Predictions of the existence, frequency, and amplitude of physiological tremor in normal man based on measured frequency-response characteristics.

Mathematical models for 1) musculoskeletal dynamics, and 2) reflex feedback, based on the results of the authors' frequency-response measurements on normal adult male human subjects, are combined to produce a model for physiological tremor in such subjects. An analysis of this model shows that the system will be unstable to small disturbances (that is, tremor will occur) under certain conditions of external loading. Further, when the system is unstable, nonlinearities in the model produce responses in the form of limit cycles, and both the frequency and amplitude of the resulting tremor can be calculated. For constant loads applied through a constant compliance, the model predicts the onset of tremor at low loads, a maximum intensity of tremor at loads corresponding to 30-50 percent of maximum voluntary effort, and a decrease in the tremor amplitude at still higher loads.