Electrical stimulation system

Abstract

To provide an electrical stimulation system that can set a preferable electrical stimulation strength.SOLUTION: An electrical stimulation system includes: a stimulating electrode for imparting an electrical stimulation to user's muscle; measuring electrodes for a plurality of measuring electrodes that measure user's impedance; and a differential value calculation part 52 for calculating a differential value relating to an electrical signal of a relationship between an electrical signal applied to the stimulating electrode and electrical property information on the basis of the measured impedance.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an electrical stimulation system.

Background Art

[0002] Patent Document 1 discloses an electrical stimulation device that applies electrical stimulation to a user's muscles. This electrical stimulation device contracts the muscles by passing a weak current through the muscles to tense and relax them. Thereby, for example, muscle strengthening is achieved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For a user of an electrical stimulation device, it is difficult to determine a suitable electrical stimulation intensity. For example, when aiming for muscle enhancement, should the highest intensity of electrical stimulation within the bearable range be applied, or would an electrical stimulation of a lower intensity also be sufficient? If an electrical stimulation of a lower intensity is sufficient, what intensity of electrical stimulation should be applied? The user cannot make a judgment.

[0005] The present invention has been made in such a situation, and an exemplary object of one aspect thereof is to provide an electrical stimulation system capable of determining a suitable electrical stimulation intensity.

Means for Solving the Problems

[0006] To solve the above problems, an electrical stimulation system according to an aspect of the present invention includes a stimulating electrode for applying electrical stimulation to a user's muscle, a measuring electrode of a plurality of measuring electrodes for measuring the impedance of the user, and a calculating unit that calculates a differential value related to an electrical signal based on the relationship between the electrical signal applied to the stimulating electrode and the electrical characteristic information based on the measured impedance.

[0007] In addition, any combination of the above components, or those obtained by mutually replacing the components and expressions of the present invention among methods, devices, systems, etc., are also effective as aspects of the present invention.

Advantages of the Invention

[0008] According to the present invention, a suitable electrical stimulation intensity can be determined.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 5

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Figure 10

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments. The embodiments are illustrative rather than limiting the invention, and not all features and combinations thereof described in the embodiments are necessarily essential to the invention. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate.

[0011] Before specifically describing the present invention, an overview will be given.

[0012] When the muscle fibers contract, due to mechanical and chemical factors, the current density (the amount of charge flowing per unit time and unit cross-sectional area) applied from the outside increases. That is, (1) as a mechanical factor, the arteries or veins existing inside the muscle also undergo a contraction movement, a kind of pumping effect appears, the blood flow rate (the mass of blood flowing per unit time and unit cross-sectional area) locally increases, and seemingly, the conductivity inside the artery or vein also increases, resulting in an increase in the current density of the muscle. On the other hand, as a chemical factor, (2) this contraction movement of the muscle fibers is anaerobic metabolism, generating a large amount of lactic acid and phenomena such as the generation of hydrogen ions (H+) by the hydrolysis of adenosine triphosphate (ATP), resulting in an increase in the current density of the muscle. That is, when the muscle moves, the conductivity of the muscle locally increases.

[0013] Based on this finding, the inventors of the present invention conceived of the electrical stimulation system of this embodiment. An embodiment of the present invention relates to an electrical stimulation system for applying electrical stimulation to a user's muscles, and more particularly to an electrical stimulation system having a function of determining a suitable electrical stimulation intensity to be applied to the user's muscles, in other words, a function of determining a suitable electrical signal (voltage or current) to be applied to the stimulating electrodes. For this determination, the electrical stimulation system sequentially applies various electrical signals to the stimulating electrodes to apply electrical stimulation to the user's muscles, and measures the impedance of the user. The electrical stimulation system calculates a second-order derivative value of the electrical signal with respect to the relationship between the electrical signal applied to the stimulating electrodes and the electrical specific information (for example, conductivity) based on the impedance measured when each electrical signal is applied. The electrical stimulation system determines a suitable electrical signal to be applied to the stimulating electrodes during training based on the electrical signal at which the second-order derivative value is maximized.

[0014] Hereinafter, embodiments of the present invention will be specifically described. In the following, the case where the electrical stimulation device applies a voltage to the stimulating electrodes will be described as an example, but the present invention is not limited to this, and the electrical stimulation device may apply a current to the stimulating electrodes.

