Frequency analysis approach to study balance control in individuals with multiple sclerosis.

Background: The ability to control balance is often compromised in people with multiple sclerosis (MS) and is considered to be a strong contributing factor toward their increased risk of falls.

New Method: The aim of the study was to demonstrate that frequency analysis of postural sway could be used to investigate postural control in people with MS. Ten individuals with MS and ten age-and-gender matched healthy subjects stood on the force platform with eyes open or closed. The displacements of center of pressure (COP) were used to calculate power spectrum using fast Fourier transform. Power spectrum was analyzed for anterior-posterior (AP) and medial-lateral (ML) directions using three frequency bands: 0-0.3 Hz, 0.3-1 Hz, and 1-3 Hz reflecting contributions from the visual, vestibular/somatosensory, and proprioceptive systems, respectively.

Results: The mean COP velocity in the eyes closed condition was significantly larger for the MS than the healthy control group. Additionally, the MS group showed a significant decrease in the magnitude of COP power spectrum in the low frequency band and a pattern of increase in the medium and high frequency bands in the medial-lateral direction.

Conclusion: The observed redistribution of the COP power spectrum when vision is absent indicates that people with MS relied more on the vestibular/somatosensory and proprioceptive systems. However, such a strategy change was ineffective in maintaining postural stability, thus highlighting the impaired ability of the somatosensory system in regulation of postural control in people with MS. The outcome of the study suggests that the COP frequency analysis could be used in identifying the possible sources of balance impairment in people with MS.