A Comparison of the Effects of Measured, Predicted, Estimated and Constant Residual Volumes on the Body Density of Male Athletes

Abstract

The aim of this study was to use the measured residual volume (RV) of male athletes (n = 207) as a criterion and assess the error in their RV, body density (BD) and relative body fat (% BF) associated with using RVs predicted from regression equations, RVs estimated from vital capacity (VC) and an assumed constant RV of 1300 ml. The ventilated residual volume (RV) was determined both before and after the underwater weighing by helium dilution with the subject immersed to neck level. The mean of the absolute differences Idl̄ and SEE between the 2 RV trials were 66 and 89 ml, respectively. These increased to values ranging 195-747 and 259-308 ml, respectively, when the means of the 2 RV trials for each subject were compared with the RVs predicted via regression equations, estimated from the VC and assumed to be a constant of 1300 ml. A similar trend emerged with variation of only the RV in the BD formula for each subject. The 2 RV trials resulted in a Idl̄ and SEE of .00109 (.5% BF) and .00145 g·cm^-3 (.6% BF), respectively, but these increased to values ranging .00306 (1.3% BF) - .01207(5.1% BF) and .00394(1.7% BF) - .00441 g·cm^-3 (1.9% BF), respectively, for predicted, estimated and assumed constant RVs. In all cases the lowest Idl̄ and SEE were associated with the RVs predicted by a multiple regression equation (R = .616; SEE = 259 ml) which was generated on our sample. These data indicate that the use of predicted, estimated and constant RVs can result in substantial errors in the determination of BD, and hence in the estimation of % BF, compared with those when the RV is measured.

Measured residual volume: predicted - estimated and constant residual volumes - body density