[0015] FIG. 1 is a schematic diagram showing an electrical stimulation system 100 according to an embodiment. The electrical stimulation system 100 includes an electrical stimulation device 10 and a terminal 12. The electrical stimulation device 10 is worn on a body part such as the user's arm, leg, or abdomen. Hereinafter, the body part on which the electrical stimulation device 10 is worn will be referred to as the worn part. The electrical stimulation device 10 applies electrical stimulation to the muscles of the worn part. The electrical stimulation device 10 also measures the impedance of the worn part and transmits the obtained impedance data to the terminal 12.

[0016] The terminal 12 is various information processing terminals including a display unit 48. The terminal 12 may be, for example, a smartphone or a tablet terminal. The terminal 12 is connected to the electrical stimulation device 10 by wire or wirelessly. The terminal 12 controls the electrical stimulation device 10 according to the user's operation.

[0017] Fig. 2 is a rear view of the electrical stimulation device 10. Fig. 3 is a diagram showing a state in which the electrical stimulation device 10 is attached to a receiving part. In many cases, the receiving part on which the electrical stimulation device 10 is attached can be considered to be cylindrical.

[0018] The electrical stimulation device 10 includes a base material 14, a first stimulating electrode 16 and a second stimulating electrode 18 for applying electrical stimulation to the muscle of the applied part, measuring electrodes 20_1 to 20_16 for measuring the impedance of the applied part, collectively referred to as measuring electrodes 20, and a control unit 22. The number of the stimulating electrodes is not limited to two as long as it is more than one. The number of the measuring electrodes 20 is not limited to 16 as long as it is more than one.

[0019] The base material 14 is a member that is attached to the part to be attached, and is in the form of a flat sheet when unfolded. The first stimulating electrode 16 and the second stimulating electrode 18 are provided on a back surface 14a of the base material 14. The first stimulating electrode 16 and the second stimulating electrode 18 have a substantially rectangular shape that extends in the X direction around the periphery of the part to be attached, and are spaced apart from each other in the Y direction perpendicular to the X direction. The first stimulating electrode 16 and the second stimulating electrode 18 are each electrically connected to a control unit 22 by 24 provided on the back surface 14a of the base material 14.

[0020] The multiple measurement electrodes 20 are provided on the back surface 14a of the base material 14. The multiple measurement electrodes 20 are provided so as to be able to measure the impedance of the muscle electrically stimulated by the first and second stimulating electrodes 16, 18. At least one of the multiple measurement electrodes 20 (six in this example) is located between the first stimulating electrode 16 and the second stimulating electrode 18. The multiple measurement electrodes 20 are arranged in a line at equal intervals in the X direction and surround the attachment part. Each of the multiple measurement electrodes 20 is electrically connected to the control unit 22 by wiring 26 provided on the back surface 14a of the base material 14.

[0021] The wirings 24 and 26 are coated with an insulating film so as not to contact the mounted part. The wirings 24 and 26 may be embedded in the base material 14. In this case, if the base material 14 is an insulator, it may not be necessary to coat the wirings 24 and 26 with an insulating film.

[0022] The control unit 22 is an electronic unit and is held in the base material 14. The control unit 22 controls the application of the voltage for muscle stimulation to the first and second stimulating electrodes 16 and 18. The electrical stimulation device 10 can select 20 electrical stimulation intensities from 1 to 20, although not particularly limited. In other words, the electrical stimulation device 10 can select 20 voltage levels from 1 to 20 for the voltage for muscle stimulation applied to the first and second stimulating electrodes 16 and 18. The voltage value for muscle stimulation is a linear function of the voltage level, and the higher the voltage level, the higher the voltage value for muscle stimulation. Further, the control unit 22 controls the measurement of impedance by the plurality of measurement electrodes 20.

[0023] FIG. 4 is a block diagram showing the functional configuration of the electrical stimulation device 10. Each block of the control unit shown in FIG. 4 is realized as elements and circuits including a computer CPU (Central Processing Unit) and memory as a hardware configuration, and is realized by a computer program or the like as a software configuration. Here, however, functional blocks realized by their cooperation are depicted. Therefore, it is understood by those skilled in the art who have read this specification that these functional blocks can be realized in various forms by a combination of hardware and software. The same applies to each block in FIG. 5.

