#### Title

ESTIMATED VS. ACTUAL RESIDUAL VOLUME WHEN MEASURING BODY COMPOSITION BY HYDROSTATIC WEIGHING

#### Presentation Type

Presentation

#### Abstract

Residual volume (RV), the air left in one’s lungs, is an important factor when calculating percent body fat (%BF) using hydrostatic (underwater) weighing and needs to be estimated accurately. Hydrostatic weighing is the gold standard for determining %BF but is often done with an estimate of RV rather than actual measurement. PURPOSE: The purpose of this study is to evaluate the efficacy of estimating residual volume. METHODS: One hundred and forty-seven subjects (n=71 males, n=76 females) participated in this study. Height, weight in air, hydrostatic weight and RV by nitrogen washout was measured on all subjects. %BF was then calculated using the Siri equation using both measured and estimated RV values. A 2 tailed t-test was done to assess the difference between the %BF values determined when using estimated or measured RV. RESULTS: There was a significant difference between the two residual volume methods (Using est. RV, %BF=18.3 ± 7.4% vs. using measured RV, %BF=19.8 ± 8.0%, p<0.05). CONCLUSION: This data suggests that using the current equation to estimate RV when calculating %BF is not a reliable method for exact determination of %BF, but is a reasonable estimate and only over estimated by about 1.5% on average. This equation should be re-evaluated to better accommodate the current populations who are more obese than when the original Quanjer RV estimate formulas were developed.

#### Category

Life Sciences

ESTIMATED VS. ACTUAL RESIDUAL VOLUME WHEN MEASURING BODY COMPOSITION BY HYDROSTATIC WEIGHING

UC 327

Residual volume (RV), the air left in one’s lungs, is an important factor when calculating percent body fat (%BF) using hydrostatic (underwater) weighing and needs to be estimated accurately. Hydrostatic weighing is the gold standard for determining %BF but is often done with an estimate of RV rather than actual measurement. PURPOSE: The purpose of this study is to evaluate the efficacy of estimating residual volume. METHODS: One hundred and forty-seven subjects (n=71 males, n=76 females) participated in this study. Height, weight in air, hydrostatic weight and RV by nitrogen washout was measured on all subjects. %BF was then calculated using the Siri equation using both measured and estimated RV values. A 2 tailed t-test was done to assess the difference between the %BF values determined when using estimated or measured RV. RESULTS: There was a significant difference between the two residual volume methods (Using est. RV, %BF=18.3 ± 7.4% vs. using measured RV, %BF=19.8 ± 8.0%, p<0.05). CONCLUSION: This data suggests that using the current equation to estimate RV when calculating %BF is not a reliable method for exact determination of %BF, but is a reasonable estimate and only over estimated by about 1.5% on average. This equation should be re-evaluated to better accommodate the current populations who are more obese than when the original Quanjer RV estimate formulas were developed.