Intrinsic Mode Entropy for postural steadiness analysis

Postural balance during quiet standing is maintained by complex interactions of many sensory systems, including visual, vestibular, and proprioceptive systems. It has been demonstrated that applying vibration to the tibialis anterior tendon when subjects are in a static upright position creates an illusion of body inclination, thus decreasing postural stability. Postural balance was evaluated using centre of pressure (COP) displacements measured using a force plate. Recently, Intrinsic Mode Entropy (IMEn) has been proposed to quantify the degree of regularity and complexity in nonlinear signals. IMEn can be considered as an extension of Sample Entropy (SampEn) to deal with different oscillation levels. The first step of IMEn consists of extracting the Intrinsic Mode Functions (IMFs) of a time-series using Empirical Mode Decomposition (EMD). The IMEn is then obtained by computing the SampEN of the cumulative sums of the IMFs.