Abstract
The body density (BD), and hence the relative body fat (% BF), was measured for 182
female athletes. The residual volume (RV) was determined both before and after the
underwater weighing by a multiple breath helium dilution technique with the subject
immersed to neck level. The absolute mean difference (|Xd|) and SEE between the two
RV trials were 63 and 75 ml, respectively. These increased to values ranging 144-685
and 187-252 ml, respectively, when the mean of the two RV trials for each subject
was compared with the RVs predicted via regression equations, estimated from the vital
capacity (VC) and assumed to be a constant of 1000 ml. A similar trend resulted from
variation of only the RV in the BD formula, for each subject. The two RV trials resulted
in an |X̄d| and SEE of .00121 (.5% BF) and .00141 g·cm-3 (.6% BF), respectively, but these increased to values ranging .00283 (1.3% BF) -.01291
(5.7% BF) and .00362 (1.6% BF) -.00527 g·cm-3 (2.5% BF), respectively, for predicted, estimated and assumed constant RVs. In all
cases, the lowest |X̄d| and SEE were associated with the RVs predicted by a multiple
regression equation (R=.725; SEE=187ml) which was generated on our sample while the largest |X̄d| values
were registered by the other regression equations. These data emphasize that the use
of predicted, estimated and constant RVs result in substantial errors in BD and %
BF compared with those when the RV is measured.
Key words
measured residual volume - predicted - estimated - constant residual volumes - body
density
