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. DEXA is now considered the Gold Standard in Total Body Fat Analysis.
When having the scan done, you just lie 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:
Radiation exposure is low
DEXA is quick
There is no special preparation on the part of the participant
Disadvantages:
DEXA is costly
Few centres have it
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 lean 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 3%-4% 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:
Until DEXA came along, this was considered the Gold Standard. It still is considered the Gold Standard in sports labs without DEXA equipment.
Repeat measures usually prove consistent, and can be used to chart progress
Disadvantages:
This method usually requires a lot of equipment and space
Testing is time consuming and involved
Requires in-depth knowledge to administer the tests and compute the calculations
Being submerged under water may be difficult and produce anxiety for some people
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:
- chest
- triceps
- subscapular
- axilla
- suprailiac
- abdomen
- thigh
3 site skinfold (Men):
- chest
- abdomen
- thigh
3 Site Skinfold (Women)
- tricep
- suprailiac
- thigh
How accurate is it?
The measurement charts were designed with a Caucasian Population. Unless you have an Asian (by Chinese, Indian, categories) , these charts are misleading. The skin fold test is also not used for obese or elderly persons with a pot belly. I've not seen a skin fold measurement chart yet designed for Singapore Chinese, or Singapore Indian population.
Advantages:
Easy to use once skill has been mastered
Does not require much time
Noninvasive method
Inexpensive way of estimating percent body fat
Disadvantages:
Technical sources of error
Mostly concerned with subcutaneous fat (under the skin)
May not be an ideal measurement for those who are obese and very lean
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 5%-10%. However, accuracy is dependant upon several variables. It is recommended the following guidelines be followed:
- Abstain from eating and drinking 4 hours prior to the test
- Avoid exercising 12 hours prior to the test
- Void (urinate) completely prior to testing
- Do not drink alcohol 48 hours prior to the test
- Avoid taking diuretics prior to testing unless instructed by your physician
Advantages:
Requires little or no technical knowledge of the operator or the client
Testing itself takes less than a minute
The unit can be easily transported from place to place
Requires only an electrical outlet and the machine itself Disadvantages:
This method has a higher standard error range than most people desire
Tends to consistently overestimate lean people and underestimate obese people
The accuracy BIA does have is very dependant on multiple variables which may be hard to control for some people
Near Infrared Interactance (NIR)
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.
How Accurate is it?
This method of assessing body fat is not the most accurate. It was found that skinfolds more accurately predicted body fat than NIR when underwater weighing was used as the criterion measure.
