Article

Force-plate posturography is a simple method that is commonly used in the
contemporary laboratory and clinic to assess postural control. Despite the
obvious advantages and popularity of the method, universal standards for
posturographic tests have not been developed thus far: most postural assessments
are based on the standard spatiotemporal metrics of the center-of-foot pressure
(COP) recorded during quiet stance. Unfortunately, the standard COP
characteristics are strongly dependent on individual experimental design and are
susceptible to distortions such as the noise of signal digitalization, which
often makes the results from different laboratories incomparable and unreliable.
The COP trajectories were recorded in subjects standing still, with eyes open
(EO) and then, with eyes closed (EC). The 168 subjects were divided into 3
experimental groups: young adults, older adults, and patients with Parkinson's
disease. Three novel output measures: the sway directional index (DI), the sway
ratio (SR), and the sway vector (SV) were applied to assess the postural
stability in the experimental groups. The controlled variables: age, pathology,
and visual conditions, uniquely affected the output measures. The basic
attributes of the SV: its reference position, magnitude, and azimuth, provided a
unique set of descriptors for postural control that allowed me unambiguously to
differentiate the decline in postural stability caused by natural ageing and
Parkinson's disease. As shown in previous investigations, the SV attributes, when
optimally filtered with a low-pass filter, were highly independent of the trial
length and the sampling frequency, and were unaffected by the sampling noise. In
conclusion, the SV may be recommended as the useful standard in static
posturography.
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