Bioelectrical impedance measuring device and measuring method

Abstract

To easily measure impedance inside a living body.SOLUTION: A pair of first electrodes 10 are disposed separately at a predetermined position of a living body. A pair of second electrodes 11 are disposed on a straight line connecting the pair of first electrodes 10 separately, and the pair of first electrodes 10 are disposed inside the pair of second electrodes 11. A pair of third electrodes 12 are disposed separately on the straight line connecting the pair of first electrodes 10, and the pair of second electrodes 11 are disposed inside the pair of third electrodes 12. An electric current I1 is applied to the living body by a first power source 13 through the second electrodes 11 to calculate impedance Zout. In the meanwhile, an electric current I2 is applied to the living body by a second power source 14 through the third electrodes 12 to calculate impedance Zall. Impedance Zin inside the living body is calculated by Zin=Zout×Zall / (Zout-Zall).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a bioelectrical impedance measuring device and method, and in particular to measuring internal impedance. [Background technology]

[0002] 2. Description of the Related Art A method is known in which an electric current is passed through a living body to measure bioelectrical impedance and thereby evaluate muscle mass and water content.

[0003] Patent document 1 describes a device that arranges a large number of electrodes in a circular ring shape to be in contact with a living body, passes a current through the living body from one pair of the electrodes, measures multiple voltages with the remaining electrodes, and performs calculations based on these measurement results to image the bioelectrical impedance distribution.

[0004] Non-Patent Document 1 describes a method of measuring bioelectrical impedance by a four-electrode method and evaluating the degree of muscle fatigue from the impedance before and after high-load muscle exercise. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-233619 A [Non-patent literature]

[0006] [Non-Patent Document 1] Todd J. Freeborn, Bo Fu, "Fatigue-Induced Cole Electrical Impedance Model Changes of Biceps Tissue Bioimpedance" Fractal Fract, Vol.2, No.4, 2018 Summary of the Invention [Problem to be solved by the invention]

[0007] The bioelectrical impedance that can be measured by the method of Non-Patent Document 1 is the impedance of the entire inside of the living body, but the impedance of the skin changes significantly depending on humidity. Therefore, it was difficult to measure only the impedance change of the muscle inside the living body using the method of Non-Patent Document 1. In particular, when the area of ​​the device is reduced, the current is concentrated on the surface of the living body, making it more difficult to measure the internal impedance.

[0008] In addition, the method of Patent Document 1 requires the placement of many electrodes over a wide area in order to image the internal impedance distribution, which leads to problems such as the large size and complexity of the device or system, and the large amount of calculation required.In addition, since the electrodes are close to each other, the current concentrates on the surface of the human body, and the measurement accuracy of the internal impedance decreases due to the fluctuation of the surface impedance.

[0009] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a measuring device and a measuring method that can easily measure impedance inside a living body. [Means for solving the problem]

[0010] No. One embodiment is a bioelectrical impedance measuring device characterized by having a pair of first electrodes to be contacted with a living organism, a second electrode which is a pair of electrodes to be contacted with the living organism, the second electrode being spaced apart on a line connecting the pair of first electrodes and arranged so that the first electrode of the pair is on the inside, and a third electrode which is a pair of electrodes to be contacted with the living organism, the second electrode being spaced apart on a line connecting the pair of first electrodes and arranged so that the second electrode of the pair is on the inside, and a measurement unit that passes a current through the living organism via the second electrode and measures the current value and measures the voltage value between the first electrodes to measure the impedance of the surface of the living organism, passes a current through the living organism via the third electrode and measures the current value and measures the voltage value between the first electrodes to measure the impedance of the entire cross-section of the living organism, and calculates the impedance inside the living organism from the impedance of the surface of the living organism and the impedance of the entire cross-section of the living organism.

[0011] No. In one embodiment, the measurement section may have one current source, and a switch that switches between a connection between the current source and the second electrode and a connection between the current source and the third electrode.

[0012] A second aspect of the present invention is a method for detecting a biological sample comprising: a pair of first electrodes to be brought into contact with a living body; a second electrode, which is a pair of electrodes to be brought into contact with the living body, and is arranged spaced apart on a straight line connecting the pair of first electrodes, with the pair of first electrodes being arranged on the inside; a third electrode, which is a pair of electrodes to be brought into contact with the living body, and is arranged spaced apart on a straight line connecting the pair of first electrodes, with the pair of second electrodes being arranged on the inside; Surface At the same time, a first current is applied to the Surface and interior a second current having a phase opposite to that of the first current is passed through the The first current and the second current are cancelled out on the surface of the living body. In this state Second current The bioelectrical impedance measuring device is characterized by having a measuring unit that measures a current value and a voltage value between the first electrodes to calculate impedance inside the living body.

