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Parameterization of the Tremor Signal from Accelerometers in Multiple Sclerosis

Tremor, an involuntary and rhythmic oscillatory movement of a part of the human body, is a part of complex movement disorder in multiple sclerosis (MS). This paper aims to investigate possible parametrizations of the signal from accelerometers and find the parameters that are significantly different in the group of healthy persons and MS patients. A postural tremor was measured for each patient during the experiment using our device equipped with a 3-axis accelerometer. The group of MS patients consists of 24 probands (7 males and 17 females); the average age was 49.6 ± 12.5 years (mean ± standard deviation). The group of healthy control subjects consists of 28 probands (16 males and 12 females, the averaged age is 41.8 ± 18.5 years). Several parameters were specified and evaluated in the study: the maximum value of power spectral density (PSD) of the signal, the frequency of maximum value in PSD, the total power spectral density in a specific frequency band (fixed or variable). The differences in MS patients' parameters and healthy controls were evaluated using box-plots and statistical evaluations such as a two-sample t-test, the Kolmogorov-Smirnov test, the Lilliefors of normality and the Mann-Whitney (Wilcoxon) test. The maximum value of PSD and the cumulative value of PSD in the fixed frequency range have been recognized as parameters with a significant difference between the MS patients and the healthy population (p < 0.01).