When assessing your level of fitness, it is helpful to determine your body composition — how much of your body is composed of fat and how much is composed of everything else. Your body composition is also called your body-fat percentage. If you score a 25 percent on a body fat test, this means that 25 percent of your weight is composed of fat.
You should consider your body-fat percentage in context with other health measures, such as your cholesterol levels, blood pressure, resting heart rate, and other gauges of fitness.
Although body fat testing has its limits, your results can give you great insight into how your fat-loss and exercise program is coming along. For example, a body-fat test can tell you that a 7-pound weight loss means that you lost 10 pounds of fat and gained 3 pounds of muscle.
Here’s a look at some methods of measuring your body fat:
Pinching an inch: This body-fat test uses the skinfold caliper that pinches your skin, pulling your fat away from your muscles and bones. Typically, the tester pinches three to seven different sites on your body, such as your abdomen, the back of your arm, and the back of your shoulder. The thickness of each pinch is plugged into a formula to determine your body-fat percentage.
Your tester should pinch each site two or three times to verify the measurement.
Credit: "IMG_1624," © 2010 , skamille used under a Creative Commons Attribution 2.0 Generic license: http://creativecommons.org/licenses/by/2.0/legalcodeTaking your measurements: You don’t get a body fat percentage by taking your measurements, but you can use the numbers to keep track of inches lost (or gained, if you’re trying to pack on muscle), which can be motivating in and of itself. If you’re losing inches, chances are, you’re dropping body fat.
Some common places to measure include across the middle of your chest, the center of your upper arm, the smallest part of your waist, the widest part of your hips, the widest part of your thigh, and the widest part of your ankle.
Getting dunked (underwater weighing): Underwater weighing is the most cumbersome method of body-fat testing, but it’s also the most accurate method that’s anywhere near affordable. You sit on a scale in a tank of warm water about the size of a Jacuzzi.
Then you blow all the air out of your lungs and bend forward until you’re completely submerged. You stay submerged for about five seconds while your underwater weight registers on a digital scale. The result is then plugged into a mathematical equation.
Bioelectrical Impedance Analysis (BIA): For this method, you lie on your back while a signal travels from an electrode on your foot to an electrode on your hand. The slower the signal, the more fat you have.
This is because fat impedes, or blocks, the signal. The signal travels quickly through muscle because muscle is 70 percent water and water conducts electricity. Fat, on the other hand, is just 5 to 13 percent water. Similar technology is used in body-fat scales and handheld gadgets that are less accurate than BIA.
Dual-Energy X-ray Absorptiometry (DEXA): Not only does this method measure how much fat you have, but it also determines where the fat is located on your body, a more relevant health indicator.
Originally developed to scan bone density, DEXA is available at hospitals and in doctors’ offices; it usually requires a physician’s referral. You lie on a bed while low doses of two different X-ray energies scan your body from head to toe.