Application of a chatic stimulation to development of a chair free from backache

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Vehicles such as airplane, railway and automobile are used for a long distance transportation. During the transportation, passenger is enforced to have a tightened posture especially in the airplane. Therefore, passenger will be affected to a painful stress in muscles of the body. Physical stress in the human body sometimes will happen to be serious hazard to health. To release the stress on the muscle, recently, relaxation machine is introduced with facility of a finger pressure therapy. In the therapy, the body can get a relaxed condition knocked by a fist.This study presents the results of biological signal analysis in human body subjected to periodic and chaotic knocked-stimulation. Electrical signals on a skin of the body are measured. An electricalcardiogram(ECG) is detected from a chest of the body. The signal of an electromyogram (EMG) is measured from muscles of both arms. The maximum Lyapunov exponent is calculated for the signal under test. Using the Karhuen-Loeve transformation (Principal Component Analysis), contributions to the signal of the body under the external stimulation are clarified.It is found that the followings ;1. When the quick periodic knocking is applied to the body, cardiac beat of the heart increases to higher frequency.2. When the body is stricken quickly by the knocking machine, the maximum Lyapunov exponent of the EMG decreases to lower value compared to those of slow knocking condition and the quiet condition. The number of physical parameter contributed to the EMG decreases. It shows that the quick stimulated forces to the body will produce a steady-state periodic response with lower degree of freedom.3. Under three testings of quiet condition, periodic knocking and chaotic excitation, the signals of the ECG show more complex unsteady behavior than that of the responses of EMG.4. Comfortable excitation to the body is found to be the chaotic stimulation by the test in our experiment.