Essential tremor (ET) is one of the most common movement disorders. The clinical heterogeneity of ET has been studied for many years, however, there are practically no comprehensive studies dedicated to the assessment of biochemical and electrophysiological parameters associated with the severity of motor and non-motor disorders present in patients with ET and taking into account their heterogeneity.
The objective of this report is to differentiate subgroups of essential tremor using cluster analysis of clinical, biochemical and electrophysiological parameters.
The study enrolled 90 patients with ET. Clustering was perform on the demographic data, scores of scales FTMS, ADL, MoCA, Beka, surface electromyographic data, levels of serum IL-1β, IL-6, IL-8, IL-10, TNFα, uric acid, ceruloplasmin, MDA.
Based on the analysis of the severity of motor manifestations, the psychoemotional state, the adaptive potential of patients and the biochemical aspects of the pathogenesis, three relatively homogeneous clusters of ET were identified.
Revealing the heterogeneity of essential tremor allows to expand understanding the pathogenesis of disease.

BACKGROUND: In order to alleviate muscle fatigue and improve ride comfort, many published studies aimed to improve the seat environment or optimize seating posture. However, the effect of lumbar support on the lumbar muscle of seated subjects under whole body vibration is still unclear.
OBJECTIVE: This study aimed to investigate the effect of lumbar support magnitude of the seat on lumbar muscle fatigue relief under whole body vibration.
METHODS: Twenty healthy volunteers without low back pain participated in the experiment. By measuring surface electromyographic signals of erector spinae muscles under vibration or non-vibration for 30 minutes, the effect of different lumbar support conditions on muscle fatigue was analyzed. The magnitude of lumbar support d is assigned as d1= 0 mm, d2= 20 mm and d3= 40 mm for no support, small support and large support, respectively.
RESULTS: The results showed that lumbar muscle activation levels vary under different support conditions. For the small support case (d2= 20 mm), the muscle activation level under vibration and no-vibration was the minimum, 42.3% and 77.7% of that under no support (d1= 0 mm). For all support conditions, the muscle activation level under vibration is higher than that under no-vibration.
CONCLUSIONS: The results indicate that the small support yields the minimum muscle contraction (low muscle contraction intensity) under vibration, which is more helpful for relieving lumbar muscle fatigue than no support or large support cases. Therefore, an appropriate lumbar support of seats is necessary for alleviating lumbar muscle fatigue.