Don’t let one of these muscle misconceptions come between you and a calorie-burning, body-sculpting workout

By Shape Editors
January 14, 2013

After diet, there's nothing more rampant with myths, half-truths, and downright falsehoods than exercise-especially its effect on weight loss. Follow any of this inaccurate advice, and you may wind up wasting time, energy, and money, or even injuring yourself.

No need to bust out a lie detector, though. Jason Greenspan, an ACE (American Council on Exercise)-certified personal trainer and founder of Practical Fitness & Wellness, identified the seven most common, persistent misunderstood notions about fitness-and offered the honest truth to help you build a strong, lean body.

Myth: Muscle "weighs" more than fat.


Reality: A pound is a pound is a pound-unless you're defying the laws of physics. No substance weighs more then another one unless it actually weighs more. Simply put: One pound of fat weighs the same as one pound of muscle. "The difference is that fat is bulkier than muscle tissue and takes up more space under the skin," Greenspan says. In fact, one pound of fat is roughly the size of a small grapefruit; one pound of muscle is about the size of a tangerine. But that tangerine is active tissue, meaning that it burns more calories at rest than fat does.

Myth: Weight training converts fat to muscle.


Reality: This is physically impossible, Greenspan says. "Fat and muscle tissue are two completely different substances. Exercise such as strength training will help to build muscle, which encourages fat loss by increasing your resting metabolism so you can burn more calories throughout the day." To get a lean look, you need to build muscle through weight training while simultaneously losing fat-but one doesn't magically become the other.

Myth: Lifting heavy weights will cause women to bulk up.


Reality: We just don't produce enough testosterone, the male sex hormone that spurs muscle growth, to get big, meathead muscles. Lifting weights sometimes gets the blame for adding bulk because if you haven't yet shed extra body fat, it can give the illusion that you're getting larger, Greenspan says. But muscle boosts your metabolism, so don't be afraid of those 20-pound dumbbells (or at the very least, work your way up to them).

Myth: You can walk off extra pounds.


Reality: Although walking is good exercise and most Americans don't do enough of it, if you want to lose a noticeable amount of weight, it's not the best method since it's low intensity and doesn't burn a lot of calories during or afterward. To substantially shrink your belly and keep it flat, Greenspan says you want an integrated approach of strength training, cardio (preferably intervals), and a calorie-controlled diet. Adding in a few extra miles on your feet daily as one part of an overall weight-loss plan is good and good for your health, but that alone probably won't lead to significant results on the scale.

Myth: You'll burn more fat on an empty stomach.


Reality: The body torches about the same amount of flab whether or not you nosh before a workout, Greenspan says. But your body also needs fuel in order to perform at its best, build muscle, and burn calories, so you should always eat something light about 30 to 45 minutes before exercise such as a protein shake, yogurt, or a piece of whole-wheat bread with peanut butter.

Myth: You should do cardio and strength on separate days.


Reality: According to Greenspan, there is no scientific reason to keep the two isolated, and you up your chances of hitting your goal-whether it's health, strength, or a pants size-by combining them. And then there's that whole time-saving perk. Greenspan suggests doing a circuit where you alternate between combo exercises (squat to row or press, for example) and short, high-intensity cardio bursts (such as sprinting on the treadmill). Going back and forth like this with minimal rest builds strength and gets your heart rate up even more than a typical half hour on the elliptical or Stairmaster at moderate pace.

Myth: Long and slow cardio training burns the most fat.


Reality: While it's true that lengthy, slow workouts will use up more fat for energy, they're not the way to go for fat loss; instead focus on the total calories burned during and after your workout. Ditch devoting 75 mind-numbing minutes to a slow trod on the treadmill, and do interval training or higher-intensity exercise for half-or even a quarter-of that time, which kills more calories at a faster rate and keeps your metabolism revved post-gym sesh.