Mechanical and neural feedback factors in postural hand tremor of normal subjects.

Publisher Website
Google Scholar
Abstract
Acceleration tremors of the extended hand and surface EMG [electromyogram] of 2 extensor muscles were detected simultaneously for each of 9 normal subjects. The rms [root mean square] demodulated EMG amplitude at the major tremor frequency and the EMG-tremor coherence values were calculated with the assumption that the grouped electrical potentials at the tremor frequency resulted from neural feedback within the neuromuscular system controlling the hand. EMG-tremor coherence was generally high for all but the smallest amplitude (less than 100 .mu.m) tremors. For each subject, the relation between log(EMG) and log(displacement) was approximately linear, indicating that the demodulated EMG and the rms displacement of the tremor are related by a power function. For the 9 subjects, the tremor displacement increased approximately as the EMG squared. The power relation between EMG and tremor displacement indicates that the ratio of demodulated EMG to tremor displacement generally decreased with increasing displacement amplitude. The effect of mass loading of the hand on the tremor period appeared to depend on the displacement amplitude of the tremor. For small-displacement oscillations, mass loading increased the tremor period, as expected for a constant-spring, variable-mass system. For certain large-displacement tremors (and certain subjects), the tremor period was relatively independent of mass loading. The period of large-displacement tremors depended on hand position. Internal perturbations, muscle-load mechanics and neural feedback factors act together to determine the many different steady-state values of displacement amplitude and frequency of hand tremor.

This publication has 9 references indexed in Scilit: