Beyond Pinching An Inch

How to Measure and Interpret Your Body Composition

Techniques for Measuring Body Composition

We can only estimate body fat, and even the best methods have errors in the range of 3%. In other words, if you’re told you have 12% body fat, you could have between 9% and 15%. The following methods are among the most popular.

Hydrostatic (underwater) weighing. This method involves being weighed underwater after expelling all the air from the lungs. The difference between your land weight and water weight is used to estimate body density, from which percent body fat is extrapolated. Considered the most accurate method, underwater weighing can be expensive, time-consuming (repeated dunkings are required) and uncomfortable, as you must remain underwater for up to 10 seconds after expelling your breath. Also, the formulas used may not be accurate for some athletes, such as older and non-Caucasian runners. Sports medicine centers, hospital-based wellness programs and universities with an exercise science program typically offer hydrostatic weighing.

Air displacement (Bod Pod). A new technology, this method requires that you sit in an enclosed capsule for about a minute while computer sensors measure the amount of air displaced by your body. Research findings indicate that the method is reliable and valid in healthy adults; however, additional studies are needed on competitive athletes. Although fast and easy, the method can be expensive and is not yet widely available. Check universities and athletic facilities serving professional and collegiate athletes.

Skinfold calipers. A tester uses calipers to pinch and measure the fat located right under the skin on several parts of the body, usually the abdomen, thigh, hip, and the back of the arm and shoulder. Simple, painless and inexpensive, this technique can provide accurate and reliable readings (if the measurement taker is skilled), although it tends to underestimate body fat in lean athletes. Serial measurements can monitor changes in body composition over time.

Bioelectrical impedance analysis (BIA). In this technique, a mild electrical current is passed through the body. Because muscles contain most of the body’s water and electrolytes, they conduct the current more quickly than fat stores; thus the slower the signal the more fat you have. Quick and painless, BIA is offered routinely at fitness clubs and health fairs. Be aware that it tends to overestimate body fat percentage in lean individuals, and that fluid changes, such as being dehydrated, can skew the measurements. For best results, avoid alcohol and caffeine for 24 hours, don’t exercise for 12 hours and don’t eat or drink for four hours prior to the test.

Interpreting Your Results

Chances are, you’re within a healthy range and don’t need to make any changes. As with weight, aim to be within a healthy range rather than obsessing over the exact number and fretting about slight variations over time. Susan Fox, director of the Human Performance Lab at Oregon State University, suggests that athletes monitor changes in body fat over a season, such as before and after a specific phase of training. She also notes that to make a valid comparison, you must use the same method each time.

If you fall significantly outside the healthy range, consult a registered dietician or sports medicine physician to help you achieve a more appropriate level.