JP7701698B2 - Electrical Stimulation System - Google Patents

Description

The present invention relates to an electrical stimulation system.

Patent Document 1 discloses an electrical stimulation device that applies electrical stimulation to the muscles of a user. This electrical stimulation device passes a weak current through the muscles, causing them to tense and relax, thereby contracting the muscles. This allows, for example, for muscle strengthening.

JP 2017-6644 A

It is difficult for users of electrical stimulation devices to determine the appropriate electrical stimulation intensity. For example, if the goal is to build muscle, the user cannot decide whether they should apply the highest intensity electrical stimulation that they can tolerate, whether electrical stimulation of a lower intensity is acceptable, and if electrical stimulation of a lower intensity is acceptable, what intensity of electrical stimulation should be applied.

The present invention has been made in light of this situation, and one exemplary objective of one aspect of the present invention is to provide an electrical stimulation system that can determine a suitable electrical stimulation intensity.

To solve the above problems, an electrical stimulation system according to one embodiment of the present invention includes a stimulation electrode for applying electrical stimulation to a user's muscles, a plurality of measurement electrodes for measuring the impedance of the user, and a calculation unit for calculating a differential value of an electrical signal that is related to an electrical signal applied to the stimulation electrode and electrical characteristic information based on the measured impedance.

In addition, any combination of the above components, or mutual substitution of the components or expressions of the present invention between methods, devices, systems, etc., are also valid aspects of the present invention.

The present invention allows the appropriate electrical stimulation intensity to be determined.

1 is a schematic diagram showing an electrical stimulation system according to an embodiment; FIG. 2 is a rear view of the electrical stimulation device of FIG. 1 . 2 is a diagram showing a state in which the electrical stimulation device of FIG. 1 is attached to a receiving part. FIG. 2 is a block diagram showing a functional configuration of the electrical stimulation device of FIG. 1. FIG. 2 is a block diagram showing a functional configuration of the terminal shown in FIG. 1 . FIG. 2 is a schematic diagram showing an image of a second derivative value of conductivity with respect to a voltage value. FIG. 13 is a diagram showing an example of a screen displaying a second derivative image of electrical conductivity. 2 is a diagram for explaining the effect of the electrical stimulation system of FIG. 1 . FIG. 13 is a block diagram showing a functional configuration of a terminal according to a modified example. 10 is a diagram showing an example of correspondence data stored in a correspondence storage unit shown in FIG. 9 .

The present invention will be described below based on preferred embodiments with reference to the drawings. The embodiments are illustrative and do not limit the invention, and all features and combinations described in the embodiments are not necessarily essential to the invention. The same reference numerals are used to denote identical or equivalent components, parts, and processes shown in each drawing, and duplicate descriptions will be omitted as appropriate.

Before describing the invention in detail, let us provide an overview.

When muscle fibers contract, the current density (amount of charge flowing per unit time and unit cross-sectional area) increases when a current is applied from the outside due to mechanical and chemical factors. That is, (1) as a mechanical factor, the arteries or veins inside the muscle also contract, causing a kind of pump effect, locally increasing the amount of blood flowing (mass of blood flowing per unit time and unit cross-sectional area), and the electrical conductivity inside the arteries or veins also increases, resulting in an increase in the current density of the muscle. On the other hand, as a chemical factor, (2) the contraction of the muscle fibers is an anaerobic metabolism, producing large amounts of lactic acid, and phenomena such as the generation of hydrogen ions (H+) through the hydrolysis of adenosine triphosphate (ATP) occur, resulting in an increase in the current density of the muscle. In other words, when muscles exercise, the electrical conductivity of the muscle increases locally.

Based on this knowledge, the inventors have come up with the electrical stimulation system of the present embodiment. The embodiment of the present invention relates to an electrical stimulation system for applying electrical stimulation to a user's muscles, and in particular 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 stimulation electrodes. For this determination, the electrical stimulation system sequentially applies various electrical signals to the stimulation 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 differential value of the electrical signal, which is a relationship between the electrical signal applied to the stimulation electrodes and electrical specific information (e.g., 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 stimulation electrodes during training based on the electrical signal with the maximum second-order differential value.

The following is a detailed description of an embodiment of the present invention. Note that, although the following description is given taking as an example a case in which the electrical stimulation device applies a voltage to the stimulation electrodes, the present invention is not limited to this, and the electrical stimulation device may also apply a current to the stimulation electrodes.

