Submitted to: North Dakota Academy of Science Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 10, 2003
Publication Date: April 27, 2003
Citation: Siders, W.A., Lukaski, H.C. 2003. Body, half-body, and presenting limb bone-free, fat-free weight: determinates of variability in bioelectrical impedance [abstract]. Proceedings of the North Dakota Academy of Science. v.57. p.34. Technical Abstract: The use of bioelectrical impedance analysis (BIA) to estimate body composition requires determining the impedance (Z, ohms) that the body offers to the conduction of an applied electrical current alternating and low level). Fat and bone tissues are thought to be relatively high contributors to impedance and bone-free, fat-free (BFFF) tissues (which contain a large portion of the body's water and electrolytes) are thought to contribute minimally to impedance (Lukaski, 1991). The purpose of this study was to determine whether the weight of the BFFF component of the body, half-body, or presenting limb accounted for more of the variability in the measured bioelectrical impedance. Sixty-two women and 48 men were measured for whole body R and Xc at 50 kHz (RJL Systems Quantum X) and for body composition by pencil beam dual x-ray absorptiometry (Hologic, Inc. QDR 2000). Impedance was measured with a varying tetrapolar placement of electrodes on the right hand and foot (right side), the left hand and foot, on both hands (upper body), or on both feet. Right and left body were defined by a midsagital plane. Upper and lower body were differentiated with a transverse plane just superior to the crests of the ileum. Participants ranged in age from 22-60 years with BFFF body from 29-79 kg and measured Z from 305-719 ohms. The mean of BFFF tissue was similar for right-to-left and upper-to-lower body and for right-to-left arm and leg. Women averaged about two-thirds as much BFFF tissue as men in the trunk, 50% as much in the arms, and 60% as much in the legs. The components of Z are resistance (R) and reactance (Xc): Z**2 = R**2 + Xc**2. Lukaski (2000) has reported that R represents more than 98% of the measured impedance of the body. Electrical conductor theory describes the relationship of impedance to conductor volume as Z = Rho L2 / V. We correlated the weight of BFFF tissue, which contains the major portion of the body water, with R, the commonly considered index of body water and the major component of Z. The correlation coefficients (r) for BFFF in the whole body, half body, presenting arm and presenting leg, with R when R was measured on the left side of the body were r = -0.830, -0.825, -0.796, and -0.823, respectively. When R was measured on the right side, r = -0.832, -0.838, -0.812, and -0.831, respectively. When R was measured across the upper body, r = -0.858, -0.862, -0.857, and 0.860, respectively. And when R was measured across the legs, r = -0.674, -0.683, -0.673, and -0.684, respectively. The contribution of BFFF tissue to variability in R was not very different as a function of presenting body segment source. The contribution of BFFF to variability in R was lower when R was measured across the legs. Foot-to-foot measurement of R may not be the method of choice for estimating body composition.