Multiple sclerosis affects the frequency content in the vertical ground reaction forces during walking

Abstract

Background: Multiple sclerosis is a progressive neurological disease that results in a high incident of gait disturbance. Exploring the frequency content of the ground reaction forces generated during walking may provide additional insights to gait in patients with multiple sclerosis that could lead to specific tools for differential diagnosis. The purpose of this study was to investigate differences in the frequency content of these forces in an effort to contribute to improved clinical management of this disease.

Methods: Eighteen patients and eighteen healthy controls walked across a 10 meter long walkway. The anterior-posterior and vertical ground reaction forces generated during the stance phase of gait were evaluated in the frequency domain using fast Fourier transformation. T-tests were utilized for comparison of median frequency, the 99.5% frequency, and the frequency bandwidth between patients and healthy controls and also for comparisons between patients with mild and moderate severity.

Findings: Patients with multiple sclerosis had significantly lower 99.5% frequency (P=0.006) and median frequency (P<0.001) in the vertical ground reaction force. No differences were found in the anterior-posterior reaction force frequency content. There were no differences between patients with mild and moderate severity.

Interpretation: The lower frequency content suggests lesser vertical oscillation of the center of gravity. Lack of differences between severities may suggest presence of differences prior to currently established diagnosis timelines. Analysis of the frequency content may potentially serve to provide earlier diagnostic assessment of this debilitating disease.

Figure 1

A) Artificial signal resulting from summation of three different sine waves occurring with different frequencies and amplitudes. B) Signal from 1a broken down into its three component sine waves. In this manner it is much easier to see the dominant large amplitude sine wave as well as the higher frequency waves contributing to the summed signal. C) Power spectrum of artificial signal (Fig 1A) shows plot of frequency vs. amplitude for 3 sine waves in decomposed signal (Fig 1B).