Estimation procedures affect the center of pressure frequency analysis

Abstract

Even though frequency analysis of body sway is widely applied in clinical studies, the lack of standardized procedures concerning power spectrum estimation may provide unreliable descriptors. Stabilometric tests were applied to 35 subjects (20-51 years, 54-95 kg, 1.6-1.9 m) and the power spectral density function was estimated for the anterior-posterior center of pressure time series. The median frequency was compared between power spectra estimated according to signal partitioning, sampling rate, test duration, and detrending methods. The median frequency reliability for different test durations was assessed using the intraclass correlation coefficient. When increasing number of segments, shortening test duration or applying linear detrending, the median frequency values increased significantly up to 137%. Even the shortest test duration provided reliable estimates as observed with the intraclass coefficient (0.74-0.89 confidence interval for a single 20-s test). Clinical assessment of balance may benefit from a standardized protocol for center of pressure spectral analysis that provides an adequate relationship between resolution and variance. An algorithm to estimate center of pressure power density spectrum is also proposed.

Validation of Different Filters for Center of Pressure Measurements by a Cross-Section Study

“…Based on these findings, it can be assumed that the results of the CoP measurements become more stable with increasing measurement time and are subject to less fluctuation [6]. The investigations of Vieira et al also arrived at a similar conclusion [7]. In line with this, van der Kooij et al (2011) showed that with a shorter measurement time, the results of the frequency-dependent parameters are larger.…”

Do quiet standing centre of pressure measures within specific frequencies differ based on ability to recover balance in individuals with stroke?

“…Future work should seek to confirm this value as the most appropriate for a cut-off level. In addition, it has been suggested that the majority of the power in the COP spectrum lies within a range of DC to between 1.00-1.40 Hz, depending on the measurement methodology (Vieira et al, 2009). Therefore, the highest frequency range analyzed (1.60-3.20 Hz), although statistically different between groups, may have limited practical significance.…”

Parameter Reduction in the Frequency Analysis of Center of Pressure in Stabilometry

“…These studies analyze the frequency content of the whole measurement using Power Spectral Density (PSD) [12,13,20]. These studies often examine the median frequency (MDF) [21,22], mean power frequency (MPF) [15,20,23] and bandwidth (BW) [15,23] of the CoP signals in AP and ML directions. Further analyses concern the power ratios of different frequency bands on the power spectrum of CoP signals, revealing differences in the frequency content of eyes closed and eyes open bilateral standing conditions in people with multiple sclerosis [24] or in athletes [5].…”

“…Further analyses concern the power ratios of different frequency bands on the power spectrum of CoP signals, revealing differences in the frequency content of eyes closed and eyes open bilateral standing conditions in people with multiple sclerosis [24] or in athletes [5]. Many frequency-related posturographic parameters are highly sensitive to acquisition settings [25] and parameter settings of the different spectral estimators [21], with a resulting diversity in the results of the same measurements among different studies. Thus suggestions of standardized measurements and processing [21,25] as well as minimal acquisition criteria have been reported [26,27].…”

“…Many frequency-related posturographic parameters are highly sensitive to acquisition settings [25] and parameter settings of the different spectral estimators [21], with a resulting diversity in the results of the same measurements among different studies. Thus suggestions of standardized measurements and processing [21,25] as well as minimal acquisition criteria have been reported [26,27].…”