Standard versus modified bio-electrical impedance analysis on reactance measurements

The purpose of this investigation was to compare score consistency of the observed reactance measurements for total body composition bio-electrical impedance analysis (BIA), using standard and modified electrode placement procedures. Subjects were 80 military males (19-56 years) who volunteered from Elmendorf Air Force Base, Anchorage, Alaska. The RJL Systems Spectrum Lightweight Instrument was used. RJL's rules were followed for standard procedure, and the proximal electrode sites were changed for the modified procedure. The hand and foot proximal electrodes were placed in the center of the antecubital space and popliteal fossa, respectively. The study used a four-faceted crossed, random effects design. The object of measurement was person, and facets of generalization were day, occasion, and trial. Data were analyzed independently for each electrode placement procedure. The analysis revealed: 1) person contributed the largest source of systematic variance, as expected, and 2) person x day interaction accounted for the significant percentage of unwanted measurement error for both electrode placement procedures. The relative and absolute coefficients of the G-studies (80 persons x 2 days x 2 occasions x 3 trials) were 0.86 for standard and 0.83 for modified. The D-studies (111, 211, 311, and 511) revealed relative and absolute coefficients which ranged from 0.75 to 0.94 for standard, 0.67 to 0.91 for relative, and 0.67 to 0.90 absolute for modified. The G-coefficients (G study and D studies) for reactance measurements showed the standard electrode placement procedure produced more consistent scores than the modified proximal electrode placement procedure. In conclusion, generalizability analysis on reactance scores demonstrated the standard electrode placement procedure still to be superior over the modified electrode placement procedure.