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Skin-fold measurements

The development of skin-fold (anthropometric) measurements came as the result of investigations for simpler and less expensive methods of estimating body composition. The skin-fold measurement test is one common method of determining body composition and body fat percentage – this method is the most widely used body composition testing method for assessing percent body fat.

This test estimates the percentage of body fat by measuring skin-fold thickness at specific locations on the body. The thickness of these folds is a measure of the fat under the skin, also called “subcutaneous adipose tissue”. Skin-fold thickness results rely on formulas that convert these numbers into an estimate of the percentage of body fat according to age and gender.
In most cases the skin-fold measurements are taken at specific sites on the right side of the body. The specific tester (called caliper) pinches the skin at the location site and pulls the fold of skin away from the underlying muscle so only the skin and fat tissue is being held.

Special skin-fold calipers are used to measure the skin-fold thickness in millimeters. Skin-fold caliper is designed specifically for simple accurate measurement of subcutaneous tissue. Usually two measurements are recorded and averaged.

The measurement sites vary depending upon the specific skin-fold testing protocol being used, but typically include the following seven locations on the body:

Skin-Fold during obesity

1. Triceps – The back of the upper arm
2. Pectoral – The mid-chest, just forward of the armpit
3. Subscapula – Beneath the edge of the shoulder blade
4. Midaxilla – Midline of the side of the torso
5. Abdomen – Next to the belly button
6. Suprailiac – Just above the iliac crest of the hip bone
7. Quadriceps – Middle of the upper thigh

ACCURACY of the skin-fold measurements

To take a skin-fold measurement, first determine the correct measurement site. Grab the skin with the thumb and forefinger about 0.5 inches from the measurement site following the natural fold of the skin. Lift the skin up from the muscle, apply the calipers and wait for 4 seconds before reading the calipers. Fat is compressible, so reading the scale before or after the 4-sec delay may affect the results.

If each test is performed correctly according to the recommended guidelines, there is a +/- 3% error.

Skin-fold measurements – advantages

Skin-Fold Measurements

  • Easy to use once skill has been mastered,
  • Does not require much time,
  • Noninvasive method,
  • Inexpensive way of estimating percent body fat.

Skin-fold measurements – disadvantages

  • Technical sources of error,
  • Mostly concerned with subcutaneous fat (under the skin),
  • May not be an ideal measurement for those who are obese and very lean.

Skin-fold measurements & Body Density Estimation

There are two calculation steps for determining percent fat; determining body density and then using body density to estimate percent fat. All the skin-fold equations estimate body density from the measurements which is then used to estimate percent fat. Two generalized equations that have withstood the test of numerous cross-validation studies are ones published by Jackson and Pollock (1978) for men and Jackson, Pollock, and Ward (1980) for women. Each study developed numerous equations based on different skin-fold measurements, although they all were similar in prediction error. Listed below are single equations from each study based on the sum of three skin-fold measurements. Standard errors of their formulae ranged from 3.6% to 3.8%. The potential errors are increased if these equations are used on the young or old, very lean and muscular or obese. Other, population specific equations are available and more suitable for these groups.

                                      FEMALES  

Body Density = 1.0994921 – 0.0009929*sum + 0.0000023*sum2 – 0.0001392*age

(triceps, suprailiac, thigh skin-fold measurements)

                                      MALES

Body Density = 1.1093800 – 0.0008267*sum + 0.0000016*sum2 – 0.0002574*age

(chest, abdominal, thigh skin-fold measurements)

Skin-fold measurements & Fat Percent Estimations

The two most commonly used equations for estimating percent fat from body density are the Siri (1961) and Brozek (1963) formulae. A limitation to these formulae is that they assume the density of fat-free mass to remain a constant across the population when in fact is varies. Thus, the actual percent fat tends to be slightly higher than the measured percent fat in the lean, muscular individual and the opposite effect in obese individuals.

Siri Percent Fat = [(495 / Body Density) -450] * 100
Brozek   Percent Fat = [(4.570 / Body Density) – 4.142] * 100

Obesity levels

 

 


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