Measurements of body composition in limbs and trunk using a eight contact electrodes impedancemeter

Abstract 

Regional body composition measurements may be achieved in a single operation with impedancemeters equipped with four plantar and four hand electrodes. By measuring sequentially the resistances of five current lines connecting the hands and feet and solving a system of five linear equations, it is possible to calculate the resistances of each limb and the trunk. The impedancemeter used in this study was a prototype with four plantar electrodes and four additional contact electrodes for the hands. Its electronic hardware was identical to that of a Tefal commercial foot-to-foot impedancemeter (FFI). The Tefal FFI was used for measuring weight, whole body fat-free mass (FFM) and fat tissue mass (FM). Impedance and DXA measurements were taken sequentially on a 1st cohort of 170 healthy adults, aged from 19 to 75 years, to obtain equations relating appendicular FFM measured by DXA to their resistances, subject weight and height. For appendicular FM, correlations of the body FM measured by the FFI, age and BMI were used. Trunk FFM was obtained by subtracting appendicular FFM from FFM of trunk+limbs obtained by the same method as that for appendicular FFM. For an independent validation, these equations were tested on a 2nd cohort of 87 subjects (18–74 years) who underwent the same impedance and DXA protocol. Comparison of FFM and FM by impedance and by DXA in the limbs and the trunk using paired Student's t-tests, showed that they were not significantly different both in the 1st and validation cohorts. Mean FFM differences between impedance and DXA were −0.018±0.48kg for right arms and −0.039±0.85kg for right legs of men in validation cohort. This work confirms that eight contact electrodes bioimpedance can measure appendicular and trunk FFM and FM in good agreement with DXA, at least in a healthy population.

Keywords: Fat-free mass, Fat tissue mass, Segmental bioimpedance, Foot-to-foot impedancemetry