Percent body fat is a measurement that reflects how much of your body is made up of fat tissue compared to lean tissue. According to the American Council on Exercise if your body fat percentage is higher than 31 percent for women, or 24 for men, you are classified as obese. Obesity leads to premature death and an increased risk of developing a long list of chronic diseases. In order to measure your body fat percentage, various techniques, such as skin-fold measurements, have been developed.
Evaluation Methods
The only way to directly measure percent body fat is via an autopsy. Therefore, exercise professionals have developed indirect methods to estimate your body composition. The methods vary in regards to accuracy, cost and accessibility. In a research or university setting methods like underwater weighing or air displacement are common and accurate, however the equipment is expensive and not readily available to the general population. Skin-fold measurements are a good choice for the general population because they are easy to administer, cost-effective and relatively accurate. The American College of Sport Medicine notes that skin-fold measurements correlate closely with hydrostatic weighing, which is the most accurate indirect method currently available.
Technique
Skin-fold measurements are obtained using a skin-fold caliper. These calipers range in cost from $30 to $300 and can be used over and over with numerous individuals. The calipers should be used by experienced and trained technicians, usually a dietitian or exercise physiologist. Typically, you will be asked to stand with your arms hanging at your side while the measurements are taken on your right side. The technician will firmly, but not painfully, pinch areas of skin on various parts of the body. He will then place the calipers on the skin and read how thick the skin-fold is in millimeters. To ensure the accuracy of the measurements, he should repeat the measurements. If the measurements fall within 2 mm of one another they are averaged and then entered into a formula for calculation. If they fall further apart then the technician should take a third measurement and average the two closest readings.
Sites
The areas of the body that the technician measures depends on which formula he chooses to use in calculating your percent body fat. The ACSM endorses the three- and seven-site formulas as the most accurate. The formulas and sites vary depending on if you are a man or woman. The technician will use some of the nine possible sites for evaluation. The pinching of the skin is done either vertically or diagonally depending on the site. The areas in which a vertical fold is required include the abdominals, triceps, biceps, calf, mid-axillary and thigh. The diagonal fold sites are the chest, sub-scapular and supra-iliac.
Measurement Error
The concept of skin-fold assessments is based on the assumption that the amount of fat that lies just beneath the skin is proportional to the total amount of fat on the body. ACSM cites that if done correctly the estimated body fat will fall within 3.5 percent of the actual amount. However, if the technician is inexperienced or has poor technique, the results will be skewed. Additionally, skin-folds are difficult to obtain on extremely obese individuals as well as those that are very lean, therefore a different method of evaluation may be used. And finally, the calipers used should be of a high quality and calibrated regularly.
References
- American Council on Exercise Fitness: Percent Body Fat Calculators
- "ACSM's Guidelines for Exercise Testing and Prescription" Eighth edition; Lippincott, Williams & Wilkins; 2010.
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