Stiffness of human tibialis anterior muscle was measured at rest as well as at voluntary contraction by using a newly developed device. The principle of this device is based on the following : When the mechanically vibrating system in this device is pressed to the subject, the resonance frequency of the vibrating system changes by depending upon the stiffness of the subject. Hence stiffness of the subject can be obtained by measuring this resonance frequency.
After several basic parameters, such as the optimal initial bias pressure and the range of vibration in the muscle, were investigated, the following experimental results were obtained.
1. The muscle stiffness increased along with increase of the tension, although the relation between them was not linear.
2. There was a good correlation between the values of stiffness indicated by this device and the subjective sensation of'consistency'of the muscle at various degrees judged by palpation of the muscle with fingertips of experimenters. This result indicates that this device is a useful instrument to measure muscle stiffness non-invasively.
3. When the muscle tension was held constant for several minutes, the values of stiffness gradually increased along with the amplitudes of integrated EMG.

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There are three dispersions in the electrical properties of living tissues. They are α, β andγ dispersions. β dispersion is the relaxation phenomenon related to the structure of tissues between about 1 kHz and 1 MHz in frequency. In this frequency range, the electrical equivalent circuit of legs is represented with two resistances and a capacitance. One of these resistances is related to the intracellular fluid resistance and the other, to the extracellular fluid resistance. The capacitance shows the capacity of cell membrane. Therefore, from the frequency characteristics near the β dispersion, we can get much useful information related to the structure of tissues. For example, the information includes the ratio of intracellular fluid volume and extracellular fluid volume, the electrical properties of cell membrane, and etc. Under this equivalent circuit, we analyzed the electrical impedance of legs theoretically and experimentally.
From the results, it has been concluded that
(1) the electrical impedance of legs shows the β dispersion between 30 kHz and 50 kHz in frequency,
(2) the relaxation time constants are not represented by only one value but are distributed,
(3) the electrical equivalent circuit of legs is shown by two resistances and a capacitance,
(4) one of these resistances is related to the intracellular fluid volume and the other, to the extracellular fluid volume, and
(5) it is useful to apply this impedance method to clinical diagnoses, for example, to monitoring of dialysis, diagnosis of cardiac failure, pulmonary oedema, etc.

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The phase transition curve (PTC) can generally be used to investigate the properties of the stable biological oscillators. Assuming that a neural oscillator controls the human finger tapping, its properties were studied by using PTCs which were obtained in psychological experiments. For example, the degree of functional interactions between the left and the right hand motor systems was examined and it was revealed that the interaction could be decreased by training.

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A viscoelastic model of the skeletal muscle consisting of contractile component and viscous and elastic components of the resting and contracting states is devised. Parameter values of all the components are determined from the physiological observations made on frog semitendinosus muscle (fiber bundle) in Ringer's solution at 10°C. Series elasticity at the contracting state increases with an increase in tension, the viscoelasticity of the resting muscle being constant. The contractile component obeys the force-load-velocity relation, so that the apparent viscous coefficient increases with exerting contractile force. Tension responses to ramp-wise stretch of the muscle are calculated on a digital computer, and a close agreement is shown between the experimental and simulated results. The model is feasible to explaining such nonlinear characteristics as the mechanical property of the contracting muscle varying with time after stimulus and with exerting force.

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This paper describes a new design technique of a real time phaseless filter, with analog filters and digital delay circuit, and its application to ECG recording.
To suppress motion or respiratory artifacts in ECG, it is common to use analog high-pass filters, but considerable waveform distortion is caused by non-constant group delay. On the other hand, phaseless filters have zero phase and can realize higher order and sharp cut-off frequency high pass filters without phase distortion. The distortion of ECG waveform through analog and phaseless filters are computed and compared by computer simulation.

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