Hydrostatic weighing at residual volume and functional residual capacity

both residual volume (RV) and functional residual capacity (FRC) to determine if underwater weighing at different lung volumes affected the measurement of body density. Subjects were 43 males, 18-25 yr. Subjects were submerged in the prone position, and the lung volume was measured by helium dilution at the time of the underwater weighing. Underwater weight was first assessed at FRC followed by assessment at RV. Changes in lung volume were accurately reflected in the underwater weight. Body density (D) was not different with the use of the FRC (mean D = 1.0778) or RV (mean D = 1.0781) data. Percent fat values for the FRC and RV data were 9.3 k 5.4 and 9.2 k &I%, respectively, and were not statistically different. The results indicate that the difference between percent fat deter-minations by HW in the prone position at FRC and RV is negligible, Because measurement of underwater weight at FR