[0024] The control unit 22 includes a power supply unit 30, an electrical stimulation control unit 32, a measurement control unit 34, and a communication unit 36. The power supply unit 30 is a secondary battery such as a lithium ion battery, but may be a replaceable primary battery. The power supply unit 30 is electrically connected to the electrical stimulation control unit 32 and the communication unit 36 and supplies power to them. Note that a power button may be provided on the control unit 22, and the power supply unit 30 may be turned on / off according to the operation of the power button.

[0025] The communication unit 36 transmits and receives information to and from the communication unit 46 (described later) of the terminal 12. The communication unit 36 may transmit and receive information by wireless communication, such as short-range wireless communication like Bluetooth (registered trademark).

[0026] The electrical stimulation control unit 32 controls the application of voltage to the first and second stimulation electrodes 16 and 18 according to the control instruction received from the terminal 12. The electrical stimulation control unit 32 applies a voltage between the first stimulation electrode 16 and the second stimulation electrode 18 at a predetermined frequency (for example, 20 Hz), or stops the application of the voltage. That is, the electrical stimulation control unit 32 applies an electrical stimulation to the worn part or stops the application of the electrical stimulation to the worn part.

[0027] The measurement control unit 34 controls the acquisition of impedance data of the worn part by the plurality of measurement electrodes 20 according to the control instruction received from the terminal 12. For example, the measurement control unit 34 supplies a weak current, such as a current of 1 mA or less that cannot be sensed by the user, between a pair of the plurality of measurement electrodes 20 (for example, between the measurement electrode 20_1 and the measurement electrode 20_2). The measurement control unit 34 measures the potential difference generated between each of the other measurement electrodes 20 (measurement electrodes 20_3 to 20_16) while flowing a weak current through the pair of measurement electrodes 20. By measuring the potential difference while sequentially changing the measurement electrode 20 through which the current flows to the measurement electrode 20_2 and the measurement electrode 20_3, the measurement electrode 20_3 and the measurement electrode 20_4, ···, impedance data in the section of the worn part is acquired. The impedance data here is data including a resistance value (a function of conductivity) and an electrical capacitance (capacitance, a function of permittivity). The measurement control unit 34 transmits the acquired impedance data to the terminal 12.

[0028] Note that impedance data at the moment of applying electrical stimulation may sometimes be buried in the power applied for the electrical stimulation and thus cannot be obtained. Therefore, when the measurement control unit 34 acquires impedance data while applying electrical stimulation of a predetermined frequency, it may acquire the impedance data at a timing that avoids the moment of applying the electrical stimulation, that is, at the timing between electrical stimulations, or it may apply noise processing such as Fourier transform.

[0029] FIG. 5 is a block diagram showing the functional configuration of the terminal 12. The terminal 12 includes an electrical stimulation intensity determination unit 40, a training control unit 42, a display control unit 44, a communication unit 46, and a display unit 48. The display unit 48 is a touch panel type display device such as a liquid crystal panel or an organic EL panel, and displays information on the screen and receives user operation inputs.

[0030] The electrical stimulation intensity determination unit 40 determines a suitable electrical stimulation intensity to be applied to the user's muscles. In other words, the electrical stimulation intensity determination unit 40 determines a suitable voltage level (hereinafter referred to as the suitable voltage level) to be applied to the first and second stimulation electrodes 16 and 18, and thus a suitable voltage value for muscle stimulation (hereinafter referred to as the suitable voltage value).

[0031] The electrical stimulation intensity determination unit 40 includes a conductivity acquisition unit 50, a muscle compartment extraction unit 51, a differential value calculation unit 52, and a suitable voltage determination unit 54.

[0032] The conductivity acquisition unit 50 acquires the conductivity distribution when various voltages are sequentially applied to the first and second stimulation electrodes 16 and 18. Specifically, the conductivity acquisition unit 50 transmits a control instruction to the control unit 22 of the electrical stimulation device 10 to sequentially apply voltages of various voltage levels to the first and second stimulation electrodes 16 and 18 to stimulate the muscles, and measure the impedance of the worn part at that time. When the conductivity acquisition unit 50 receives impedance data from the electrical stimulation device 10 as a response to the control instruction, it reconstructs the conductivity distribution (i.e., tomographic image) of the worn part for each voltage level. The reconstruction by the conductivity acquisition unit 50 may be realized by a known reconstruction method.

