the way your body tells you that's not true is by injuring itself."

No pain, no gain?

Weltman sighs. "Typically, if you're in pain, you're doing too much."