1. Body Composition Techniques 21

2. Doubly Indirect Methods for the Estimation of % Body Fat1

3. General Research Approach for Doubly Indirect Methodologies
Selected subject sample based upon required criteria. Equations produced will be highly sample specific.
Determine body density or % fat of each subject using an accepted indirect methodology; often underwater weighing
Measure subjects with new predictor measure
Produce regression equations to best predict density or % fat from new predictor measure
Equations often also include height, weight and activity level and are age and sex specific

4. Regression Equations to Predict % Body Fat
% Body Fat from Indirect Method = m(New Predictor Variable Measures) + c
Regression Analysis produces: m = slope, c= intercept
Correlation Coefficient (r)
Standard Error of Estimate (SEE in units of Y)
% Body Fat from Indirect Method
New Predictor Variable Measures

5. Doubly Indirect Methods for Estimating % Body Fat
There are no constants that can be applied to these predictor variables that will give a prediction of % Fat. They are all doubly indirect methodologies
Skinfold (Anthropometric) predictions
Ultrasound
Radiography
Bioelectrical Impedance Analysis (BIA)
Near-infrared Spectrophotometry (NIR)
DEXA (Dual Energy X-Ray Absorptiometry)

6. Anthropometric (skinfolds) prediction of % Fat
Adipose Tissue
Adipose Tissue not Fat
Equations predict % Fat (Lipid)
Over 100 equations available for the prediction of percentage body fat or body density
All are sample specific
Specific for age, gender, activity level, nutrition etc.

7. Assumptions inherent in prediction of % Fat from Skinfolds
Based upon densitometry
“Which is better UW Weighing or Skinfold predictions?”
%fat from skinfolds is predicted using equations developed from UW Weighing of subjects.
UW Weighing: S.E.E. = 2.77% Fat Skinfolds: S.E.E. = 3.7% Fat

8. Assumptions inherent in prediction of % Fat from Skinfolds
Constant Skinfold Patterning
Constant Skinfold Compressibility
Constant Tissue Densities
Constant Ratio of external/internal adipose tissue
Constant Fat (lipid) content of adipose tissue

9. YUHASZ Male: % Fat = 0.1051(Sum 6 SF) + 2.585
Female: % Fat = (Sum 6 SF)
Canadian University Students
Can never give a negative answer.
What if weight alone changes or is different?

10. Durnin & Womersley Density = a (log10Sum 4 SF) + c
Overpredicts by 3 - 5% Fat
British (left side)
Age and gender specific equations
Upper body sites
Electronic Skinfold Caliper

11. Ultrasound High Frequency Sound (6 MHz)
Some sound reflected at tissue interfaces
Time taken for return of sound used to estimate distance based upon assumed speed of sound in that tissue

12. % Fat prediction from Ultrasound
Regression equations predicting densitometrically determined % Fat
S.E.E.’s comparable to skinfold predictions
Beware of “predict anything from anything” once it is in a computer

13. RADIOGRAPHY Measurements from radiographs
uncompressed tissue thicknesses
Regression equations predicting densitometrically determined % Fat

14. BIOELECTRICAL IMPEDANCE ANALYSIS (BIA)
BIA measured by passing a microcurrent through the body
% Fat predicted from sex, age, height, weight & activity level + BIA
Influenced by hydration level
Claims that you can guess % fat more accurately

15. Bioelectrical Impedance Analysis
BIA measures impedance by body tissues to the flow of a small (<1mA) alternating electrical current (50kHz)
Impedance is a function of:
electrical resistance of tissue
electrical capacitance (storage) of tissue (reactance)

16. BIA: basic theory
The body can be considered to be a series of cylinders.
Resistance is proportional to the length of the cylinder
Resistance is inversely proportional to the cross-sectional area

17. Typical BIA Equations Males Females Where % BF = 100 x (BW-FFM)/BW
FFM = H2/R W R
Females
FFM = H2/R W R
Where
FFM = fat free mass (kg)
H = height (cm)
W = body weight (kg)
R – resistance (ohms)
% BF = 100 x (BW-FFM)/BW

18. BIA: Advantages and Limitations
costs ($500-$2000)
portable
non-invasive
fast
Limitations
accuracy and precision
no better, usually worse than hydrodensitometry

19. Major types of BIA analyzers

21. Client Friendly

22. Site Specific?

23. BIA Protocol Very sensitive to changes in body water
normal hydration
caffeine, dehydration, exercise, edema, fed/fasted
Sensitive to body temperature
Avoid exercise
Sensitive to placement of electrodes
conductor length vs. height

24. Near Infra-Red Spectrophotometry (NIR) FUTREX
Near Infra-Red light emitted from probe
Reflected light monitored
Changes due to differing optical densities
Influenced by hydration
Relative Fat/Water Index may be useful

25. Dual-Energy X-ray Absorptiometry

26. DEXA, DXA Dual Energy X-ray Absorptiometry
Two different energy level X-rays
Lean, fat, and bone mass each reduce (attenuate) the X-ray signal in unique ways
Whole body
Regional
Osteoporosis

27. X-Ray Measurement System
Dual energy attenuation values are measured for each point in the image
Calibration standards (acrylic, aluminum, delrin) are measured
The fat and lean mass of each point in the image is calculated by direct comparison to the standards

29. BMI = 12.6 %Fat = 3.2% BMI = 18.1 %Fat = 23.1% BMI = 23.7 %Fat = 48.1%
These are images from anorexic, normal, and obese subjects. The brightness of the image is proportional to material density. The bone is the most dense, followed by muscle, and then fat. The subcutaneous fat around the hips can be seen on the normal and obese subject.
BMI = 12.6
%Fat = 3.2%
BMI = 18.1
%Fat = 23.1%
BMI = 23.7
%Fat = 48.1%

30. What DEXA Measures Fat and fat-free mass (based upon the standards)
Bone Mineral Mass
Regional results for the above

31. DEXA Cannot Measure... Protein Mass 3-D Fat Distribution
Hydration Status
Tissue inside bone (brain, marrow, blood)

32. Next generation of Body Composition Models
Two compartment plus
Water
Bone mineral
Protein
3 or 4 compartment models now regarded as the reference standard rather than underwater weighing