A second method used to analyze body composition is multi-frequency BIA (MF-BIA). This method models the body more accurately as a parallel RC circuit with resistive ECW on one branch and resistive ICW and cell capacitance on the second branch [Fig. 1(a)]. Impedance measurements are made over a range of frequencies, the assumption being that ECW is measured at low frequencies when cell membranes block current, and total body water is measured at high frequencies when current passes through cell membranes, traversing both ICW and ECW. A third method is known as Bioelectrical Impedance Spectroscopy (BIS), which makes use of the Cole model.9,14 In this approach, body impedance is also measured over a range of frequencies. For each frequency the series equivalent circuit for the circuit in Fig. 1(a) is found and the effective reactances and resistances are graphed using a Cole- Cole plot. Information from this graph is then used to calculate both ECW and ICW. Although BIA is used in general for hydration assessment in athletes, nutritional analysis, and to characterize body fluid levels for ill patients such as those in renal dialysis, the method of BIA used depends on the application.13 For exam- ple, ECW may be better analyzed by MF-BIA than SF-BIA,