[0033] The conductivity acquisition unit 50 may sequentially apply a plurality of voltages up to the voltage level specified by the user. The conductivity acquisition unit 50 may sequentially apply the voltages at all voltage levels up to the voltage level specified by the user, or may sequentially apply them skipping one or more. For example, when sequentially applying the voltages at the voltage levels up to voltage level 14, the voltages at the voltage levels may be sequentially applied skipping one. That is, the voltages at voltage levels 2, 4, 6, 8, 10, 12, 14 may be sequentially applied.

[0034] The control instruction by the conductivity acquisition unit 50 may be, for example, (a) applying a voltage to the first and second stimulating electrodes 16, 18 for 5 minutes to apply an electrical stimulation to the worn part, and after the application of the electrical stimulation is completed, (b) measuring the impedance of the worn part, and after the measurement of the impedance is completed, (c) taking a break for, for example, 10 minutes without applying the electrical stimulation or measuring the impedance, increasing the voltage level, and repeating (a) to (c).

[0035] The muscle compartment extraction unit 51 extracts the conductivity distribution of a specific muscle compartment (hereinafter referred to as the specific muscle compartment) from the conductivity distribution (tomographic image) at each voltage level. The specific muscle compartment may be specified by the user, for example, or may be, for example, the muscle compartment with the highest conductivity. The muscle compartment with the highest conductivity may be the muscle compartment with the highest spatial average value of conductivity, or may be the muscle compartment with the highest maximum value of conductivity.

[0036] For example, when the worn part is the lower leg, the specific muscle compartment is any one of the muscle compartments of the gastrocnemius muscle, tibialis anterior muscle, extensor digitorum longus muscle, peroneus longus muscle, and soleus muscle. For example, when the electrical stimulation device 10 is worn so that the first and second stimulating electrodes 16, 18 contact the back side of the lower leg to apply an electrical stimulation to the gastrocnemius muscle, the gastrocnemius muscle may be specified as the specific muscle compartment. Alternatively, in that case, the gastrocnemius muscle will inevitably be specified as the muscle compartment with the highest conductivity, that is, the specific muscle compartment.

[0037] The differential value calculation unit 52 calculates the second derivative value with respect to the voltage value of the relationship between the applied voltage value and the conductivity for the conductivity distribution at each voltage level of the specific muscle section. Specifically, the differential value calculation unit 52 calculates the second derivative value of the conductivity with respect to the voltage value for each position of the specific muscle section from the conductivity distribution at each voltage level of the specific muscle section. FIG. 6 is a schematic diagram showing an image of the second derivative value of the conductivity with respect to the voltage value. Each tomographic image in FIG. 6 shows the second derivative value of the conductivity of the lower leg. In FIG. 6, the +x direction is the right direction, the +y direction is the front direction, and the φ direction indicates the direction of the voltage value.

[0038] In this embodiment, the differential value calculation unit 52 calculates the second derivative value (second difference value) by difference approximation. Here, central difference is used as the difference approximation, and the second derivative value at each position of the specific muscle section is calculated by the following formula (1). Note that forward difference or backward difference may be used for the difference approximation. [Number] Here, φ: Voltage value Δφ: Difference in voltage values between adjacent voltage levels (step size) σ φ Vector: Conductivity distribution of the specific muscle section when the voltage value φ is applied is. When the voltage levels are sequentially applied skipping n levels, Δφ in formula (1) may be set to nΔφ.

[0039] The suitable voltage determination unit 54 determines the suitable voltage level and thus the suitable voltage. The suitable voltage determination unit 54 determines the suitable voltage level based on the voltage level at which the second derivative value is maximized (hereinafter referred to as the maximum voltage level).

[0040] For example, the maximum voltage level may be the voltage level at which the spatial average of the second derivative value (second difference value) at each position in a specific muscle section is maximized. Also, for example, the maximum voltage level may be the voltage level at the maximum value of an approximate curve obtained by performing curve fitting on the relationship between the second derivative value (second difference value) and the applied voltage at each position in a specific muscle section. Known methods such as the least squares method may be used for curve fitting.

[0041] Also, for example, the maximum voltage level may be the voltage level at which the second derivative value (second difference value) at a representative position in a specific muscle section is maximized. Also, for example, the maximum voltage level may be the voltage level at the maximum value of an approximate curve obtained by performing curve fitting on the relationship between the second derivative value (second difference value) and the applied voltage at a representative position in a specific muscle section.

