Basic aspects of action tremors in the human M. brachioradialis

Since the first measurements of tremors it was obvious that the tremor signal originates from very complicated and continuously changing nervous and mechanical factors. However, the tremors originate in the beginning 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 oscillations measured with this technique had a linear relationship to the electrical oscillations of the EMG. Further, harmonic interference of isometric contraction with faradic contraction was observed. During simultaneous contraction of neighbouring muscles, completely synchronous but exactly out-of-phase oscillations were observed.