Better do more than just lose the fat.

It can be one of the most frustrating turns of events for anyone trying to shed those last few extra pounds--hitting a weight-loss plateau, where no matter how hard you try, you can't lose another ounce.

Surprisingly, the problem could be the way you went about losing the weight in the first place, says Phyllis Rogers in Over 40 & Gettin' Stronger: Gain Strength and Build Muscle as Fast as a 21-year-old. For every 10 pounds of weight you lose through dieting and cardiovascular exercise, three pounds of that total is muscle. And since each pound of muscle in your body burns 35 to 50 calories each day, you could be slowly decreasing the number of calories your body burns, eventually leading to a point where weight loss tapers off.

"It's a vicious cycle that's repeated over and over again by hundreds of thousands of Americans each year," Rogers says. Instead, she advises, incorporate a weight-training component to your workouts. Adding 10 pounds of muscle to your body will allow you to burn up to an extra 500 calories per day and break through that disheartening plateau.