[0042] For example, the suitable voltage determination unit 54 may determine the maximum voltage level as the suitable voltage level. In this case, the muscle can be trained efficiently. Also, for example, the suitable voltage determination unit 54 may determine the voltage level obtained by multiplying the maximum voltage level by a predetermined safety factor (e.g., 0.8) as the suitable voltage level. In this case, the muscle can be trained moderately.

[0043] Also, for example, the suitable voltage determination unit 54 may determine the voltage level obtained by multiplying the maximum voltage level by a coefficient corresponding to the user's exercise purpose (e.g., muscle strengthening, endurance enhancement, diet, rehabilitation, etc.) or attributes (e.g., age, gender, height, weight, etc.) as the suitable voltage level. For example, the coefficient may increase in the order of exercise purposes of muscle strengthening, endurance enhancement, diet, and rehabilitation. Also, for example, the safety factor for those under 17 years old and over 50 years old may be lower (farther from 1.0) compared to those aged 18 to 49 years old. The exercise purpose and attributes may be input by the user in advance and held in the terminal 12.

[0044] The training control unit 42 controls the electrical stimulation by the control unit 22 of the electrical stimulation device 10 and thus the electrical stimulation device 10 by sending a control instruction regarding the electrical stimulation to the control unit 22. The control instruction is, for example, an instruction to start electrical stimulation including a voltage level or an instruction to end it. The suitable voltage level determined by the suitable voltage determination unit 54 may be set for this voltage level, or it may be set automatically, for example.

[0045] Also, the training control unit 42 controls the acquisition of impedance by the control unit 22 of the electrical stimulation device 10 and thus the electrical stimulation device 10 by sending an instruction to acquire impedance data to the control unit 22. When the training control unit 42 receives impedance data from the electrical stimulation device 10, it reconstructs the conductivity distribution (i.e., tomographic image) of the worn part. The reconstruction by the training control unit 42 may be realized by a known reconstruction method.

[0046] The display control unit 44 controls the display on the display unit 48. For example, the display control unit 44 displays an image (i.e., conductivity second derivative image) showing the second derivative (difference) value of the conductivity at each position on the display unit 48. FIG. 7 is a diagram showing an example of a screen for displaying the conductivity second derivative image. By displaying this screen on the display unit 48, the maximum voltage level can also be specified from the image.

[0047] Also, for example, the display control unit 44 displays the suitable voltage level determined by the suitable voltage value determination unit on the display unit 48. Also, for example, the display control unit 44 displays a tomographic image showing the conductivity distribution of the worn part during training on the display unit 48.

[0048] The above is the basic configuration of the electrical stimulation system 100. Subsequently, its operation will be described. Here, the operation of determining the suitable voltage level will be described.

[0049] After the user wears the electrical stimulation device 10, the user inputs an instruction to start a process for determining a suitable voltage level to the terminal 12. The terminal 12 transmits a control instruction to the electrical stimulation device 10 to sequentially apply voltages of various voltage levels to the first and second stimulation electrodes 16 and 18 to stimulate the muscle and measure the impedance of the worn part at that time. When receiving the control instruction, the electrical stimulation device 10 repeatedly executes the application of electrical stimulation and the measurement of impedance while taking breaks. When the terminal 12 receives impedance data from the electrical stimulation device 10 as a response to the control instruction, the terminal 12 reconstructs the conductivity distribution of the worn part for each level of the applied electrical stimulation intensity. The terminal 12 extracts the conductivity distribution of a specific muscle compartment from the conductivity distribution for each voltage level. The terminal 12 calculates a second-order differential value (second-order difference value) regarding the voltage value of the relationship between the voltage value and the conductivity distribution for the extracted conductivity distribution of the specific muscle compartment. The terminal 12 determines a suitable voltage value based on the voltage value at which the second-order differential value of the conductivity regarding the voltage value is maximized.

[0050] The above is the operation of the electrical stimulation system 100. Next, the effects achieved by the present embodiment will be described.

