Evaluation of spectral characteristics of physiological tremor of finger based on mechanical model.
A mathematical model for a physiological tremor of a finger, hereafter referred to as tremor, has been developed in order to evaluate the variation of amplitudes and frequencies at two peaks obtained in the power spectrum of the tremor under two conditions: (a) four loads of weight, 50, 100, 150, and 200 g, are added to the finger (state of load of weight), and (b) the finger is held in a horizontal position with a weight of 200 g for ten minutes (state of fatigue). The mathematical model for the tremor consists of a mechanical system of the finger and a reflex feedback system via the spinal and the supraspinal pathways. In the condition of the load of the weight, the two peaks shown in the tremor spectrum at about 10 Hz and 25 Hz under the condition of no load are generated by the existence of the spinal and the supraspinal pathways. The variation of the frequencies at the two peaks due to the load of the weight, which is not obtained by the previous model (Sakamoto et al., 1998), is possible to evaluate by use of the reflex feedback system which includes the terms up to the second order derivative. The amplitudes at the two peaks of the tremor spectrum increase with the additional weight on the finger because of the increase of the activity level of the active element of muscles controlling the finger. This element is one of the sub-systems constituting the tremor model. Because the activity level of the active element corresponds to the contraction force produced by the muscles, the increase of the amplitudes at the two peaks results from the progress of the recruitment of the motor unit activity by the addition of the weight. The term presenting the activity level is here introduced in the tremor model, so that the phenomenon is found. In the condition of the state of fatigue, the amplitudes at the two peaks increase with the progress of the fatigue because the active element is presented as a function of the time course, so that the activity level of the active element increases with the time course. The increase of the activity level implies the progresses of the recruitment and synchronization of the motor unit activity due to the fatigue. These results obtained from the analysis of the tremor model verify the hypothesis that the amplitude of the tremor oscillation is attributable to the changes of the activity of the spinal and the supraspinal systems.
Arihara
M
M
Department of Communications and Systems, University of Electro-Communications, Tokyo, Japan.
Sakamoto
K
K
D000465:Algorithms; D005069:Evaluation Studies as Topic; D005246:Feedback / Q000502:physiology; D005385:Fingers / Q000294:innervation / Q000503:physiopathology*; D006801:Humans; D008954:Models, Biological; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D009434:Neural Pathways / Q000503:physiopathology; D009991:Oscillometry; D011999:Recruitment, Neurophysiological / Q000502:physiology; D012018:Reflex / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013116:Spinal Cord / Q000503:physiopathology; D013314:Stress, Mechanical; D009435:Synaptic Transmission / Q000502:physiology; D013997:Time Factors; D014202:Tremor / Q000503:physiopathology*; D016474:Weight-Bearing / Q000502:physiology