Body Composition Explained

BODPOD Explained

Other Body Composition Techniques

There are many options when it comes to measuring Body composition. Measurement techniques can vary greatly, however many methods can become very difficult to perform, are relatively invasive, and many field methods used are highly inaccurate.

Bodyology Exercise Science Studio shares the views of Life Measurement Incorporated, that the need for technology such as the BOD POD was evident due to the disadvantages of other methods.

Laboratory or Research Methods include the BOD POD, Hydrostatic Weighing and DXA Scans. These tests offer the most accurate analysis, but the BOD POD offers the same accuracy with greater ease and safety. Other quick methods are often referred to as Field Tests as they are methods commonly used in settings outside of the laboratory and are designed to be quicker and cheaper than laboratory techniques. This compromise on quality and price results in a reduction in accuracy, as would be expected.

Hydrostatic (Underwater) Weighing

The previous gold standard method, this technique determines body fat from body density (the ratio of body weight to body volume). ie. Density  = Mass/Volume. In this sense the theoretical nature of hydrostatic weighing and Air Displacement Technology are the same. In this procedure the subject sits strapped in a chair that is submerged into a water tank and weighed. While submerged, the subject must expel all the air from their lungs and hold their breath for 10-15 seconds until the scale can be read. This process is repeated up to 10 times to ensure accuracy. Such facilities are very rare in Australia, yet may be found at Universities and research facilities. Testing can take between 30-60 minutes and requires multiple testers.

Hydrostatic Weighing is an established reference method for measuring body density. (Laboratory Method) and is known to be very accurate when compliance issues can be followed properly.  However, testing can be lengthy, arduous, and very difficult to perform correctly. Technicians must be highly skilled in order to obtain accurate results.

Some populations are impossible to test, including the extremely obese, disabled, elderly, infants and small children, and those with an aversion to water. Water temperature needs to remain constant and the tank should be drained after each measurement, since dirty water can skew results. A wide range of equipment, protocols, calibration, and methods for determining residual Thoracic Lung Volume (TGV) can contribute to measurement errors.
There are obvious hygiene issues, and due to an array of ongoing maintenance issues and multiple technicians, tests can also be expensive.

Dual Energy X-Ray Absorptiometry (DXA)

This technique was initially developed to measure bone mineral density, not body composition. During testing a subject lies on a table and the body is slowly scanned. Computer software then reconstructs an image of the underlying tissue to determine total fat and lean mass. Testing time, including preparation can be around 10 minutes.
DXA scans provide very accurate results and testing is a relatively comfortable procedure. However, the use of x-ray technology is invasive and usually requires testing to be undertaken at medical facilities, with specialist technicians, not Exercise Scientists. Scanning beds cannot accommodate extremely large people and different DXA equipment often produces different results. A wide range of equipment, protocols, calibration, and methods for determining Residual Thoracic Lung Volume (TGV) can contribute to significant measurement errors. Due to the nature of the scans and technicians, DXA scans are usually very expensive also.

Bioelectric Impedance

Considered a field method, this technique is based on the concept that the lean tissue of the body is more conductive than fat tissue due to its higher water content. Testing involves placement of electrodes on the skin, while a low dose electrical current is passed through the body. The resistance to this current is determined and converted to percent body fat. The same concepts are used in commercial body-fat scales. Tests can be as quick as 30 seconds on scales, however more advanced devices requiring setup may take up to 5 minutes.

Skinfold Callipers

Considered a field method, this technique measures subcutaneous fat (fat just under the surface of the skin) at several sites on the body by pinching the skin with callipers. The assumption is that subcutaneous fat is proportional to the subject’s total body fat. Testing can take from a few minutes up to 20 minutes depending on the tester and number of sites used. The test is generally inexpensive and easily performed in the field; however well-trained individuals may charge higher rates for measurements.
As only subcutaneous fat is being measured, the greater picture of total body fat is not necessarily considered. Large errors can occur between testers and from test to test, depending on the accuracy of the tester and the precise locations of measurement sites. Many different equations can be used, meaning that the same measurements applied to different equations can result in different body fat readings. This method is not valid for obese populations, and is generally an unpleasant test, due to repeated readings at sites for accuracy.

Body Mass Index (BMI)

This is a mathematical calculation based on a subject’s height and weight, which is used to make an assumption of the subject’s body fat. This test can take less than 2 minutes and is very inexpensive and easy to perform. However, there is no direct measurement of body fat or lean muscle, or even a distinction made between the two. Therefore muscular clients can be misclassified as obese, which is particularly troublesome in sporting and athletic populations. BMI does not take into account age, gender, and ethnicity when determining results.