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 attached to a body part of a user, such as an arm, a leg, or an abdomen. Hereinafter, the body part to which the electrical stimulation device 10 is attached is referred to as the attached part. The electrical stimulation device 10 applies electrical stimulation to the muscles of the attached part. The electrical stimulation device 10 also measures the impedance of the attached part and transmits the obtained impedance data to the terminal 12.

The terminal 12 is an information processing terminal having 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 in response to a user's operation.

Figure 2 is a rear view of the electrical stimulation device 10. Figure 3 is a diagram showing the electrical stimulation device 10 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.

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 muscles of the worn part, measuring electrodes 20_1 to 20_16 for measuring the impedance of the worn part, collectively referred to as measuring electrodes 20, and a control unit 22. The number of stimulating electrodes may be any number greater than one, and is not limited to two. The number of measuring electrodes 20 may be any number greater than one, and is not limited to 16.

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 the back surface 14a of the base material 14. The first stimulating electrode 16 and the second stimulating electrode 18 have a generally 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 the control unit 22 by 24 provided on the back surface 14a of the base material 14.

The multiple measurement electrodes 20 are provided on the back surface 14a of the substrate 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 row 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 substrate 14.

The wires 24, 26 are coated with an insulating film so that they do not come into contact with the mounting portion. The wires 24, 26 may be embedded in the substrate 14. In this case, if the substrate 14 is an insulator, the wires 24, 26 do not need to be coated with an insulating film.

The control unit 22 is an electronic unit and is held within the substrate 14. The control unit 22 controls the application of a muscle stimulation voltage to the first and second stimulation electrodes 16, 18. The electrical stimulation device 10 can select, but is not limited to, 20 electrical stimulation intensities from 1 to 20. In other words, the electrical stimulation device 10 can select 20 voltage levels from 1 to 20 for the muscle stimulation voltage to be applied to the first and second stimulation electrodes 16, 18. The muscle stimulation voltage value is a linear function of the voltage level, and the higher the voltage level, the higher the muscle stimulation voltage value. The control unit 22 also controls the measurement of impedance using the multiple measurement electrodes 20.

Figure 4 is a block diagram showing the functional configuration of the electrical stimulation device 10. Each block of the control unit shown in Figure 4 is realized as a hardware configuration by elements and circuits such as a computer's CPU (Central Processing Unit) and memory, and as a software configuration by a computer program, etc., but here, the functional blocks realized by the cooperation of these are depicted. Therefore, those skilled in the art who have read this specification will understand that these functional blocks can be realized in various ways by combining hardware and software. The same applies to each block in Figure 5.

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

The communication unit 36 transmits and receives information to and from a communication unit 46 (described later) of the terminal 12. The communication unit 36 may transmit and receive information via wireless communication, for example, short-range wireless communication such as Bluetooth (registered trademark).

The electrical stimulation control unit 32 controls the application of voltage to the first and second stimulation electrodes 16, 18 in response to control instructions 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 (e.g., 20 Hz) or stops the application of the voltage. That is, the electrical stimulation control unit 32 applies electrical stimulation to the worn part or stops the application of electrical stimulation to the worn part.

The measurement control unit 34 controls the acquisition of impedance data of the attached part by the multiple measurement electrodes 20 in response to a control instruction received from the terminal 12. For example, the measurement control unit 34 supplies a weak current, for example, a current of 1 mA or less that the user cannot sense, to a pair of the measurement electrodes 20 (for example, between the measurement electrodes 20_1 and 20_2) among the multiple measurement electrodes 20. 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 passing a weak current through the pair of measurement electrodes 20. The measurement control unit 34 obtains impedance data in the layer of the attached part by measuring the potential difference while sequentially changing the measurement electrodes 20 through which the current flows, from the measurement electrodes 20_2 and 20_3, to the measurement electrodes 20_3 and 20_4, .... The impedance data here is data including a resistance value (a function of conductivity) and an electric capacity (capacitance, a function of dielectric constant). The measurement control unit 34 transmits the acquired impedance data to the terminal 12.

