By Michael Scholtz, M.A., Best Life fitness expert

So many people start hitting the gym with one fitness goal in mind: To slim down a particular body part. By working a specific area extra hard, they hope to zap the jiggle on the belly, butt, or arms. But unfortunately, the idea of eliminating body fat from a certain area, often called spot reduction, is impossible. It's perhaps one of the most persistent myths in the field of health and fitness, but the truth is that there is no way to "zone in" your weight loss on one area or tighten the skin by exercising a particular body part.

From a physiological standpoint, when you work a particular body part you "tone" that area. Toning is basically improving the ability of a muscle to hold its shape. It can give muscles a nice tight, taut look, but only if you're also losing body fat at the same time. If you don't lose the fat that sits on top of the muscle, you'll never see that muscular definition.

Of course, to lose body fat you have to consume fewer calories than you expend—and exercise is an important factor in this equation. But there's no way to control where the body will lose fat from first—in fact, you lose it from all over the body at different rates. Some body parts lose fat faster, and this is largely determined by gender and genetics. For example, many women gain in the hips and thighs first and typically lose from those areas last.

But there are big-time benefits to building muscle even if you can't see the results right away. The more muscle you have, the more calories you'll burn—even when you're just vegging out. That's because it takes more energy for the body to maintain muscle tissue than it does fat. Plus, strength training reduces your risk for osteoporosis and helps improve your functional fitness, or your ability to do the lifting, twisting and balancing required for everyday activities.

The keys to losing fat and revealing those toned, strong muscles are to eat a healthy, balanced diet and to follow a fitness plan that includes both cardio (to burn calories) and strength training (to tone muscles and keep your metabolism humming). Stick with your diet, aerobic and resistance training, and those problem spots will be a distant memory.

The Seduction of Spot Reduction, and other weight-loss and fitness tips from Bob Greene, Oprah's trainer.