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During any physical evaluation, you'll probably be weighed. Just know that your weight is of limited value. When you hop on a scale, you learn the grand total weight of your bones, organs, blood, fat, muscle, and other tissues. This number can be misleading because muscle weighs more per square inch than fat.
Consider two men who stand 5'8" and weigh 190 pounds. One guy may be a lean bodybuilder who has a lot of muscle packed onto his frame. Another guy may be a couch potato whose gut hangs 4 inches over his belt buckle. Even a low weight doesn't necessarily indicate good health or fitness. It may simply mean that you have small bones and little muscle.
More helpful than your body weight is 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 fat test, this means that 25 percent of your weight is composed of fat.
Like your weight, your body-fat percentage is not necessarily a measure of your health. True, cardiovascular disease, diabetes, and certain cancers are more prevalent among overweight people — men who have more than about 20 percent body fat and women who have more than about 30 percent body fat. However, some researchers believe that these health problems are not caused by the extra fat itself but rather by a lack of exercise and a poor diet. In other words, if you exercise regularly and eat well, extra body fat may not compromise your health. So consider your body-fat score in a context with other health measures, such as your cholesterol levels, blood pressure, and other gauges of fitness, such as a submaximal test and your resting heart rate.
An additional number to consider is the circumference of your waist. Excess abdominal fat — the type that lies deep in your belly, clumped around your organs — is linked to increased risk for heart disease. Heavy thighs, on the other hand, do not appear to be related to health problems. (In other words — to use terms we can all relate to — a beer belly is more harmful to your health than saddlebags.) Men with waist measurements greater than 40 and women with waist measurements greater than 35 should consult a physician.
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. Sure, your scale can tell you that you lost 7 pounds. But a body-fat test can tell you that your 7-pound loss means that you lost 10 pounds of fat and gained 3 pounds of muscle, results that are probably more motivating.
Body-fat testing also can tell you if you have too little fat. Maybe you can never be too rich, but you definitely can be too thin. For women, super-low body fat — below about 16 percent — may lead to problems such as irregular menstrual periods, permanent bone loss, and a high rate of bone fractures.
 | Keep in mind that every body-fat testing method has room for error. You may even get wildly different readings using the same test, depending on the skill of the tester or the condition of the equipment. |
The only way to measure body fat with complete accuracy is to burn yourself up and take a carbon count of the ashes. Because that technique doesn't draw too many volunteers, scientists have developed a number of other methods. Here's a look at the ones you're most likely to come across.
Pinching an inch
The most common body-fat test uses the skinfold caliper, a gizmo that resembles a stun gun with salad tongs attached. When your tester fires, the tongs pinch your skin, pulling your fat away from your muscles and bones. (You feel moderate discomfort, like when your great aunt pinches your cheek on the holidays.) 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.
 | Many things can go wrong with a caliper test. The tester may not pinch exactly the right spot, or he may not pull all the fat away from the bone. Or he may pinch too hard and accidentally yank some of your muscle. Also, research suggests that certain formulas are more accurate for certain ethnic groups, age ranges, and fitness levels. |
| Experts give this test a margin of error of four points, meaning your actual body-fat percentage could be four points higher or lower than it actually is. Be sure to get tested before your workout. When you exercise, blood travels to your skin to cool you down. This can cause your skin to swell, and you may test fatter than you really are. Plus, calipers can slip if your skin is wet from sweat. |
If you want to try this method on your own, you can purchase calipers such as Accu-Measure (available for about $20 through Collage Video). These calipers come with a decent booklet that explains how to test yourself and interpret the results. For better accuracy, you may want to have a friend perform the test on you.
Taking your measurements
A less precise but also helpful way to keep track of your body fat is to take your measurements. You don't get a percentage, 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. You can write these numbers on the chart at the end of this chapter.
Getting zapped (also body-fat scales and handheld testers)
Another common method of body fat testing is called bioelectrical impedance analysis (BIA). 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 resemble a car steering wheel and are even less accurate than BIA.
| Bioelectrical impedance can have a huge margin of error, especially if you're extremely fat or extremely lean. In one study, world-class female distance runners were found to average 20 percent body fat, when more reliable methods actually show that they were closer to 10 percent. Dehydration also can skew the results wildly; the signal slows down, and you appear to have more fat than you really do. Don't drink alcohol or caffeine for at least 24 hours before the test because they can lead to dehydration. |
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 comes the unnerving part: You blow all the air out of your lungs and bend forward until you're completely submerged. If there's air trapped in your lungs, you score fatter than you really are. Knowing this fact makes you try really, really hard to blow out your air, which makes you feel like you're about to explode. 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.
This method of testing is based on the premise that muscle sinks and fat floats. The more fat you have, the more your body wants to float when dunked under water. The denser you are, the more you sink, and the more water your body displaces.
The margin of error for this test is 2 to 2.5 percent for young to middle-aged adults. The results are less accurate for children, older adults, and extremely lean people. This is because lean body tissue is made up of other things besides muscle. Bone, for example, isn't fully formed in children, and it may be somewhat porous in older adults and somewhat denser in super-fit people. You can get this test done at sophisticated sports-medicine clinics or labs for $50 to $100.
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