Getting on the scale may be useful in helping you gauge whether you've lost weight, gained a few pounds, or are holding steady, but it won't give you insight into your body composition -- the relative proportion of fatty tissues and lean mass in your body. Body composition can be a predictor of your overall health. The amount and distribution of your body fat may correlate with your risk of developing hypertension, diabetes and other obesity-related illnesses. The body fat pinch test -- commonly known as the skinfold test -- is one of the simplest techniques for estimating body fat and evaluating body composition. It's most accurate when performed by an experienced professional.
Locate the Sites for the Pinch Test
The skinfold test is based on the premise that roughly half of total body fat is subcutaneous, or lies just below the skin. The test measures the thickness of skinfolds at specific sites on the right side of the body. These sites are somewhat different for men and women because gender influences where fat is stored. The three main skinfold sites for women include the triceps, taken vertically along the back of the arm midway between the shoulder and the elbow; the thigh, taken vertically midway between the hip and knee along the front of the leg; and the suprailium, taken diagonally just above the top of the hip bone. The three main skinfold sites for men are the chest, taken diagonally midway between the top of the underarm and the nipple; the thigh, taken vertically midway between the hip and knee along the front of the leg; and the abdomen, taken vertically an inch to the right of the navel. Use a measuring tape to find each site, and mark them precisely with an eyebrow pencil or a washable marker.
Take the Measurements
To take a measurement at any of the standardized sites, you need specifically designed skinfold calipers. Although skinfold calipers range in price from less than 10 dollars to several hundred dollars, the cost of your equipment doesn't necessarily indicate its accuracy. Holding the calipers in your right hand, firmly grasp the marked skinfold with your left thumb and index finger, and lift it slightly so that as you pinch the fold together, you're only holding two layers – skin and fat. Place the pads of the open calipers perpendicular to the skinfold, just above or below your fingers, and read the measurement to the nearest half of a millimeter. Open the calipers before removing them from the skinfold. The person you're measuring should be standing and relaxed for best results.
Don't take measurements on someone who has just exercised – the American Council on Exercise points out that exercise can increase the amount of fluid in the skin, which can inflate results.
Repeat the Measurements
Just as keeping all skinfold measurements to the right side of the body promotes reliability, taking a minimum of two measurements at each site helps ensure accuracy. It's important to not repeat any single measurement too soon; fat tissue needs at least 15 seconds to redistribute to its normal thickness before it can be re-measured accurately. Taking measurements in ascending or descending order on the body, and then measuring a second time in the same order, can help you avoid the problem of retesting too soon. If a second measurement varies from the first by more than 1 millimeter, wait and measure the site a third time. The American Council on Exercise recommends continued testing until you get two measurements that are less than 1 millimeter apart.
Calculate the Percentage of Body Fat
Many formulas have been devised to estimate body fat percentages from skinfold tests. Some formulas are based on specific populations, such as female athletes, for example, and they won't give an accurate result to someone from the general population. Formulas based on the sum of each skinfold measurement, such as the Jackson-Pollock formula or the Durnin-Womersley formula, are generally more accurate for the average person. Plug the data on the person you tested into the appropriate formula, do the calculations, and then look up the results on a chart to get the resulting body fat percentage.
While the standard error for the skinfold test is 3.5 percent, accuracy depends largely on finding the sites accurately, folding only the appropriate tissues, using the calipers correctly and choosing the right formula. Having your own measurements taken and calculated by an experienced professional who is well-versed in the proper technique, such as a registered dietitian or a personal trainer, will give you a more accurate estimation of your body fat percentage.
- Archives of Diseases in Childhood: Measuring Body Composition
- Human Kinetics: Choose the Correct Method for Body Composition Assessment
- ACE Fit: Percent Body Fat Calculator -- Skinfold Method
- American College of Sports Medicine: Measuring and Evaluating Body Composition
- PT Direct: Taking Skinfold Measurements
- National Academy of Sports Medicine: Assessing Change -- Beyond the Number on the Scale
- UMass Lowell: Determination of Body Composition