Since the first measurements of tremors it was obvious that the tremor
signal originates from very complicated and continuously changing ner
vous and mechanical factors. However, the tremors originate in the beg
inning from the action tremors of the skeletal muscles. In this study
the basic structure of the action tremors, regular 13-Hz oscillations,
was revealed (measured by an accelerometer fixed on the distal end of
the muscle belly of the M. brachioradialis). The mechanical oscillati
ons measured with this technique had a linear relationship to the elec
trical oscillations of the EMG. Further, harmonic interference of isom
etric contraction with faradic contraction was observed. During simult
aneous contraction of neighbouring muscles, completely synchronous but
exactly out-of-phase oscillations were observed.