Figure 2.

Tremor analysis with an outstretched left arm. Activity in the muscles participating in the tremor can be recorded and analyzed. The upper tracing reveals synchronous, regular activity of the hand extensors and flexors. The spectrum has a peak at 4.3 Hz; the movement is thus rhythmic, satisfying the definition of tremor. The coherence curve shows that the activity of each of the two muscles at 4.3 Hz is correlated with the other. The phase information at 4.3 Hz in this case indicates that the muscles are active without any temporal delay between them (i.e., the phase difference here is zero). The finding of activity at 4.3 Hz with simultaneous innervation of agonist and antagonist muscles is typical of essential tremor.