Distribution of tremorogenic activity among the major superficial muscles of the upper limb in persons with Essential tremor

Abstract

Objective: Peripheral tremor suppression has the potential to reduce tremor, but we do not currently know where best to intervene. The purpose of this study was to characterize the distribution of tremorogenic activity among upper-limb muscles.

Methods: Surface electromyography was recorded from the 15 major superficial muscles of the upper limb while 25 patients with Essential Tremor performed postural and kinetic tasks. We defined tremorogenic activity as power in the tremor band (4-8 Hz) and determined the distribution of this power among muscles.

Results: The distribution varied considerably between patients (mean r = 0.58), but on average, the greatest power was found in the anterior deltoid and extensor carpi ulnaris muscles. Other muscles with high power included the extensor carpi radialis, pectoralis major, lateral deltoid, and brachialis muscles. This distribution was similar (mean r ≥ 0.88) for postural and kinetic tremor, various limb configurations, repetitions, and patient characteristics (sex, tremor severity, age of onset, and duration).

Conclusions: We identified a rough pattern in which muscles opposing gravity appeared to have the highest tremor-band power; we hypothesize that the distribution of tremorogenic muscle activity depends in part on the distribution of voluntary activity required by the task.

Significance: Understanding which muscles exhibit the most tremorogenic activity is one of the steps in the pursuit of optimizing peripheral tremor suppression.

Keywords: Distribution; EMG; Essential tremor; Muscle; Tremorogenic; Upper limb.