The most validated method of obtaining TBW is single frequency BIA (SF-BIA).9 At a single frequency, the body can be represented as a simple circuit with a resistor representing the effective resistance of TBW in series with a capacitor representing cell membranes, as shown in Fig. 1(b). Body impedance is typically measured at 50 kHz and empirical relationships are used to derive fat-free mass (FFM) from the measured effective resistance. SF-BIA equations are empirical but are based on the relationship between the resistance R, resistivity q, and the dimensions of a cylindrical object as in