How can I improve the accuracy of taking skinfold measurements?

Follow these four general suggestions:

1. Avoid taking measurements immediately following light to more intense exercise or physical activity. Fluid loss (even slight dehydration) forces fluids from the tissues below the skin, decreasing the thickness of skinfolds. 
2. Check that the body regions where you are going to measure skinfolds are free of body lotions—moist skin makes it difficult to grasp the skinfold.
3. Read the caliper value with your eyes focused directly on the value, not by viewing the caliper from the side (called parallax—similar to reading a speedometer from the passenger seat).
4. When making a second set of “after” measurements, take the skinfolds about the same time of day as you did for the first or “before” measurements. If you recorded the first set of skinfolds at 9AM, also take the second set of “after” measurements at 9AM. Hydration varies during the day, so even identical technique can produce differences in skinfolds due to differences in hydration among morning, afternoon and evening measurements.

Should the skin area be marked before taking skinfold and girth measurements?

Yes. This is a general recommendation for individuals without experience in anthropometric assessment techniques. Marking the anatomic locations can be discontinued once a person has tested a minimum of 30 individuals and reliability of measurement is high (reliability exceeds r = 0.85. Use a felt tip pen to pinpoint more exact skinfold and girth anatomic locations. Make a small dot on the skin surface, and use that dot as an anchor or reference point. In the photo below, we have placed a small red dot at the midpoint of the fold, with the calipers placed in line with the dot.

You would use this same procedure for all skinfold sites. An alternate method uses a small cross at the center point (two perpendicular lines that represent vertical and horizontal). We prefer the dot method because your eye will automatically align the tips of the caliper to grasp either a vertical, horizontal, or oblique fold. For skinfolds, grasp the skinfold on either side of the fatfold with your thumb and forefinger. The width of the opening between your thumb and index finger should feel natural”— not squeezed too close together nor too wide. The thumb and forefingers should remain parallel to one another. After you grasp the fold, lift (pull) the fold away from the underlying tissue. Place the caliper tips to the side of the fold, about one-half inch below your fingers, and then read the caliper value within three seconds. For the girth measurements, use the small dot(s) as anchor points, and place the cloth tape in-line with the dot(s). This should provide reference points for placing the tape firmly on the area. Pulling the tape too tightly compresses the skin and will give a smaller than normal girth value. All of the girths except those on the arm should be measured in a line parallel to the floor.

Why must the skinfold value be read within three seconds?

Little or no compression of fluid beneath the skin occurs within this brief interval. Thereafter, the pressure of the caliper tips against the skin “forces” fluid from the area, creating a lower than normal skinfold score.

Why is it important to calibrate the skinfold caliper?

All measuring devices, including the most sophisticated apparatus, have a certain amount of inherent “error.” The problem is not identifying what type of error exists (technological or human), but not identifying how much error exists. You can make a correction for any error if you know how much error exists. For example, what is the exact width of a piece of paper? If the manufacturer certifies the width as 8.5 inches, then the ruler you use to measure the width should measure exactly 8.5 inches. What if it does not? There are two possibilities: (1) either the ruler is in error, or (2) the ruler is correct but the width of paper is not 8.5 inches. How could you find out the “truth” about the width?One answer is to use a precise device like a laser or other instrument certified for its precision to measure the ruler’s accuracy. Consider a distance of 8.5 inches measured by the laser device. Then use the ruler to measure 8.5 inches. If there is no discrepancy and the ruler measures a distance of exactly 8.5 inches, no “correction” factor need be applied. If needed, a correction factor adjusts the discrepancy so it equals the “true” distance. Thus, if the ruler measures only 8.25 inches, a 0.25 inch correction factor would make the accuracy of the ruler equal to the laser measurement. Calibration refers to the process of adjusting an instrument like a ruler or skinfold caliper for its inherent error compared to an established standard like a laser ruler or atomic clock. Thus, a skinfold caliper requires calibration to ensure that when it measures 15 mm for the triceps skinfold, for example, the tester (and client) can feel confident in the accuracy of this measurement.

