Centre of pressure in dynamic posturography: a comparison among systems based on a pressure matrix and a force platform

The centre of pressure (CoP) measurement is a very important evaluation tool in posturography. Several papers have been focused on the estimation of CoP accuracy with a pressure matrix (PM) and a force platform (FP) in static conditions, while a few works reported analyses in dynamic conditions. Here, the previous sensors were compared in terms of relative and absolute error during two dynamic sessions: with a rigid bipod and with a healthy adult. Trials were conducted placing the PM and FP in series over a three-axial rotating base, programmed with sinusoidal trajectories of amplitude 10° and frequencies 0.2 Hz and 0.5 Hz. In order to compute the absolute errors of the PM and FP, a further estimation of the bipod CoP was done from the moving base rotation and bipod position gathered by an optoelectronic system. The CoP relative error between the two sensors was about 7–8 mm. Because the relative errors obtained during the bipod session were comparable with the ones obtained during the subject sessions, the absolute errors estimated with the bipod, <7 mm, can be reasonably extended to the dynamic posturography tests performed with the subject. The accuracies were estimated checking all the possible error sources, such as the sensors' alignment and the inertial artefacts; because these are rarely considered parameters in clinical routine, they can decrease the overall CoP accuracy if not carefully controlled.