Influence of location of acceleration sensor on physiological tremor of upper limb

The physiological tremor of the upper limb in three positions of pronation, neutrality, and supination due to the movement of forearm was measured on four locations at the tip of the finger, the root of the finger in the hand, the wrist, and the elbow with use of an accelerated sensor. The evaluation of the total power, which was the summation of the power spectrum in the frequency range from 1 to 50 Hz, showed no significant difference in any of the positions. The maintenance of the upper limb at the horizontal level showed the coordination of the central nervous system due to the body parts of the upper arm, forearm, hand, and finger connected by the joint. The coherence spectra showed clear activation of the joint of the wrist in the main peak frequency of around 2.5 and 12.5 Hz in their respective positions. The value of the correlation coefficient in the location between the hand and finger was the largest at over 0.8, and those of the locations which connected the joint of the wrist between the forearm and hand and between the forearm and finger were significantly large with a value from 0.6 to 0.8. The mean time (i.e., arrival time) of the transmission from the proximal side (i.e., upper arm and forearm) to the distal side (i.e., hand and finger) in the upper limb was evaluated quantitatively to be 20 ms for pronation and supination, but the value was small for neutrality.