[0013] In the present invention, the second electrode may have a linear shape extending in a direction perpendicular to the straight line connecting the pair of first electrodes.

[0014] In the present invention, the thickness of a part of a living body where the internal impedance is to be measured may be D1, and the distance between the third electrodes may be L1, so that 0.1≦L1 / D1≦5 is satisfied.

[0015] In the present invention, the thickness of the skin at the site of the living body where the internal impedance is to be measured may be D2, and the distance between the second electrodes may be L2, so that 0.1≦L2 / D2≦5 is satisfied.

[0016] In the present invention, the measurement section may evaluate the degree of muscle fatigue from a change in impedance inside the living body.

[0017] In the present invention, the measurement section may measure impedances inside the living body at different frequencies and evaluate the degree of muscle fatigue based on a change in the impedance ratio.

[0018] No. The third aspect is a method for measuring bioelectrical impedance, which comprises contacting a pair of first electrodes, a second electrode which is a pair of electrodes arranged at a distance on a line connecting the pair of first electrodes with the pair of first electrodes positioned on the inside, and a third electrode which is a pair of electrodes arranged at a distance on a line connecting the pair of first electrodes with the pair of second electrodes positioned on the inside, passing a current through the organism via the second electrodes and measuring the current value and the voltage value between the first electrodes to measure the impedance of the surface of the organism, passing a current through the organism via the third electrode and measuring the current value and the voltage value between the first electrodes to measure the impedance of the entire cross-section of the organism, and calculating the impedance inside the organism from the impedance of the surface of the organism and the impedance of the entire cross-section of the organism.

[0019] In a fourth aspect of the present invention, a pair of first electrodes, a second electrode that is a pair of electrodes arranged at a distance on a straight line connecting the pair of first electrodes and arranged so that the pair of first electrodes is on the inside, and a third electrode that is a pair of electrodes arranged at a distance on a straight line connecting the pair of first electrodes and arranged so that the pair of second electrodes is on the inside are brought into contact with a living body, and a biological signal is transmitted to the living body via the second electrode. Surface At the same time, a first current is applied to the Surface and interior A second current having a phase opposite to that of the first current is passed through the The first current and the second current are cancelled out on the surface of the living body. In this state Second current This is a method for measuring bioelectrical impedance, characterized in that the current value is measured and the voltage value between the first electrodes is measured to calculate the impedance inside the living body. Effect of the Invention

[0020] According to the present invention, impedance inside a living body can be easily measured. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing the configuration of a bioelectrical impedance measuring device according to a first embodiment. [Diagram 2]A diagram showing the structure of a living body's arm. [Diagram 3] Equivalent circuit of the arm of a living body. [Figure 4] FIG. 13 is a diagram showing a modified example of the first embodiment. [Diagram 5] FIG. 13 is a diagram showing a modified example of the first embodiment. [Figure 6] FIG. 13 is a diagram showing a modified example of the first embodiment. [Figure 7] FIG. 1 is a diagram showing current distribution in a cross section of a living body. [Figure 8] A diagram showing a biological model. [Figure 9] A diagram showing the equivalent circuit of a living body. [Figure 10] A diagram showing the Cole-Cole plot of bioelectrical impedance Z. [Figure 11] A graph showing the change in bioelectrical impedance Z before and after muscle fatigue. [Figure 12] A diagram showing an equivalent circuit of a living body taking into account complex impedance. [Figure 13] A diagram showing an example of calculating Zall, Zin, and Zout. [Figure 14] FIG. 1 is a diagram showing the configuration of a muscle fatigue level measuring device. [Figure 15] A diagram showing the results of current distribution inside a living body obtained by electromagnetic field simulation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] (First embodiment) Fig. 1 is a diagram showing the configuration of a bioelectrical impedance measuring device of the first embodiment. As shown in Fig. 1, the bioelectrical impedance measuring device of the first embodiment has a pair of first electrodes 10, a pair of second electrodes 11, a pair of third electrodes 12, a first current source 13, a second current source 14, a first ammeter 15, a second ammeter 16, a voltmeter 17, and a calculation unit 18. The first current source 13, the second current source 14, the first ammeter 15, the second ammeter 16, the voltmeter 17, and the calculation unit 18 correspond to the measurement unit of the present invention.

