You've probably heard of fad diets — for instance, eating nothing but grapefruit for a month to lose 10 pounds. The fitness world has plenty of fads, too. Even the most fitness-savvy can be duped by fitness fiction. When the media reports misleading information, it can spread like wildfire before being disputed by fitness experts. Trouble is, once a rumor gets out, it's hard to squelch.

Following outdated or unproven fitness advice may keep you from getting the maximum benefit from your fitness routine. You may even do yourself more harm than good. Here's a look at some common misconceptions.

Fitness fibs

Go for the burn. Remember that saying, "No pain, no gain"? Not true. Exercise shouldn't hurt. A little muscle soreness when you do something new isn't unusual, but soreness doesn't equal pain. You don't need to make your muscles burn to know they're working. If it hurts, stop doing it.

Aerobic exercise is all that matters. Not true. In fact, a good, balanced exercise program includes flexibility training (stretching) and strength training.

Women who strength train will bulk up. Your goal isn't to become a bodybuilder — you just want to improve your strength and muscle tone. But you don't want the bulky look of pumped-up muscles. Don't worry. Women generally don't have enough testosterone — the hormone that can develop bulky muscles in men — to make that happen.

Exercise has to be strenuous to be beneficial. You don't have to push yourself to extremes to get the benefits of exercise. In fact, if you exercise excessively, you run the risk of overtraining. Alternate hard workout days with easier ones. And don't forget to rest. Take two to three days off or perform less intense exercise — for example, walk instead of jog or run — to recuperate from especially difficult activities.

Going to a gym is the only way to get fit. Not so. Any movement is good. You can fit a considerable amount of physical activity into your life by doing things you enjoy. Dance, ride a bike or take a brisk walk on a nature trail. Plan a home workout using a fitness tape. Lift some hand weights or water jugs while you watch your favorite TV show. It all counts. And if you're short of time, break it down. Walk for 10 minutes, three times a day, and you'll get the health benefits of a 30-minute walk each day.

Abdominal exercises will flatten your stomach. Sorry. Abdominal exercises, such as sit-ups (crunches), are important for strengthening those muscles and improving posture. But muscle is muscle and fat is fat. If you have excess fat in your abdomen, you won't be able to see the muscles, no matter how many crunches you do. There's no such thing as spot reducing — losing weight in one specially designated area. To lose fat, you need to eat fewer calories than you burn. In short, strive for a healthy weight.

Aerobic exercise will help you lose weight by speeding up your metabolism. Not entirely true. Your metabolism — the rate at which you burn calories — does speed up during your workout and may remain elevated for a short time afterward. But it doesn't stay that way all day. You won't more efficiently burn the calories from a double cheeseburger, fries and milkshake later that evening. However, if you add strength training to your aerobic workout, you'll build calorie-burning muscle, which will magnify your metabolic benefits over the long term.

Exercise makes you hungry. Fortunately, the opposite can be true. Intense exercise actually can suppress your appetite, at least for a while. Exercise also helps you control your appetite by making you more aware of how your body feels. You can focus on giving your body only what it needs — not more than it needs.

You can eat whatever you want if you exercise enough. Not true. If you eat more calories than you burn off in a day, you'll gain weight. A good fitness regimen includes a sensible balance between getting enough exercise and eating right.

Exercise keeps you up all night. As long as you don't exercise within three to four hours of your bedtime, the opposite is true. Exercise contributes to a more restful sleep and makes you more alert in your daily life.

By using hand and ankle weights while you jog, you can do strength training and aerobic conditioning at the same time. If you want aerobic exercise, then jog. If you want strength, then use resistance exercises. Don't combine them. The momentum that weights generate when you perform aerobic activities can stress tissue and lead to joint and muscle problems.

The sure bet

No magic pill or miracle-working exercise device will help you with your fitness goals. The truth is you have to be dedicated, and that takes hard work. Be wary of gimmicks or fads.