1. AIR-DISPLACEMENTPLETHYSMOGRAPHY (i.e. Bod Pod)

2. Densitometry Plethysmography Plethysmography  Known as the “Bod Pod”  Based on volume differences between fat mass and fat-free mass  Leaner individuals have less volume per mass than fatter individuals  Technology allows volume (air displacement) to be measured by pressure changes in a closed chamber

3. 220 kg vs. 191cm

4. AIR-DISPLACEMENT PLETHYSMOGRAPHY “Plethys” = old Greek word for pressure “Plethys” = old Greek word for pressure ADP determines body volume by measuring the the volume of air-displaced from a chamber by an object ADP determines body volume by measuring the the volume of air-displaced from a chamber by an object Archimedes’ Principle states, “An object immersed in water is buoyed up by a force equal to the weight of the water displaced.” Archimedes’ Principle states, “An object immersed in water is buoyed up by a force equal to the weight of the water displaced.”

5. Introduction to Physical Principles Calculation of volume of air in empty chamber Calculation of volume of air in empty chamber Calculation of volume of air in chamber with subject present Calculation of volume of air in chamber with subject present Volume empty – Volume subject Volume empty – Volume subject = Subject body volume

6. Introduction to Bod Pod Physical Principles BV is corrected for thoracic gas volume (TGV) BV is corrected for thoracic gas volume (TGV) Body surface area estimated from height and weight Body surface area estimated from height and weight Boyles Law: P 1 V 1 = P 2 V 2 Boyles Law: P 1 V 1 = P 2 V 2 P test V test = P ref V ref P test V test = P ref V ref V ref is known, if measure P ref and P test then V test can be calculated V ref is known, if measure P ref and P test then V test can be calculated

8. ADP Technique Faster and easier than UWW Faster and easier than UWW Follow pretest guidelines Follow pretest guidelines Minimal, tight clothing and swim cap are essential for accuracy Minimal, tight clothing and swim cap are essential for accuracy Closely follow calibration procedures and computer prompts during testing Closely follow calibration procedures and computer prompts during testing