[0023] The first electrode 10 is an electrode that is brought into contact with a living body and is an electrode for measuring the voltage applied to the living body. The pair of first electrodes 10 are placed at predetermined positions on the living body, spaced apart from each other. The electrode has a circular shape. Alternatively, the electrode may have a rectangular, square, or other shape. The electrode material is Au, Al, Cu, Ag / AgCl, or the like.

[0024] The second electrode 11 is an electrode that is brought into contact with the living body and is an electrode for passing a current through the living body. The pair of second electrodes 11 are arranged apart from each other on a straight line connecting the pair of first electrodes 10, and are arranged so that the pair of first electrodes 10 are inside the pair of second electrodes 11. The shape and material of the electrodes are similar to those of the first electrodes 10.

[0025] The third electrode 12 is an electrode that is brought into contact with the living body and is an electrode for passing a current through the living body. The pair of third electrodes 12 are arranged apart from each other on a straight line connecting the pair of first electrodes 10, and the pair of second electrodes 11 are arranged inside the pair of third electrodes 12. The shape and material of the electrodes are similar to those of the first electrodes 10.

[0026] First current source 13 is a current source for passing a current through the living body via second electrode 11. Both ends of first current source 13 are connected to first ammeter 15 and second electrode 11, respectively. The current passed through the living body has a frequency of 1 kHz to 1 MHz and is 500 μA or less.

[0027] The second current source 14 is a current source for passing a current through the living body via the third electrode 12. Both ends of the second current source 14 are connected to the second ammeter 16 and the third electrode 12, respectively. The current passed through the living body is the same as that of the first current source 13, and has a frequency of 1 kHz to 1 MHz and is 500 μA or less. The current from the first current source 13 and the current from the second current source 14 are controlled so that they do not pass simultaneously, but only one of them passes. For example, the currents are controlled to pass alternately at intervals of 1 to 10 ms.

[0028] The first ammeter 15 is a device that measures the value of the current I1 that flows through the living body via the second electrode 11.

[0029] The second ammeter 16 is a device that measures the value of the current I2 that flows through the living body via the third electrode 12.

[0030] The voltmeter 17 is connected between the first electrodes 10 and is a device for measuring the voltage between the first electrodes 10 .

[0031] The calculation unit 18 is a device that calculates the internal impedance of the living body from the current value measured by the first ammeter 15 and the second ammeter 16 and the voltage value measured by the voltmeter 17, and evaluates the degree of muscle fatigue. The details will be described later.

[0032] Next, a method for measuring bioelectrical impedance in the first embodiment will be described.

[0033] Figure 2 shows the structure of a living body's arm, and Figure 3 shows its equivalent circuit. As shown in Figure 2, the arm of a living body has a bone in the center, muscle around it, a layer of fat on the outside of the muscle, and skin on the outside of the fat. Therefore, the impedance of the entire arm of a living body can be approximated by the parallel impedance of the skin impedance, fat impedance, muscle impedance, and bone impedance. Of these, the conductivity of fat and bone is lower than the others. Therefore, as shown in Figure 3, it can be further approximated by the parallel impedance of the skin impedance and muscle impedance.

[0034] During muscle movement, a large amount of blood flows into the muscle, causing a change in its electrical conductivity. Therefore, if the electrical conductivity of the muscle could be measured, the degree of muscle fatigue could be evaluated. However, if sweating occurs simultaneously with muscle movement, the electrical conductivity of the skin changes significantly. When measuring the impedance of the entire cross section of a living body's arm, there are two variable factors, the amount of blood in the muscle and the amount of sweating, so it is not possible to measure only the impedance of the muscle, and therefore it is not possible to correctly evaluate the amount of blood in the muscle.

[0035] Therefore, in the first embodiment, the impedance inside the living body is measured as follows: A current I1 is applied to the living body via the second electrode 11 by the first current source 13, and the current value and voltage value at this time are measured by the first ammeter 15 and the voltmeter 17. Then, the voltage value is divided by the current value to calculate the impedance Zout.

[0036] Meanwhile, a current I2 is applied to the living body via the third electrode 12 by the second current source 14, and the current value and voltage value at this time are measured by the second ammeter 16 and voltmeter 17. Then, the voltage value is divided by the current value to calculate the impedance Zall.

