Fitness Articles

Reference Guide to Body Composition

An In-Depth Look at Body Fat, BMI and More


Accuracy: The American College of Sports Medicine states that skinfold measurements, when performed by a trained, skilled tester, are up to 98% accurate. Because of the consistency in results, the high success rate, and the low margin of error, this is generally accepted as the best field test, outside of clinical testing, such as hydrostatic weighing (see below).

Limitations: The estimation results obtained from skinfold measurements vary widely from technician to technician. The "art" of skinfold measurements requires the technician to properly identify a site measurement and pinch the skin gathering only the fat store and no other tissue. If the tester does not pinch exactly the right spot, or pull all the fat away from the muscle, the test will be inaccurate. When skinfold calipers cannot open wide enough to measure the total fat thickness, this technique tends to grossly underestimate body fat percentage in the obese population. In addition, some people can best be described as “hard to pinch,” meaning that it’s difficult to pull their skin and fat away from their muscle and bone. Test results will be less accurate for these individuals.

The wide variety of equations (number and location of sites tested) reflects the problem with the accuracy of this method. When getting retested, it’s wise to have the same professional who conducted your initial assessment measure you again for consistency.

Bioelectrical Impedance

What it is: Bioelectrical impedance is a weak electric signal that goes through the body to measure body composition. A small 500-800 micro-amp (50 kilohertz) signal measures the body's ability to conduct the current.

What it measures: These tests estimate a person’s body fat percentage.

How it works: A special scale or handheld device sends a weak electrical signal through into the body. This current flows through the body, finding varying resistance depending on the density of the muscle, the amount of body fat encountered, and the hydration of the tissue. The slower the signal (measured in ohms), the more fat is present, because fat interferes with the signal. The faster the signal moves, the more lean (muscle) tissue is present, because lean tissue is highly conductive due to its high water content.

Along with other variables that you input into the device (such as gender, age, weight and height), the machine will estimate your body fat percentage based on the speed of the traveling signal.

Where to find it: Bioelectrical impedance testing is pretty common these days. You can buy your own handheld body fat testing device online or at the store, as well as special scales that use bioelectrical impedance to calculate your body fat percentage in addition to your weight. Both of these devices are often used in commercial and health care setting as well. Gyms and universities offer these tests, but prices can range from free to $30 or more per test. Home machines (handheld and scales) can be purchased for anywhere from $50-$400.
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About The Author

Nicole Nichols Nicole Nichols
A certified personal trainer and fitness instructor with a bachelor's degree in health education, Nicole loves living a healthy and fit lifestyle and helping others do the same. Nicole was formerly SparkPeople's fitness expert and editor-in-chief, known on the site as "Coach Nicole." Make sure to explore more of her articles and blog posts.

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