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Body Composition

Body Composition Methods:

Skinfold Measurements
Underwater Weighing
Bioelectrical Impedence
Bod Pod (Air Displacement)
Dual Energy X-Ray Absorptiometry (DEXA)
Near Infrared Interactance (NIR) Futrex 5000

Skinfold Measurements

Description: This method is the most widely used body composition testing method for assessing percent body fat. Equipment used for this assessment includes a skinfold caliper. A Skinfold Caliper is designed specifically for simple accurate measurement of subcutaneous tissue. Either a 7 or 3 site skinfold may be assessed.

7 site skinfold:

3 site skinfold (Men):

3 Site Skinfold (Women)

How accurate is it?

If each test is performed correctly according to the recommended guidelines, there is a +/- 3% error. Validity (compared to underwater weighing): 7 site skinfold (r = .90), 3 site skinfold (r = .89).*

Commonly used calipers:

Advantages:

Disadvantages:

Where can I have my body composition assessed by skinfold calipers?


Underwater Weighing

(a.k.a. Hydrostatic Weighing)

Description: This method uses Archimedes principle which states that when a body is submerged in water, there is a buoyant counter force equal to the weight of the water which is displaced. Because bone and muscle are more dense than water, a person with a larger percentage of fat free mass will weigh more in the water and have a lower percent body fat. Conversely, fat floats. Therefore, a large amount of fat mass will make the body lighter in the water and have a higher percent body fat.

How accurate is it?

If each test is performed correctly according to the recommended guidelines, there is a +/- 1.5% error. (Note: Accuracy depends on the client’s ability to blow all the air out of their lungs both during a pre-test screening with a spirometer, and during the test itself. Since air makes the body float, inability to perform either of these maneuvers will result in miscalculation of the percent body fat.)

Advantages:

Disadvantages: Cost: Where?

Bioelectrical Impedence

Description: By standing barefoot on metal foot plates, an undetectably low voltage electric current is sent up one leg and down the other. Since fat is a very poor conductor of electricity, a lot of fat will impede the current more so than a lot of lean tissue. By measuring the resistance to the current, the machine estimates the percent body fat.

How accurate is it? BIA accuracy, if done correctly on properly operating equipment, is approximately +/- 3%. However, accuracy is dependant upon several client-based variables. It is recommended the following guidelines be followed:

Advantages:

Disadvantages: Cost: Where Can I Have it Done?

Bod Pod (Air Displacement)

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Description: One of the newest forms of body composition testing involving state of the art technology, developed by Life Measurements Instruments, Concord, CA. The use of Bod Pod correlates nicely with the concept of hydrostatic weighing (underwater weighing). Instead of using water to measure body volume, the Bod Pod uses air displacement to measure body volume.  Measurement time takes roughly 5 to 8 minutes per individual.

How accurate is it? If each test is performed correctly according to the recommended guidelines, there is a ± 3% error. According to McCrory, et al.*, the Bod pod has a validity of r = .93 using hydrostatic weighing as the criterion measure. * Medicine and Science in Sports and Exercise, 27(12): 1686-1691, 1995.

Factors that may affect accuracy of the Bod Pod

Attire required for assessment by the Bod Pod Advantages Disadvantages Where can I have my body composition assessed by the Bod Pod? How much does it cost to have my body composition assessed by the Bod Pod?

Dual Energy X-Ray Absorptiometry (DEXA)

Description:  DEXA is a fairly new technology. It is based on the three component model of body composition. DEXA uses two X-ray energies to measure body fat, muscle, and bone mineral. When having the scan done, one must lay still in the supine position on what looks like an x-ray table. It takes approximately twelve minutes for the computer software to produce an image of the tissues. The results may be viewed as whole body estimates of body fat, muscle, and bone mineral as well as regional body estimates.

How accurate is it?:  DEXA takes bone mineral content into consideration when estimating body fat and muscle, therefore it is considered to be more accurate and valid than a two component model of body composition such as underwater weighing.

Advantages:

Disadvantages:   Cost:   Where Can I Have it Done?

Near Infrared Interactance (NIR) Futrex 5000

Description: This method of assessing body fat is based on the principles of light absorbtion , reflectance, and near infrared spectroscopy. To estimate body composition , a computerized spectrophotometer that has a scan and probe are used. The probe is placed onto a selected body site such as the biceps; it emitts an infrared light which passes through both fat and muscle and is reflected back to the probe. Subject data such as height, weight, sex, age, frame size and activity level are taken into consideration. Density measurements are obtained and incorporated into the manufacturer’s prediction equations. A digital read out including percentage body fat and lean tissue are displayed. Futrex 5000 is an example of NIR.

How Accurate is it?

Advantages:

Disadvantages:

Cost:

Where Can I Have it Done?

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The Exercise and Physical Fitness Web Page is an ongoing project by graduate students in the Master of Science program in Exercise Science in the Department of Kinesiology and Health at Georgia State University. This project was created by J. Andrew Doyle, PhD, and was last modified on: March 18, 1998.