[0037] The third electrode 12 is widely spaced, and the second electrode 11 is disposed inside the third electrode 12, with the distance between the electrodes being short. Therefore, the current I2 is distributed from the surface to the inside of the living body, whereas the current I1 is distributed biased toward the surface of the living body. Therefore, the impedance Zout can be approximated to the impedance of the surface of the living body, and the impedance Zall can be approximated to the impedance of the entire cross section of the living body.

[0038] Figure 15 shows the current distribution inside a living body obtained by electromagnetic field simulation. Figure 15(a) shows the distribution of current I2, and Figure 15(b) shows the distribution of current I1. The living body model is as shown in Figure 2, with the bone outer diameter of 20 mm, muscle thickness of 30 mm, fat thickness of 7 mm, and skin thickness of 3 mm, and I1 and I2 are set to 500 Hz. The electrical conductivity is 0.34 S / m for skin, 0.4327 S / m for fat, 0.351828 S / m for muscle, and 0.02064 S / m for bone. As shown in Figure 15, it can be seen that current I2 is distributed deep inside the living body, while current I1 is concentrated on the surface of the living body.

[0039] Here, as shown in Fig. 3, the impedance Zall of the entire cross section of the living body can be approximated to the parallel impedance of the impedance Zout of the surface of the living body and the impedance Zin inside the living body. Therefore, if Zout and Zall are obtained, Zin can be calculated by Zin = Zout x Zall / (Zout - Zall). In this way, the calculation unit 18 calculates the impedance Zin inside the living body from the measured values ​​of the first ammeter 15, the second ammeter 16, and the voltmeter 17. Since the impedance Zin inside the living body can be approximated to the impedance of a muscle, it can be used for various muscle-related evaluations, such as the degree of muscle fatigue.

[0040] As described above, according to the first embodiment, it is possible to measure impedance inside a living body with a simple configuration.

[0041] Next, a more detailed model of the living body and muscle fatigue measurement will be described.

[0042] Generally, bioelectrical impedance is treated as a complex impedance. Figure 8 shows the flow of current in a living body. As shown in Figure 8, the cell membrane has capacitance, and at low frequencies, current flows through the external fluid, bypassing the cells. On the other hand, at high frequencies, current flows not only through the external fluid but also through the internal fluid within the cells. Figure 9 shows the equivalent circuit of the living body. As shown in Figure 9, the resistance of the extracellular fluid is Re, the resistance of the intracellular fluid is Ri, and the capacitance of the cell membrane is Cm, and it is expressed by a series connection of Cm and Ri and a parallel connection with Re. At low frequencies, current flows on the Re side as shown in Figure 9(a), and at high frequencies, it flows on both sides as shown in Figure 9(b). Figure 10 shows a Cole-Cole plot of bioelectrical impedance Z. Theoretically, the lower the frequency, the closer it is to Re, and the higher the frequency, the closer it is to Re / / Ri (the parallel resistance of Re and Ri).

[0043] When a muscle becomes fatigued, blood flows into the muscle. Since the conductivity of blood is higher than that of muscle, muscle fatigue reduces bioelectrical impedance Z. Figure 11 shows bioelectrical impedance Z before and after muscle fatigue. As shown in Figure 11, the real part of Z decreases due to muscle fatigue, so the degree of muscle fatigue can be evaluated by evaluating the amount of change by measuring the impedance inside the body as described above.

[0044] However, the real part of Z varies from person to person, and it may be difficult to evaluate muscle fatigue only by the change in the real part of Z. Therefore, by using the change in the intracellular / extracellular fluid resistance ratio Re / Ri or the change in the impedance ratio inside the living body at different frequencies as an evaluation index, it is possible to reduce errors due to individual differences and measure muscle fatigue more accurately. The impedance ratio inside the living body at different frequencies is, for example, the ratio of the impedance inside the living body at a low frequency to the impedance inside the living body at a high frequency. The low frequency is, for example, 100Hz to 10kHz, and the high frequency is, for example, 100kHz to 10MHz.

[0045] Figure 12 shows an equivalent circuit of a living body that takes complex impedance into account. In the case of such a circuit, the impedance inside the living body can be measured by Zin = Zout x Zall / (Zout - Zall). Figure 13 shows an example of calculating Zall, Zin, and Zout. It can be confirmed that the impedance Zin inside the living body can be calculated even when complex impedance is taken into account.

