MYTH: 'No pain, no gain'
A workout does not have to feel bad to do good. In fact, when you feel any pain during a workout -- not fatigue, but pain -- it's best to stop immediately. Pain signals that something is wrong, and ignoring the signal can result in injury. Soreness can be expected 24 to 36 hours after a tough workout but is not necessarily an indicator of progress.MYTH: 'Abdominal workouts burn the gut away'
Crunches and other "belly blasting" exercises will indeed build and strengthen abdominal muscles, but you'll never see the results if there's a lot of fat around your midsection. To have well-defined abs, you'll need to get rid of the fat covering the muscles. It's very difficult to target specific areas for fat-burning. Instead, launch an exercise regimen that reduces overall body fat, best achieved with a mix of aerobic exercise and a diet rich in fiber and lean protein. Once the fat burns away, you can admire the washboard ab muscles beneath.MYTH: 'Stick to your regimen'
We all tend to favor the exercises that come most easily, and as a result may make a habit of repeating particular routines. But as muscles accustom themselves to specific actions, they become more efficient at the exercise. A consequence of efficiency is energy conservation -- which means your body will burn fewer calories. The essence of cross-training, by contrast, is to work different sets of muscles, overcome weaknesses, and reduce the physical strains caused by repetition. To build more muscle and burn more fat, consider small but challenging modifications to your fitness routines.MYTH: 'A productive workout lasts about one hour'
It's a physician's job to help you set guidelines for the duration, frequency and intensity of your workouts, so don't hesitate to get your doctor's opinion before establishing a regimen. Health authorities, including the Mayo Clinic and the American Heart Association, suggest an exercise plan along these lines: If you're under 65 and in good health, try to engage in 30 minutes of moderate aerobic activity -- walking, swimming, riding a bike -- five days every week. Those capable of more rigorous conditioning should strive for at least 20 minutes of vigorous exercise, such as running or stair-climbing, three days per week, plus two days of strength training.MYTH: 'To burn more fat, work out on an empty stomach'
With all of the low-carb diets popular today, it's easy to forget that carbohydrates provide the body with fuel. The amount of carbs present in your system should be commensurate with the amount of energy you will expend in the short term. So, while a bowl of pasta before bedtime will leave you with an unhealthy surplus of calories, the same meal before exercising provides the energy needed to burn fat.The size and ideal timing of a pre-workout meal will vary from one person to the next. Start with small portions of carbs or carbs and protein about half an hour before exercise, then modify incrementally as needed. Smart choices include whole grains, fresh fruit, trail mixes of nuts and dried fruit, nutrition bars with about 5 grams of protein, and cereals with fiber.MYTH: Swimming provides all the exercise a body needs
Few fitness experts would argue against swimming. Our natural buoyancy permits low-impact movement, minimizing the stress and pounding associated with most other physical activity, and a good swim stroke employs all of the major muscle groups. A few laps in the pool make demands of the respiratory system that are terrific for increasing lung capacity, too. However, swimming is not especially effective in burning fat. Because a swimmer's body is supported by water, it doesn't have to work so hard against gravity as in land-based exercises such as running or lifting weights, and therefore fewer calories are burned. Swimming nonetheless remains an unparalleled aerobic exercise and helps prime the body for metabolizing fat effectively.MYTH: Treadmills are the equivalent of running outdoors
Convenience and personal preference are the factors that govern most runners' decision when choosing between a treadmill and an outdoor workout. Given a predominantly flat outside course, the exertion and weight-loss benefits are comparable; a treadmill set to a 1 percent incline makes up the modest difference. But several other factors come into play. When joint pain or injuries are of concern, the cushioned tread on a machine provides less impact than pavement or packed dirt, and the rotating tread further assists by sweeping your feet behind you. If you enjoy creature comforts while exercising -- temperature control, a television for entertainment -- a treadmill is a good choice. Still, the human body is optimized for being self-propelled through space, and anyone who enjoys a head-clearing run in fresh air finds it tough to beat. An outdoor run is generally better suited to natural movement, and terrain challenges, including downhill stretches (impossible to replicate on a treadmill), provide opportunities to burn extra calories.

Rich Maloof is an award-winning writer and regular contributor to MSN Health & Fitness. He has also written for CNN, MSNBC, NYU Medical Center and Women's Health, among others. His latest book was released in 2009 by St. Martin's Press. Enjoy more of Rich's work at www.richmaloof.com.