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Reference Guide to Body Composition

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

-- By Jen Mueller and Nicole Nichols, Fitness Experts
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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
Nicole was named "America's Top Personal Trainer to Watch" in 2011. A certified personal trainer and fitness instructor with a bachelor's degree in health education, she loves living a healthy and fit lifestyle and helping others do the same. Her DVDs "Total Body Sculpting" and "28 Day Boot Camp" (a best seller) are available online and in stores nationwide. Read Nicole's full bio and blog posts.

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Member Comments

  • This and related articles are fine as far as they go. But they are dated and do not go far enough. For example, the World Health Organization recommends an optimal BMI range for HEALTH AND LONGEVITY of 22-18.5 which is based on thorough statistical analysis of mortality and medical cost records.

    This article offers no reasons for targeting any specific body composition. After all, without a target, why consider body composition at all? Additionally, it misses the best body composition method: MRI which is the most accurate and detailed and provides pictures of exactly where body fat is located. Fat location has important health and longevity implications because visceral adipose tissue is a marker for a number of potentially fatal diseases.

    This article needs to be updated. - 4/2/2013 7:28:46 AM
  • This is the best explanation of accurate weight calculations, including BMI, that I have seen in some time. Although it does not account for "shrinkage" as we age (therefore, height and weight may be inaccurate, since the appearance of "body fat" may be in the midsection due to spinal compression), it clearly details the different methods for calculation of accurate weight for height and body habitus. Thank you. - 6/13/2011 12:58:54 PM
  • Now THIS is a thorough discussion of the benefits and problems with various ways to estimate % body fat:

    http://forums.j
    pfitness.com/
    fat-loss/4262
    6-pitfalls-bo
    dyfat-testing.html

    Interesting that unlike other sources I've read he concludes that DXA is about the same accuracy as hydrostatic weighing. - 3/30/2011 12:44:58 PM
  • Bod Pod is like underwater weighing but less accurate due to the difference in density between water and air. It has all the same sources of error and then some. It's better than no measurement. But circumference measurements are probably better tracking than anything but DXA for most people. - 3/30/2011 12:13:00 PM
  • You really need to update this article to include a reference to DXA body composition scans.

    http://en.wikip
    edia.org/wiki
    /Percent_body
    _fat#Dual_ene
    rgy_X-ray_absorptiometry - 3/30/2011 10:30:22 AM
  • I was wondering about the BodPod machine. I heard that is very accurate. Would like to know more. - 8/30/2010 1:35:47 PM
  • I am reading the book "Racing Weight" by Matt Fitzgerald and he talks about DEXA scanning being a highly accurate way to measure body fat percentage. Before reading this book, I didn't know that. I'm wondering why this method is never mentioned by SparkPeople and not in this article. Getting a DEXA scan can be covered by insurance. - 8/6/2010 4:31:10 PM
  • I've been using a combo of DXA scans every six months and a home body composition scale that's consistently off by the same % (or at least according to the 3 scans I've had done).

    My BMI is normal, now to get the fat down too. - 1/26/2010 5:43:53 AM
  • CLOA513
    Here is link for the DXA body composition mentioned by DEXARED.
    They don't mention the X-ray dose you surely must get with such a scan. Its the cumulative dose that matters so add many DXA scans and some normal X-rays and high community exposure and it would have a significant risk of cancer effect.

    http://www.tope
    ndsports.com/
    testing/tests
    /DEXA.htm - 11/15/2009 10:51:55 PM
  • You can do an easy test in the pool. It is a measurement done for scuba diving and I found it really interesting. Go to the deep end in the water. Take a deep breath and then keep your body upright. A "neutral" body will float with the water at eye level. A body with a lot of fat will float with the water below eye level (for me at my mouth). A body with a lot of muscle will float (or not) below eye level. Of course there are lots of factors like water density that can change the results but I was amazed in my class how quickly they decided what weights people needed to be "neutral" in the water. Cost - admission to a pool. - 8/18/2009 10:01:36 AM
  • DEXARED
    I am disappointed that you made no mention of DXA (dual energy x-ray absorptiometry) in your analysis of the various body composition methods. This is a very easy, quick and precise way to determine fat and lean mass. The person is measured from head to toe and is a very good way to follow weight loss from one time to another visually showing the entire person. None of the other methods show you an image. This is used by many of the most prestigeous universities and research studies in the country. You missed a very important piece to an otherwise very thurough article. - 7/1/2008 3:28:45 PM
  • Great article. - 6/1/2008 11:37:35 PM
  • I had been wondering why the hand held bioimpedance machine that we use at worked shows my body fat as 15% or more less than what my scales at home say. I certainly have more fat in the lower half of my body, so if that is all my scales are measuring, of course it would be higher, than a machine that is only testing the fat in my arms. So do I average the two to get a more accurate number of my body fat?!lol - 5/12/2008 8:33:41 PM
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