Exercising but not losing weight?

We're asking why, when people get trim and fit through exercise, they often don't weigh any less than before. The answer is that muscle simply weighs more than fat.

Lean muscle tissue is 0.2 grams denser per cubic centimeter than fat, which means that when you replace fat with muscle through exercise you replace it with something denser and heavier. Laboratories use this difference in weight and density to estimate people's body composition. Using a method called hydrostatic weighing, researchers will weigh a person submerged in water and compare that number to the out-of-water weight. Someone with a high percentage of lean tissue will weigh more submerged since muscle is denser than water and sinks. Someone with a high fat content will weigh less underwater, since the less dense fat will float. For example, a muscular man of 5 feet 10 inches can easily weigh 180 pounds, while an out-of-shape man of the same height can weigh less because more of his bulk consists of fat.

Fitness experts are adamant about not looking to the scale to measure the successes of exercising. While muscle may weigh more than fat, it's a lot healthier to carry around. It's especially important to keep the most vital muscle, the heart, in shape. Plus, more muscles mean the body needs to burn more calories even while at rest to keep them fueled and fed, which leads to an increased metabolism.

Author of Fit or Fat, Covert Bailey is a fitness expert. Try his home body fat test at HealthCentral.com. Have a tape measure handy.

January 5, 2002

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