4 Reasons Calipers Fail to Give Accurate Body Fat Results

There are a lot of great things about calipers. Many brands of calipers are relatively inexpensive, they’re portable, and they offer you a better picture of your overall health and fitness than by simply standing on a scale. Because calipers operate by physically pinching your outside skin, they’re also a reliable way of measuring body fat change over time.

However, their convenience is also the main component behind their drawbacks. If you are using calipers to measure your or someone else’s body composition, you should be aware of the following:

#1: The results are heavily influenced by how accurately skinfold sites are located

There are several different methods to perform a caliper test, but one of the more accurate versions is the 7-site test using the Jackson and Pollock equation for body density. The 7 sites are shown here:

Each of these sites must be located precisely, and an X should be drawn in the location to ensure proper caliper placement.  You can’t just eyeball a location; if accuracy is important to you, you must take the time to use a tape measurer to locate each site. The abdominal site, for example, is 2 cm to the right of the belly button.

If the person performing the test has not been trained appropriately, or if two different people perform a test at different times on the same person, the chances of getting an accurate measurement drop significantly. 

#2: Perfect Technique is Key

Accuracy in locating each site is just the first step; there are still difficulties even if a site is located precisely. According to the Center for Disease Control’s guidelines for caliper use, not only are there guidelines for locating each skinfold site, there are variances between how the calipers must be placed on each skinfold. These can be only properly placed if each site is marked with an X. However, just placing the X is only half the challenge.

For example, when pinching the subscapular (shoulder blade) site, the top caliper jaw must be placed directly on the X mark. This is in contrast with how the caliper must be placed for the tricep pinch; in this case, the both jaws must be placed on either side of the X. If these small but critical procedures are not followed, accuracy may drop.

Proper technique extends beyond handling the calipers. For instance, the CDC’s guidelines dictate that a caliper reading can only be taken after pinching, holding, and waiting for three seconds. This allows the skin to compress properly for an accurate reading. Taking a reading immediately after pinching can distort the results.

#3: Caliper Results Take Empirical Estimations Into Account, Particularly Age

Calipers use the sum of skinfold measurements to report body fat percentage. But in order to turn the measurements into a percentage, two equations need to be used - one to calculate density and one to change density into body fat percentage.

The Jackson-Pollock Equation is frequently used to measure body density and is typically the first step to determining body composition using calipers. The equation looks like this (emphasis added):

Body Density = 1.112 - (0.00043499 x sum of skinfolds) + (0.00000055 x square of the sum of skinfold sites) - (0.00028826 x age)

Notice how age acts as a variable in the equation. This is a deliberate insertion intended to adjust and increase the equation’s accuracy.

However, by accounting for age, the Jackson-Pollock Equation makes inherent assumptions about the effect age may have on body density, which ultimately influences the final body fat percentage result. These assumptions can misrepresent people who fall outside of normal ranges for their age. 

Consider a 50-year-old man, who is relatively nonathletic. By age 50, this man will have lived more than half his life, have adopted a certain lifestyle, and will have a body composition reflecting it. 

Now consider the same man, but assume that he has been more physically active for the entire duration of his life. His body composition will be quite different. His skinfold measurements will obviously be different as well. However, regardless of the skinfold measurements or relative athleticism, both versions of this man will be subject to the same adjustment for age, which will skew the accuracy of the results towards what is considered average for a 50-year-old man. 

This means that in our example, the very fit and athletic 50-year-old man may have his body fat percentage overestimated because he likely falls outside the average for his age group.

#4 Caliper Equations Also Make Assumptions About Body Fat Distribution

Calipers only directly measure the width of skinfolds; they rely on equations to take this data and turn it into meaningful body fat percentage results. In order to do this, certain assumptions about body fat have to be made, such as how much body fat is due to subcutaneous fat and how much is due to visceral fat.

These assumptions can be quite large. According to one source, 90% of fat is subcutaneous “in most people.” However, statements like these can be problematic because they do not define what “most people” or even “normal people” are. People may consider themselves to be included in “most people,” when they actually fall outside the expected (and undefined) ranges. 

The reality is that true proportions of subcutaneous fat to visceral fat can range significantly in individuals, depending on a multitude of factors including age, gender, ethnicity, and lifestyle. 

Although widely used, the Jackson-Pollock Equation was developed in the 1970s. Since that time, obesity levels have risen dramatically, doubling between 1980 and 2000. According to the International Journal of Body Composition, this poses a problem concerning the effectiveness of the Jackson-Pollock equation’s ability to produce reliable body density results for modern adults today. The writers argue (emphasis added),

There can be little doubt, the Jackson and Pollock body fat equations for men, and the Jackson et al. equations for women are both accurate and valid methods of estimating body fat (%) for subjects taken from a representative population of adults observed during the 1970s. However, a representative population of  adults in the 21st century will be considerably heavier and fatter.

If we examine the consequences of using the Generalized Body Density equations recommended by Jackson and colleagues to predict the body fat of overweight or obese subjects from today’s population, there is a  serious danger of under estimation.

For some people, particularly those who are overweight, relying on this equation may not give a truly accurate result for body fat percentage. And because calipers use this equation, the best they can do is provide an estimation, and a potentially unreliable one at that. 

But when you’re taking your health seriously, why would you accept an estimation?

Alternatives

Fortunately, advances in technology have made finding precise body fat percentage and body composition results much less problematic, which makes relying on calipers less necessary. 

For starters, hydrostatic weighing and DEXA scans are both regarded as gold standards to determine body fat percentage/body composition, although securing access to one of these tests isn’t always the easiest or financially feasible.

Among the most convenient and quickest methods to determine body fat percentage are devices that use bioelectrical impedance analysis (BIA). Although these devices are far more convenient than either of the gold standard procedures, they can range widely in quality and accuracy.

Due to the wide range in quality, the need for precise, medically reliable body fat percentage tests has led to the rise of extremely high quality BIA devices. These devices employ advanced technology that allows for precise results without any of the inconvenience of the gold standard procedures. They also eliminate some of the drawbacks of calipers, such using empirical estimations or the need for hours of practice and experience to perform a test properly. 

Hopefully this helps you understand a little more about the potential use of calipers. Although they can be so quick and simple to use, they do have significant drawbacks when accurate results are essential.

But shouldn’t accurate results always be essential?

RYAN WALTERS | AUTHOR

RYAN IS A DIGITAL MARKETING SPECIALIST AT INBODY USA. HAVE QUESTIONS? YOU CAN REACH OUT AT [email protected].