[0046] Next, the preferable range for the interval between each electrode will be described. The wider the interval between the electrodes through which current flows, the deeper the current can flow. However, the thickness of the living body varies depending on the part. Therefore, assuming the thickness of the part of the living body where the internal impedance is to be measured as D1 and the interval between the third electrodes 12 as L1, it is preferable that 0.1 ≦ L1 / D1 ≦ 5. By making L1 approximately the same as D1, while miniaturizing the device, the current can be made to flow deep inside. Also, the current flowing through the second electrode 11 needs to be localized in the skin part of the living body. Therefore, assuming the skin thickness of the part of the living body where the internal impedance is to be measured as D2 and the interval between the second electrodes 11 as L2, it is preferable that 0.1 ≦ L2 / D2 ≦ 5. By making L2 approximately the same as D2, the current is localized in the skin part of the living body. Note that, due to the arrangement of the electrodes, assuming the interval between the first electrodes 10 as L3, L3 < L2 < L1 is satisfied. The interval L3 of the first electrodes 10 may be arbitrarily set within the range satisfying 0 < L3 < L2.

[0047] FIG. 14 is a diagram showing the configuration of a muscle fatigue degree measuring device using the living body electrical impedance measuring device of the first embodiment. As shown in FIG. 14, the muscle fatigue degree measuring device is a band-aid type device, and an adhesive is applied to one surface (the back surface) of an insulator sheet 21. Also, on the back surface of the insulator sheet 21, the first electrode 10, the second electrode 11, and the third electrode 12 are arranged in the same manner as in the first embodiment. Further, on the front surface of the sheet 21, a device integrating the first current source 13, the second current source 14, the first ammeter 15, the second ammeter 16, the voltmeter 17, the calculation unit 18, and the display unit 20 is mounted. The back surface of the sheet 21 is attached to the living body, the first electrode 10, the second electrode 11, and the third electrode 12 are brought into contact with the living body, and the internal impedance of the living body is measured in the same manner as in the first embodiment. The calculation unit 18 estimates the muscle fatigue degree from the calculated change in the internal impedance of the living body. The display unit 20 displays the estimated fatigue degree in characters or the like. For example, the fatigue degree is determined in three stages: low, medium, and high, and "Fatigue degree: high" or the like is displayed.

[0048] Instead of or in addition to the display by the display unit 20, the fatigue level may be notified by an alarm or a sound. Also, instead of or in addition to the display unit 20, a wireless communication device such as Bluetooth (registered trademark) may be provided. The information on the muscle fatigue level calculated by the calculation unit 18 is transmitted by the wireless communication device and received by a wireless communication terminal such as a smartphone or tablet terminal, and the muscle fatigue level can be displayed on the wireless communication terminal or notified by sound. In this case, the calculation unit 18 may be an application installed in the wireless communication terminal.

[0049] (Variation 1) As shown in FIG. 4, the shape of the second electrode 11 may be a circular arc convex toward the first electrode 10. It does not have to be a circular arc as long as it is a linear shape extending perpendicular to the straight line connecting the first electrodes 10. By using such an electrode shape, the current distribution on the surface of the living body when a current is passed through the second electrode 11 is equivalent to the current distribution on the surface of the living body when a current is passed through the third electrode 12, and the impedance inside the living body can be obtained with higher accuracy. As shown in FIG. 5, the length of the second electrode 11 (the length perpendicular to the straight line connecting the first electrodes 10) is x, the distance between the third electrodes 12 is L1, and the distance between the second electrodes 11 is L2, and x is set within a range of 0.8≦(2(L1−L2)). 1 / 2 It is preferable that the value is ≦1.2. Within this range, the current distribution on the surface of the living body when a current is applied via the second electrode 11 and the current distribution on the surface of the living body when a current is applied via the third electrode 12 can be made more equivalent.

[0050] (Variation 2) As shown in Fig. 5, the current source may be only the first current source 13, and a pair of switches 19 may be provided to switch the connection between the first current source 13 and the second electrode 11 and the third electrode 12. Fig. 5(a) shows a state in which the first current source 13 and the third electrode 12 are connected. Fig. 5(b) shows a state in which the first current source 13 and the second electrode 11 are connected. With this configuration, only one current source and one ammeter are required, which allows for a smaller device and lower costs.

