Lab 2 Body Composition Assessment from Underwater Weighing

Underwater Weighing Indirect method for determining –Body density –Amount of fat component –Amount of fat-free component

Archimedes’ Principle An object immersed in a fluid loses an amount of weight equivalent to the weight of the fluid displaced. Difference between “dry” weight and underwater weight reflects the volume of water displaced, and this is equal to the individual’s body volume. Underwater weighing can be used to determine body volume.

Body Density Consists of –Amount of lower-density (fat component) tissues –Amount of higher-density (fat-free component) tissues Can be determined by –Dividing “dry” body weight by body volume

Obesity An excessive amount of body fat 30% of body weight consisting of fat

Desirable Fat Levels Males –10 to 15% FAT Females –15 to 20% FAT

Lowest Healthy Fat Levels Adult males –5% FAT Adult females –12% FAT

Overweightness An excessive body weight in comparison to what is the standard body weight based on one’s height, age, gender, and frame size Overweightness may not indicate obesity and vice versa.

Three measures used to determine body composition 1.Residual lung volume (RV) 2.Body weight (BW) 3.Underwater weight (UWW)

Calculation of Residual Lung Volume 1.Determine the BTPS (body temperature pressure saturated) correction factor from Table 2.1 based on the recorded air temperature in the spirometer. For instance, if air is 28° C, BTPS = Select the highest of the three VC values and correct it for BTPS: VCBTPS = (VC x BTPS) Example: VC BTPS = (4.35 L x 1.057) = L 3. Estimate RV based on: RV = (VC BTPS x 0.24) for males Or RV = (VC BTPS x 0.28) for females Example: (assume previous VC data was for a female) RV = (4.598 x 0.28) = L

Calculation of Body Composition Slide 1 1.Convert dry body weight (DBW) from pounds to kilograms by dividing by Example: (127.5 lbs. / ) = kg 2. Determine underwater weight (UWW) based on the average of the three “heaviest” trials. 3. Correct for the weight of the apparatus to derive the true underwater weight (TUWW) of the subject. The weight of the apparatus is called tare weight. Example: If the average UWW of the best trials is kg and the tare weighs 4.91 kg, TUWW = (7.833 – 4.91) = kg

Calculation of Body Composition Slide 2 4. Determine water density from water temperature using Table 2.2. Example: If H 2 0 temp = 33° C, then DH 2 0 = Calculate body volume (BV) from dry body weight (DBW), TUWW, water density (DH 2 O), and RV, as well as a constant of 0.1 L, which is an estimate of the air in the digestive tract based on: BV = ((((DBW – TUWW) / DH 2 0) – RV) – 0.1) Example: BV = (((( – 2.923) / ) – 1.287) – 0.1) = Calculate body density (BD) from BW and BV based on: DB = (DBW / BV) Example: DB = / ) = kgּL -1

Calculation of Body Composition Slide 3 7.Convert body density to % FAT using the following standard formula: % FAT = (((4.57 / DB) – 4.142) x 100) Example: % FAT = (((4.57 / ) – 4.142) x 100) = 11.0% 8.Calculate fat weight (FW) and fat-free weight (FFW) using the following calculations: FW = (DBW x (% FAT / 100)) Example: FW = ( x (11.0 / 100)) = kg FFW = (DBW – FW) Example: FFW = ( – 6.362) = kg

Setting Body Weight Goal 1.Select a target value for the % FAT level you want to achieve. Example: Currently at 11% FAT, and the goal is 10% FAT. 2.Using the target value for % Fat and the current value for FFW, calculate the BW goal as follows: BW goal = (FFW / (1 – (TARGET % FAT / 100)) Example: BW goal = ( / (1 – (10 / 100 )) = kg Thus at 10% FAT this subject would weigh kg and would need to lose kg of body weight to reach this goal (assuming all of the weight lost was from FW).