The second basic mechanism of tremor is a transmission of oscillatory activity from the central nervous system to muscles in the periphery. The rhythmic activity of muscles then leads to tremor. In contrast to mechanical-reflex oscillations, central oscillations occur at a centrally determined frequency and are independent of the limbs’ mechanics. This crucial difference between the two basic mechanisms can be used to distinguish them from one another.

For example, limb mechanics can easily be influenced by loading the limb being studied, just as weighting slows down a clock pendulum. Increasing weight leads to a decrease in resonant frequency, and therefore:

Note that the mechanical loading approach to distinguish the two types of oscillations has its limitations. The greater the involvement of reflex pathways in mechanical-reflex tremors, the lesser the role that limb mechanics play in the frequency of tremor. If reflex pathways are important, then the frequency is more dependent upon reflex arc length, which differs between distal and proximal muscles, and therefore the frequency will also differ between different muscle groups. ET is characterized by uniform frequencies throughout the body, a further argument for a central oscillator involved in the generation of ET.


1. Raethjen J, Deuschl G. Handbook of Essential Tremor and Other Tremor Disorders. (Lyons KE, Pahwa R, eds.). Taylor & Francis; 2005.