A new TOBEC instrument and procedure for the assessment of body composition: use of Fourier coefficients to predict lean body mass and total body water.

A second-generation total body electrical-conductivity instrument (TOBEC II) that uses convolution principles was evaluated. This study 1) examined the stability of the instrument, 2) validated the relationship of total body electrical conductivity to isotopically determined total body water (TBW) and densitometrically determined lean body mass (LBM), and 3) developed prediction equations for LBM, TBW, and total body potassium using Fourier coefficients. In a sample of 40 men and women aged 19-35 yr and ranging from 6% to 36% body fat, the correlations among the zero-, first-, and second-order Fourier coefficients (FC0, FC1, FC2) with LBM were r = 0.97, 0.98, and 0.99, respectively. Similarly, the correlations with TBW were r = 0.96, 0.97, and 0.98, respectively. The best prediction equation was for LBM: LBM (kg) = 22.998 + 0.102FC0 + 0.062FC1 - 0.29FC2(R2 = 0.983 and SEE = 1.43 kg).