Bod Pod (Air Displacement)
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Definition
An air displacement plethysmography method that measures a person’s total body density (Db) by using the ratio of body mass to body volume (BV).Along with water displacement, air displacement is a form of Densitometry
How it Works
Relies on the relationship between pressure and volume, and allows for the derivation of an unknown volume by directly measuring pressure.
Steps For Testing
- Get an accurate body weight outside of water
- Have person sit on scale over the water and then be submerged
- Measure body weight while being submerged under water
- Simultaneously measure the Residual Lung Volume (RV) as the person blows out their air
- Apply the results to previously mentioned formulas.
Formulas Used
Once the total body density is determined (Db), it’s then applied to one of the following two formulas resulting in a Body Fat Percentage (BF %).
- Siri formula is: BF% = [(4.95/Db) - 4.50] x 100
- Brozek formula is: BF% = [(4.57/Db) - 4.142] x 100
Accuracy
Research shows that the accuracy is within 1-2%.
Disadvantages
- Gender, age, physical activity level, and ethnicity can cause an error in the calculations
- Hair and clothing can effect the results
- Expensive equipment
- Not very accessible to the average person
Advantages
- Small margin of error
- More accurate measurement of BF%
- Less complex testing - only need to sit in a chamber and breathe
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