[0051] Figs. 8(a) to 8(c) are diagrams for explaining the effects of the electrical stimulation system 100 according to the present embodiment. Fig. 8(a) is a graph showing the average value of the conductivity of a specific muscle compartment when voltages of voltage levels 2, 4, 6, 8, 10, 12, and 14 are applied to a certain representative subject by the electrical stimulation device 10, and Figs. 8(b) and 8(c) are graphs showing the first-order differential value and the second-order differential value thereof. Although not particularly limited, in this example, the voltages of voltage levels 2, 4, 6, 8, 10, 12, and 14 are as follows. Voltage level 2: 13.57V Voltage level 4: 16.71V Voltage level 6: 19.85V Voltage level 8: 22.99V Voltage level 10: 26.13V Voltage level 12: 29.27V Voltage level 14: 32.41V

[0052] As a result of intensive research, the inventors have found that the relationship between the voltage for muscle stimulation and the conductivity of the muscle when the voltage is applied generally follows a function obtained by offsetting the sigmoid function in the X-axis direction. That is, it has been found that when the voltage for muscle stimulation is increased, the conductivity of the muscle gradually increases up to a certain voltage, then rapidly increases, and then gradually increases again. This feature can also be seen from FIG. 8(a). When the conductivity follows the function, the voltage at which the second derivative value becomes maximum is always lower than the voltage at which the first derivative value becomes maximum.

[0053] In the verification conducted by the inventors on a large number of subjects, it has been found that some people start to feel some pain due to electrical stimulation from around the voltage at which the first derivative value becomes maximum. Also, as is clear from FIG. 8(b), when the voltage exceeds the voltage at which the first derivative value becomes maximum, the increase in conductivity becomes sluggish even if the voltage is further increased. That is, the increase in the amount of muscle contraction becomes sluggish. Therefore, it can be said that even if a voltage higher than the voltage at which the first derivative value becomes maximum is applied, the training efficiency does not increase despite the increase in pain.

[0054] On the other hand, the voltage at which the second derivative value becomes maximum is always lower than the voltage at which the first derivative value becomes maximum, as described above. Therefore, the voltage at which the second derivative value becomes maximum can be said to be a safer (more comfortable) voltage compared to the voltage at which the first derivative value becomes maximum. Also, in the verification conducted by the inventors on a large number of subjects, almost no one felt pain even when the voltage at which the second derivative value becomes maximum was applied. Also, the voltage at which the second derivative value becomes maximum is not a voltage that is much lower than the voltage at which the first derivative value becomes maximum, and therefore the muscle can be contracted to a certain extent.

[0055] From the above, it can be seen that if the appropriate voltage level is determined based on the voltage at which the second derivative value becomes maximum, that is, the maximum voltage level, the muscle can be trained safely and efficiently.

[0056] Further, according to the present embodiment, the conductivity distribution of a specific muscle compartment is extracted, and a second derivative value is calculated based on the extracted conductivity distribution. As a result, the voltage level can be determined more accurately for the specific muscle compartment.

[0057] As described above, the present invention has been described based on the embodiments. These embodiments are illustrative, and it is understood by those skilled in the art that various modifications are possible for each of these constituent elements and combinations of each processing process, and such modifications are also within the scope of the present invention. Hereinafter, such modifications will be described.

[0058] (Modification 1) Although not particularly mentioned in the embodiment, there is a certain correlation between the fat thickness and the suitable voltage level, and the thicker the fat, the higher the suitable voltage level tends to be. Therefore, in this modification, the fat thickness is specified, and a candidate for the suitable voltage level (hereinafter referred to as a suitable voltage level candidate) is specified from the specified fat thickness. Then, in the acquisition of the conductivity distribution by the conductivity acquisition unit 50, voltages of voltage levels within a predetermined voltage level range based on the suitable voltage level candidate are sequentially applied. Hereinafter, the differences from the embodiment will be mainly described.

[0059] FIG. 9 is a block diagram showing the functional configuration of the terminal 12 according to the modification. The electric stimulation intensity determination unit 40 of this modification includes a conductivity acquisition unit 50, a muscle compartment extraction unit 51, a derivative value calculation unit 52, a suitable voltage determination unit 54, a fat thickness specification unit 56, a candidate determination unit 58, and a correspondence relationship holding unit 60.

[0060] The correspondence relationship holding unit 60 holds correspondence relationship data between the fat thickness of the worn part and the suitable voltage level candidate. FIG. 10 is a diagram showing an example of the correspondence relationship data. In this example, the correspondence relationship data is data associating the range of the fat thickness with the suitable voltage level candidate.

[0061] The correspondence relationship may be created in advance for a large number of users by, for example, using the electrical stimulation system 100 to identify the fat thickness as described below, further identifying the suitable voltage level as described below, and based on the identified data thereof.

