Impedance values in the arms and legs generally range between 200 and 500Ω, while the values for the trunk are between 20 and 30Ω. Despite its low impedance, the trunk accounts for 50% of lean body mass. Because the impedance values for the arms and legs range in the hundreds, an error of 1 to 2Ω will have a negligible effect on the final measurement. However, a 1 to 2Ω error in the trunk can cause significant miscalculations when determining results for the trunk. Therefore, overall body composition can only be accurately calculated when even slight changes in the impedance of the trunk can be detected. For this reason, accurate and direct trunk measurements are essential for determining body composition.

InBody’s patented design separates the current-emitting and voltage-detecting electrodes, which allows impedance to be measured in the area where current flow and voltage measurement overlap. Using DSM-BIA, InBody can determine the impedance values of the arms, legs, and trunk. This technology was first developed by InBody and is protected by patents in various countries around the world.

Conventional BIA devices, by contrast, employ the “Whole Body Impedance” measurement method, which only reports a single impedance value for the entire body. This is an imprecise and dated method because it cannot directly measure trunk impedance, which is essential for accurate measurements.