[0051] (Modification Example 3) In the above-described first embodiment, the current I1 from the first current source 13 and the current I2 from the second current source 14 were alternately passed. However, as shown in FIG. 6, the current I1 from the first current source 13 and the current I2 from the second current source 14 may be passed simultaneously with opposite phases. In this case, the current distribution in the biological cross-section is as shown in FIG. 7. As shown in FIG. 7, the current I1 flowing through the living body from the first current source 13 via the second electrode 11 is distributed on the surface of the living body. On the other hand, the current I2 flowing through the living body from the second current source 14 via the third electrode 12 is distributed not only on the surface of the living body but also inside. Here, the current I1 and the current I2 are in opposite phases. Therefore, the currents cancel each other out on the surface of the living body, and the current is mainly distributed inside the living body. By measuring this current value with the second ammeter 16 and measuring the voltage with the voltmeter 17, the impedance inside the living body can be calculated. In short, the first embodiment is configured to remove the surface impedance by calculation processing, while the modification example 3 is configured to physically remove the surface impedance.

[0052] When the currents I1 and I2 are passed simultaneously with opposite phases as in Modification Example 3, the amplitudes of the currents I1 and I2 are set such that I1 = k×I2, where 0.1×(L2 / L1) 2 <k<(L2 / L1) 2 It is preferable to set it in this way. By setting k in this manner, with the current density of current I1 being I1' and the current density of current I2 being I2', it is possible to make I1'<I2' in any region. In particular, the current can be largely canceled on the surface of the living body, and the current density can be increased inside the living body. As a result, the influence of impedance fluctuations on the surface of the living body can be further reduced, and the measurement sensitivity of impedance fluctuations inside the living body can be enhanced.

Industrial Applicability

[0053] The present invention can be used for measuring the degree of muscle fatigue and the like.

Explanation of Reference Numerals

[0054] 10: First Electrode 11: Second Electrode 12: Third Electrode 13: 1st current source 14:Second current source 15: 1st ammeter 16:Second ammeter 17:Voltmeter 18: Calculation section 19: Switch 20: Display section 21: Sheet

Claims

1. A pair of first electrodes to be brought into contact with a living body; A pair of electrodes to be brought into contact with the living body, the second electrodes being spaced apart on a straight line connecting the pair of first electrodes, and arranged so that the pair of first electrodes are on the inside; A pair of electrodes to be brought into contact with the living body, the third electrode being disposed on a straight line connecting the pair of first electrodes and spaced apart from each other, and the pair of second electrodes being disposed on the inner side; a measurement unit that flows a first current through the surface of the living body via the second electrode and simultaneously flows a second current having a phase opposite to that of the first current through the surface and inside of the living body via the third electrode so that the first current and the second current cancel each other out on the surface of the living body, and in this state measures a current value of the second current and a voltage value between the first electrodes to calculate an impedance inside the living body; A bioelectrical impedance measuring device comprising:

2. 2. The bioelectrical impedance measuring device according to claim 1, wherein the second electrode has a linear shape extending in a direction perpendicular to a straight line connecting the pair of the first electrodes.

3. A bioelectrical impedance measuring device as described in claim 1 or 2, characterized in that the thickness of the part of the body where internal impedance is to be measured is D1, the distance between the third electrodes is L1, and 0.1≦L1 / D1≦5 is satisfied.

4. A bioelectrical impedance measuring device as described in any one of claims 1 to 3, characterized in that the thickness of the skin of the part of the body where the internal impedance is to be measured is D2, the distance between the second electrodes is L2, and 0.1≦L2 / D2≦5 is satisfied.

5. 5. The bioelectrical impedance measuring device according to claim 1, wherein the measuring section evaluates a degree of muscle fatigue from a change in impedance inside the living body.

6. 6. The bioelectrical impedance measuring device according to claim 1, wherein the measuring unit measures the impedance inside the living body at different frequencies and evaluates the degree of muscle fatigue based on a change in the ratio of the impedances.

7. A pair of first electrodes, a second electrode that is a pair of electrodes arranged spaced apart on a straight line connecting the pair of first electrodes and arranged so that the pair of first electrodes is on the inside, and a third electrode that is a pair of electrodes arranged spaced apart on a straight line connecting the pair of first electrodes and arranged so that the pair of second electrodes is on the inside are brought into contact with a living body; a first current is passed through the surface of the living body via the second electrode, and at the same time, a second current having a phase opposite to that of the first current is passed through the surface and inside of the living body via the third electrode, so that the first current and the second current cancel each other out on the surface of the living body, and in this state, a current value of the second current is measured, and a voltage value between the first electrodes is measured to calculate an impedance inside the living body; A method for measuring bioelectrical impedance.

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