[0062] The fat thickness identification unit 56 identifies the fat thickness of the worn part. The fat thickness identification unit 56 transmits a control instruction for instructing the measurement of impedance to the control unit 22 of the electrical stimulation device 10. When the fat thickness identification unit 56 receives impedance data from the electrical stimulation device 10 as a response to the control instruction, it reconstructs the conductivity distribution (tomographic image) of the worn part. The reconstruction by the fat thickness identification unit 56 may be realized by a known reconstruction method. The fat thickness identification unit 56 identifies the conductivity distribution of fat from the conductivity distribution of the worn part, for example, by filtering, based on the differences in conductivity of fat, muscle, and bone. The fat thickness identification unit 56 identifies the fat thickness from the identified conductivity distribution of fat. The fat thickness may be a representative value or a spatial average value.

[0063] The fat thickness may be identified by other methods such as measurement by ultrasonic waves. In this case, the fat thickness identification unit 56 may acquire the fat thickness identified by other methods.

[0064] The candidate determination unit 58 determines a suitable voltage level candidate from the identified fat thickness and the correspondence relationship data held in the correspondence relationship holding unit. For example, when the fat thickness is 2.5 mm, the voltage level 3 is determined as a suitable voltage level candidate.

[0065] The conductivity acquisition unit 50 sequentially applies voltages at voltage levels within a predetermined range based on the suitable voltage level candidate. For example, the predetermined range is a range of voltage levels based on the suitable voltage level candidate. For example, when the suitable voltage level candidate is Lc, it may be a range from Lc - m to Lc + n (both m and n are positive integers), or a range from 1 to Lc + n.

[0066] According to this modification example, since the range of the voltage level at which the conductivity acquisition unit 50 acquires the conductivity distribution is limited, the time required for acquiring the conductivity distribution and thus determining the suitable voltage level can be shortened.

[0067] (Modification Example 2) In the embodiment, the case where the plurality of measurement electrodes 20 are provided to be arranged in a row in the X direction has been described, but it is not limited thereto, and they may be provided to be arranged in a plurality of rows in the X direction. For example, the plurality of measurement electrodes 20 may be arranged in three rows on the side opposite to the second stimulation electrode 18 with respect to the first stimulation electrode 16, between the first stimulation electrode 16 and the second stimulation electrode 18, and on the side opposite to the first stimulation electrode 16 with respect to the second stimulation electrode 18. In this case, conductivity distributions (tomographic images) of a plurality of layers can be obtained.

[0068] For example, the differential value calculation unit 52 calculates the second-order differential value of the conductivity with respect to the voltage value for each position of the specific muscle section from the conductivity distribution of the specific muscle section at each voltage level extracted from each of the conductivity distributions of the plurality of layers. For example, the suitable voltage determination unit 54 determines the suitable voltage level based on the voltage level at which the spatial average of the second-order differential values (second-order difference values) at each position of the specific muscle section of the plurality of layers is maximized.

[0069] (Modification Example 3) In the embodiment, the case where the electrical stimulation device 10 includes only a pair of stimulation electrodes has been described, but it is not limited thereto, and the electrical stimulation device 10 may include a plurality of pairs of stimulation electrodes, and the plurality of pairs of stimulation electrodes may be provided to be arranged in, for example, the X direction. In this case, the voltage level may be determined for each pair of stimulation electrodes, in other words, for each muscle section corresponding to the pair of stimulation electrodes.

[0070] For example, when the worn part is the lower leg and the electrical stimulation device 10 is equipped with two pairs of stimulating electrodes, and the electrical stimulation device 10 is worn such that one pair of stimulating electrodes electrically stimulates the gastrocnemius muscle and the other pair of stimulating electrodes electrically stimulates the soleus muscle, a suitable voltage level may be determined for each muscle compartment of the gastrocnemius muscle and the soleus muscle, that is, for each pair of stimulating electrodes. In this case, each member of the electrical stimulation intensity determination unit 40 may execute its respective process for each muscle compartment, that is, for each pair of stimulating electrodes. For example, first, assuming that the gastrocnemius muscle is a specific muscle compartment, the muscle compartment extraction unit 51, the differential value calculation unit 52, and the suitable voltage determination unit 54 execute their respective processes to determine the suitable voltage level for the gastrocnemius muscle. Next, assuming that the soleus muscle is a specific muscle compartment, the muscle compartment extraction unit 51, the differential value calculation unit 52, and the suitable voltage determination unit 54 execute their respective processes to determine the suitable voltage level for the soleus muscle. That is, for each of the plurality of muscle compartments, a second-order differential value of the conductivity with respect to the voltage value may be calculated, and a suitable voltage level may be determined based on the calculated second-order differential value.

