In biological systems, electrical conduction is related to water and ionic distribution in the conductor. Because fat-free mass, which includes the protein matrix of adipose tissue, contains virtually all the water and conducting electrolytes in the body, conductivity is far greater in the fat-free mass than the fat mass of the body. This hypothetical relationship was proposed by Nyboer et al., who demonstrated that electrically determined biological volumes (V) were inversely related to resistance (R), and reactance (Xc). Because the magnitude of reactance is small relative to resistance, and resistance is a better predictor of impedance than is reactance, the expression for V becomes: V = pL2/R, where R is in ohms.