How can I calibrate the skinfold caliper?

A caliper can be calibrated by comparing its measurements against a standard or “calibrator.” The BodyImage Kit™ includes a small, plastic calibrator that can check the accuracy of the calipers’ jaw openings from 10 to 50 mm. The manufacturer has certified that each of the distances on the calibrator has an accuracy of 0.025 mm. Thus, using the calibrator to verify the accuracy of the calipers’ jaw openings determines if a discrepancy occurs between the caliper reading and the known distance using the calibrator. If the caliper does not require calibration, the measured skinfold thickness reflects the true distance of that measurementTo calibrate the skinfold caliper, measure the distance of each saw-tooth opening with the skinfold caliper. Each of the saw-tooth openings equals 10 mm. Thus, if you measure the first opening and the caliper reads 11 mm (when it should read 10 mm), you must subtract 1 mm from any skinfold score within the range of 10 mm. Similarly, if the discrepancy equals 1 mm for the other saw-tooth measurements, you would subtract 1 mm for each skinfold measured. In contrast, if the caliper reads only 9 mm when you measure the saw-tooth distance, you must add 1 mm to the skinfold reading. As an example, suppose you calibrate the skinfold caliper by measuring the distance of each saw-tooth distance. You find that only the 30-40 mm distance has a discrepancy of +1 mm (it reads 41 mm instead of 40 mm, but is right on for the other measurements). Knowing this information about the caliper, you must make an adjustment to the persons skinfold score by 1 mm. In this case, you subtract 1 mm from the measured skinfold score. Thus, for a measurement of 37 mm for the iliac skinfold, the client’s actual score would be reported as 36 mm.

How can I calibrate the girth tape?

The assumption is made that each succeeding distance on the cloth tape reflects a true distance represented by the marking printed on the tape. A minor discrepancy should be expected because of imperfections in the printing and tape manufacturing process. If you take a ruler and measure a one foot distance (30.5 cm) anywhere along the tape, it should measure this distance precisely. If it does not, then you can devise a “correction” factor to account for the discrepancy as would be done with skinfolds. In our experience, plastic tape measures “stretch” with continual use in the middle region of the tape. We recommend a calibration check on a monthly basis.To calibrate the tape, pull the tape all the way from the plastic holder and lay it on a flat surface. Measure each 10 cm distance with a centimeter ruler from 10 to 150 cm on the tape. The 14  interval distances should each measure 10 cm. If one distance measures 9 cm, then add 1 cm to that distance when you take a client’s measurement. For example, you measure 9 cm in the range of 50 to 60 cm on the tape. If you measure a client’s thigh girth as 55.5 cm, add 1 cm to that measurement to “correct” for the 1 cm discrepancy in the 50 to 60 cm range. Thus, your client would have a 55.5 cm plus 1 cm = 56.5 cm thigh girth. If the discrepancy anywhere along the tape exceeded 1 cm, making a true 10 cm reading now measure 11.5 cm, then subtract 1.5 cm from the client’s measurement that falls within the calibration range. Correcting a tape measure score for any discrepancy when you calibrate the tape will ensure a more accurate girth score. Obtaining reliable and valid girth measurements becomes increasingly important when comparing “before” and “after” scores, not only for skinfolds but girths as well.

If body fat percent exceeds the recommend guidelines (men = 20%, women = 30%), can the person still be in good physical condition without a need to reduce?

Yes, having excess body fat does not exclude individuals embodying a healthy lifestyle and achieving a high level of fitness. Excess fat accumulation does not necessarily trigger health-related problems. However, it has been our experience that carrying around excess fat influences “normal” function in many subtle and not so subtle ways that affect mainly the psychological domain.  Glenn Gaesser’s Big Fat Lies: The Truth about Your Weight and Your Health. Gurze Books. 2002 (www.gurze.net), provides interesting insights about the role of “fatness” in overall health and fitness.