Body Composition Analysis at a Glance
Written by Mirco Joseph, CSCS, CPT, for Greenlight Long Island Magazine
Body Composition is the technical term used to describe the different components that make up a person's body weight. When analyzing body composition it is often convenient to think of the body as made of two components: fat and non-fat. The non-fat portion is usually called "fat free mass" or "lean body mass." Not all fat is bad; in fact some of it is essential. Our goal is to eliminate the unnecessary fat.
The so-called 'lean' tissues, such as muscle, bone, and organs are metabolically active, while adipose, or fat tissue, is not. Adipose tissue can be classified into three different categories:
A scale simply takes the sum of everything (fat, muscle, water, hair) and gives an absolute weight measurement. Scales can't determine the lean-to-fat ratio of that weight. An individual can be "over-weight" and not "over-fat."
Physiologists have developed several different methods of assessing the percent of fat vs. lean mass of an individual. These methods are referred to as Body Composition Analysis.
The standard for body composition analysis is hydrostatic weighing. Body composition analysis through immersion in water has long been the standard for measuring body fat. Fat weighs less than muscle. Fat and muscle each displace a known amount of water, and have a known mass. If you know how much someone weighs, then you can determine how much water they would displace if they were all muscle.
Hydrostatic weighing to determine body density, or hydro densitometry, is the accepted standard for measuring body fat.
Underwater weighing is the most cumbersome method of body fat testing, but it's also the most accurate. A subject sits on a scale in a tank of warm water, blows all the air out of the lungs and bends forward until completely submerged. The subject stays submerged for a few seconds while the underwater weight registers on a high precision scale. The result is then plugged into a mathematical equation. This test is repeated and the best results are averaged to get a very accurate reading of the amount of fat in the body.
For many years now, all tests are compared against hydrostatic for the sake of validity and margin of error. Hydrostatic results are considered absolute. For some more recent studies, three and four component tests, including hydrostatic weighing, bone density testing via DXA, lung capacity and residual volume testing, and body hydration testing are being used for even greater accuracy. These tests differentiate more components than just fat and lean-body-mass. They account for tissue hydration, and bone density, as well as eliminating error from lung, and intestinal contents.
Skin Folds Testing
The most common body fat test uses the skin fold caliper, a device that pinches your skin, pulling your fat away from your muscles and bones. You feel moderate discomfort, like when someone pinches your cheek.
Typically, the tester pinches three or four different sites on your body, such as your abdomen, arm and back. The thickness of each pinch is plugged into a formula to determine your subcutaneous body fat level.
Many things can go wrong with a caliper test. The tester may not pinch exactly the right spot, or may not pull all the fat away from the muscle. Or he may pinch too hard and accidentally yank some of your muscle. The calipers must exert a standard pressure and measure thickness to very small levels. Tests can vary greatly from tester to tester. Also, research shows 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. In addition, tests show this test is accurate for about 90% of the population, when using the appropriate formulas. Because of the consistency in results, the high percentage of people that this test is successful for, and the low margin of error, this is generally accepted as the best field test, outside of clinical testing such as hydrostatic, DXA and MRI.
Anthropometric measurement (girth and length) is a quick, easy and inexpensive method to estimate body composition. Using a standard calibrated cloth tape and a scale, your weight, height, and anywhere from two to four circumference comparisons are used to calculate your body fat.
This test is based on the assumption that body fat is distributed at various sites on the body such as the waist, neck and thigh. Muscle tissue, on the other hand, is usually located at anatomical locations such as the biceps, forearm and calf. There are a variety of formulas for this test, which vary excessively.
The YMCA test has been shown to be very inaccurate, whereas the ARMY test compares favorably to skin fold testing in 89% of the population. It has been shown to be inaccurate for women above 40 years old, elderly and very lean. Circumference testing is used in the military due to ease of testing, low cost, relative accuracy and lack of training requirement. When tests are marginal and are challenged, hydrostatic testing is normally used.
Bioelectrical Impedance Analysis (BIA)
Another common method of body fat testing is bioelectrical impedance. One may lie supine 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, because fat impedes the signal. BIA testing divides the body up into 'cylinders.' The arm, the torso, the upper leg, and the lower leg make up four separate cylinders for purposes of this test. The current flows through the body, finding varying resistance depending on the density of muscle, the amount of body fat encountered, and the hydration of your tissue. Bioelectrical impedance can have a huge margin of error, especially if the subject is extremely fat or extremely lean. Dehydration also can skew the results; the signal slows down, and you appear to have more fat than you really do.
The following rules must be followed to give any credence to the tests:
If you follow all of these rules you can get a pretty accurate reading.
Mirco Joseph is a Certified Strength and Conditioning Specialist and Certified Personal Trainer, as well as manager of the New York Sports Club in East Meadow, located at 625 Merrick Avenue. For more information, call 516.485.5100.