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

7 site skinfold:

• chest
• triceps
• subscapular
• axilla
• suprailiac
• abdomen
• thigh

3 site skinfold (Men):

• chest
• abdomen
• thigh

3 Site Skinfold (Women)

• tricep
• suprailiac
• thigh

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:

• Lange Skinfold Caliper: This type of caliper is widely used in schools, colleges, and fitness centers. It is very popular among physical educators, coaches, and health and fitness professionals. The price range is $ 179.00 – $220.00.
• Harpenden Skinfold Caliper: the standard caliper used in research. The majority of data involving body composition assessments dealing with the relationship of skinfold thickness to percent body fat in use today are based on studies using this caliper. It’s accuracy is within ± 0.2 mm and can be read to the nearest 0.1 mm. Harpenden Skinfold Caliper is popular among Exercise Scientists and or Health Science Researchers. The price range is $275.00 – $400.00.

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

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

• School
• College
• YMCA
• Hospital Based Wellness Program
• Recreational Program
• Commercial Fitness Club
• Community Fitness Club
• Sport/Exercise Physiology Laboratory

Underwater 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:

• This method is currently considered the "gold standard" in percent body fat measurement
• Repeat measures usually prove consistent, and can be used to chart progress

• 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

• Usually hydrostatic weighing will cost anywhere from $10-$75 due to the involved nature of the test.

• Available at research institutions and colleges or universities
• Discounted pricing is usually available for students.

Bioelectrical Impedence

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:

• Abstain from eating and drinking within 4 hours of the test
• Avoid exercising within 12 hours of the test
• Void (urinate) completely prior to testing
• Do not drink alcohol within 48 hours of 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

• 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

• BIA machines can be purchased for home use for anywhere between $100-$400.
• To be measured on a machine at a school or club, prices range from free to $30 per use.

• BIA is popular in health and fitness clubs due to its ease of operation.
• They may also be found at health fairs, schools or universities.

Bod Pod (Air Displacement)

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

• Hydration status and increases in muscle temperature can adversely affect calculation results
• Also, it is imperative to breath normal, remain still, and keep hands in lap while being assessed by the Bod Pod (any slight movement or change in breathing pattern may affect results)

• Spandex shorts (Imperative that tight fitting shorts are worn)
• Swim cap

• Does not require getting wet
• Not difficult to operate
• Measurement time is short
• Well suited for special populations (children, obese, elderly, and disabled persons)

• Very expensive ($30,000 - $40,000)
• Only a few facilities have the Bod Pod

• Available at research laboratories
• Available at athletic facilities (Pro and College)

• $40 - $65 per visit

Dual Energy X-Ray Absorptiometry (DEXA)

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
• One does not have to wear a bathing suit or skimpy clothing
• There is no special preparation on the part of the participant

• DEXA is costly

• DEXA may cost as much as $300

• It can be done at universities and research facilities
• It may be free for those participating in a research study

Near Infrared Interactance (NIR) Futrex 5000

How Accurate is it?

• This method of assessing body fat is not the most accurate. In a study by *Mclean et al (1992), it was found that skinfolds more accurately predicted body fat than NIR when underwater weighing was used as the criterion measure. In their study, Futrex 5000 underestimated body fat by more than 4% in subjects greater than 30% fat and overestimated body fat by 4% in subjects less than 8% fat. * Medicine and Exercise in Sports and Exercise.  Validity of Futrex-5000 for Body Composition. Vol. 2   No.2 pg. 253-257, 1992

• Safe
• Non-invasive
• Fast
• Convenient.

Disadvantages:

• Not one of the most accurate techniques used to assess body fat composition.

Cost:

• Fairly inexpensive. It may cost anywhere from twenty to forty dollars.

• Health clubs
• Weight loss centers
• Medical practices offering weight loss programs

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