[0071] (Modification Example 4) In the embodiment, the case where the suitable voltage level (suitable voltage value) is determined based on the second derivative value of the conductivity with respect to the voltage value has been described, but the present invention is not limited to this. For example, the suitable voltage level may be determined based on the first derivative value of the conductivity with respect to the voltage value. In this case, the derivative value calculation unit 52 calculates the first derivative value of the conductivity with respect to the voltage value for each position of the specific muscle section from the conductivity distribution of the specific muscle section for each voltage level. Here, when the voltage level is increased, the conductivity increases, and when the voltage level is increased to a certain point, even if the voltage level is further increased, the conductivity does not increase anymore, that is, it is considered that the increase in conductivity stops and settles at a certain value. Therefore, even if the voltage level is further increased, the amount of muscle contraction does not increase so much, only the electrical stimulation becomes stronger and pain is felt. That is, even if the voltage level is further increased, the muscle cannot be trained efficiently and safely. Therefore, in this modification example, the voltage level when the conductivity settles at a certain value is defined as the suitable voltage level. When the conductivity settles at a certain value, the first derivative of the conductivity approaches 0. Therefore, the suitable voltage determination unit 54 determines the voltage level at which the first derivative value of the conductivity with respect to the voltage value is 0 or less than a predetermined value as the suitable voltage level.

[0072] (Modification Example 5) In the embodiment and the above-described modification examples, the case where the conductivity distribution of the worn part is obtained based on the impedance data has been described, but the distribution of the permittivity or phase of the worn part may be reconstructed based on the impedance data. In this case, in the embodiment and the above-described modification examples, the conductivity may be read as "permittivity" or "phase".

[0073] (Modification Example 6) The control unit 22 of the electrical stimulation device 10 may have at least a part of the functions of the electrical stimulation intensity determination unit 40 of the terminal 12 in the embodiment and the above-described modification examples. In this case, the electrical stimulation device 10 may include a display unit for the control unit 22 to notify the user.

[0074] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present invention. The new embodiments generated by the combination have the effects of the respective embodiments and modifications being combined.

[0075] It is also understood by those skilled in the art that the functions to be performed by each constituent element described in the claims are realized by a single one of the constituent elements shown in the embodiments and modifications or by their association.

Explanation of Reference Numerals

[0076] 10 Electrical stimulation device, 12 Terminal, 16 First stimulation electrode, 18 Second stimulation electrode, 20_1 to 20_16 Measurement electrodes, 52 Differential value calculation unit, 100 Electrical stimulation system.

Claims

1. A stimulating electrode for applying an electrical stimulus to a user's muscle, a plurality of measuring electrodes for measuring the impedance of the user, a differential value calculation unit that calculates a differential value of an electrical signal based on electrical characteristic information based on the impedance measured by the plurality of measuring electrodes, the electrical characteristic information being based on an impedance that changes corresponding to the electrical signal applied to the stimulating electrode, An electrical stimulation system comprising:

2. The electrical stimulation system according to claim 1, wherein the differential value is a spatial average value of a predetermined space.

3. The electrical stimulation system according to claim 2, wherein the spatial average value is a spatial average of one muscle compartment.

4. The electrical stimulation system according to any one of claims 1 to 3, wherein the differential value calculation unit calculates the differential value for each of a plurality of muscle compartments.

5. The differential value calculation unit calculates the differential value for each position in a predetermined space, The electrical stimulation system according to claim 1, further comprising a display control unit that causes a distribution image of the differential value in the space to be displayed on a predetermined display unit.

6. The electrical stimulation system according to any one of claims 1 to 5, wherein the differential value calculation unit calculates the differential value by difference approximation.

7. The electrical stimulation system according to any one of claims 1 to 6, wherein the differential value is a second-order differential value.

8. The electrical stimulation system according to claim 7, further comprising a determination unit that determines an electrical signal suitable for the user, which is an electrical signal to be applied to the stimulating electrode, based on the electrical signal among the electrical signals applied to the stimulating electrode, for which the second-order differential value is maximum.

9. The electrical stimulation system according to any one of claims 1 to 8, wherein the electrical characteristic information is conductivity, permittivity, or phase.

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