A statistical approach for studying the power spectrum of the center of pressure displacement for subjects in orthostatic posture

Abstract

Postural control assessment by visual feedback in health population is still controversial. This works aims at investigating the influence of the visual system on the power spectra estimates (Ŝ(f)) of the center of pressure displacement (COP) using two distinct protocols: eyes open (EO) and closed (EC). Subjects (N = 144) were submitted to stabilometric test, with 30 s in each eyes condition. Ŝ(f) was estimated for the anterior-posterior stabilometric signal using the Bartlett periodogram method for both eyes condition. The Spectral F-Test (SFT) was then applied to test the null hypothesis (H0) of same power contribution at each spectral frequency and in the frequency band Δf = 0.1-0.3 Hz. While for 69.4% of subjects H0 within this band has been accepted, for 40 subjects this hypothesis was rejected (SFT(Δf) < 0.06). In the latter cases, the Romberg quotient of the sway area of the bandpassed (0.1-0.3 Hz) signals resulted in higher values (median of 386.66) than that obtained without filtering. Thus, it is suggested the use of the spectral F-Test and band-pass filtering for assessing differences between the sway in different protocols. © Springer-Verlag Berlin Heidelberg 2007.