Many people rely on the scale in determining whether or not they are considered obese. However, your numerical weight does not differentiate between muscle mass and fat mass. In fact, a scale can incorrectly classify athletes and bodybuilders as obese because of their large amounts of muscle mass. Evaluating body composition is a better method to look at what percentage of a person's body mass is fat. Skin-fold measurements are one tool that can be used to predict body fat.
Advantages
Skin-fold measurements are perhaps the most widely used method for predicting body fat. They work on the assumption that 1/3 of the body's fat lies just beneath the surface of the skin. They are popular because there is little cost involved. The only equipment needed is a quality skin-fold caliper and a trained technician. The American Council on Exercise estimates that a quality caliper can be purchased for $300 and can be used repeatedly with hundreds of clients. Skin-folds also remain popular because the measurements can be taken rather quickly and easily, with little discomfort to the client. The American College of Sports Medicine, ACSM, also says that skin-fold measurements provide an accurate estimate of body fat when compared to underwater weighing, which is the gold standard in predicting body fat.
Technique
ACSM recommends taking all skin-fold measurements on the right side of the body while the subject is standing. The calipers should be allowed to rest on the skin surface, approximately 1cm from the thumb and finger. The calipers should be held perpendicular to the skin-fold. While you are reading the caliper, hold the pinch of the skin and wait one to two seconds before reading the measurement. Rotate through all of the sites, and then repeat them to verify your readings. If your measurements are within 1 to 2mm, average the two and move on. If the measurements vary by more than 2mm, take a third measurement and average the two closest.
Sites
The ACSM lists nine sites that you could possibly use for skin-fold measurements. The sites that are evaluated with a vertical fold are the abdominals, triceps, biceps, calf, midaxillary and thigh. The subscapular, suprailliac and thigh sites are all assessed on a diagonal fold.
Formulas
Typically, you will not assess all nine sites when assessing body composition. There are several formulas that you can chose, and which formula you select then determines the number and locations of sites to measure. The ACSM recommends the three- and seven-site formulas that have been developed for both males and females. The seven-site formulas for both men and women use the same skin-fold sites. The sites are the chest, midaxillary, triceps, subscapular, abdomen, suprailliac and thigh. Males can use chest, abdomen and thigh or chest triceps and subscapular measurements for two different three-site formulas. Females can use either the triceps, suprailliac and thigh or the triceps, suprailliac and abdominals in one of their three-site formulas.
References
- "ACSM's Guidelines for Exercise Testing and Prescription" Eighth Edition; Lippincott, Williams & Wilkins; 2010
- Exercise Prescription: Skinfold Procedures
- ACE Fitness: Percent Body Fat Calculator
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