Hilbert-Huang Transformation: Application to Postural Stability Analysis

The aim objective of this paper is the analysis of the centre of pressure (COP) time series by the means of the Hilbert Huang Transformation (HHT). The HHT consists of extracting the intrinsic mode functions (IMFs) from an empirical mode decomposition (EMD), and then applying the Hilbert transformation on the IMFs. The trace of the HHT in the complex plane has a circular form, with each IMF having its own rotation frequency. The area of the circle represents a possible indicator of the postural stability status of the subjects. Experimental results show the effectiveness of the area of this circle in order to identify the post-vibratory effects on standing posture in healthy adult subjects.