In some cases, impedance data at the moment electrical stimulation is applied cannot be obtained because it is buried in the power applied for electrical stimulation. Therefore, when the measurement control unit 34 obtains impedance data while electrical stimulation of a predetermined frequency is being applied, it can obtain the impedance data at a timing that avoids the moment electrical stimulation is applied, that is, at a timing between electrical stimulations, or it can apply noise processing such as Fourier transform.

Figure 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 display device such as a liquid crystal panel or an organic EL panel, and displays information on the screen and accepts user input.

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

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

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

The conductivity acquisition unit 50 may sequentially apply multiple voltages up to a voltage level specified by the user. The conductivity acquisition unit 50 may sequentially apply voltages of all voltage levels up to the voltage level specified by the user, or may sequentially apply voltages skipping one or more voltage levels. For example, when sequentially applying voltages up to voltage level 14, the voltage levels may be sequentially applied skipping one voltage level. In other words, voltage levels 2, 4, 6, 8, 10, 12, and 14 may be sequentially applied.

The control instruction by the conductivity acquisition unit 50 may be, for example, an instruction to (a) apply a voltage to the first and second stimulating electrodes 16, 18 for 5 minutes to provide electrical stimulation to the attached part, and when the application of electrical stimulation is completed, (b) measure the impedance of the attached part, and when the impedance measurement is completed, (c) take a break for, for example, 10 minutes without providing electrical stimulation or measuring impedance, and then increase the voltage level and repeat (a) to (c).

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

For example, when the part to be fitted is the lower leg, the specific compartment is any one of the compartments of the gastrocnemius, tibialis anterior, extensor digitorum longus, peroneus longus, and soleus. For example, when the electrical stimulation device 10 is fitted so that the first and second stimulating electrodes 16, 18 contact the rear side of the lower leg in order to apply electrical stimulation to the gastrocnemius, the gastrocnemius can be specified as the specific compartment. Alternatively, in this case, the gastrocnemius is necessarily specified as the compartment with the highest electrical conductivity, i.e., the specific compartment.

The differential value calculation unit 52 calculates the second-order differential 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 compartment. In detail, 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 compartment from the conductivity distribution at each voltage level of the specific muscle compartment. Figure 6 is a schematic diagram showing an image of the second-order differential value of the conductivity with respect to the voltage value. Each tomographic image in Figure 6 shows the second-order differential value of the conductivity of the lower leg. In Figure 6, the +x direction indicates the right direction, the +y direction indicates the forward direction, and the φ direction indicates the direction of the voltage value.

ここで、
φ：電圧値
Δφ：隣接する電圧レベル同士の電圧値の差（ステップサイズ）
σ^φベクトル：電圧値φを印加したときの特定筋区画の導電率分布
である。
なお、電圧レベルをｎ個飛ばしで順次印加する場合は、式（１）のΔφをｎΔφとすればよい。 In this embodiment, the differential value calculation unit 52 calculates the second-order differential value (second-order difference value) by difference approximation. Here, a central difference is used as the difference approximation, and the second-order differential value at each position of the specific compartment is calculated by the following formula (1). Note that a forward difference or a backward difference may be used for the difference approximation.

Where:
φ: Voltage value Δφ: Difference in voltage value between adjacent voltage levels (step size)
^σφ vector: Electrical conductivity distribution of a specific muscle compartment when a voltage value φ is applied.
When voltage levels are applied in sequence, every nth level, Δφ in equation (1) should be set to nΔφ.

The preferred voltage determination unit 54 determines the preferred voltage level and therefore the preferred voltage. The preferred voltage determination unit 54 determines the preferred voltage level based on the voltage level at which the second differential value is maximum (hereinafter referred to as the maximum voltage level).

For example, the maximum voltage level may be the voltage level at which the spatial average of the second derivative (second difference value) at each position of the specific muscle compartment is maximized. Alternatively, the maximum voltage level may be the voltage level at the maximum value of an approximation curve obtained by performing curve fitting on the relationship between the second derivative (second difference value) at each position of the specific muscle compartment and the applied voltage. A known method such as the least squares method may be used for the curve fitting.

For example, the maximum voltage level may be a voltage level at which the second derivative (second difference value) at a representative position of a specific muscle compartment is maximum.For example, the maximum voltage level may be a voltage level at the maximum value of an approximation curve obtained by performing curve fitting on the relationship between the second derivative (second difference value) at a representative position of a specific muscle compartment and the applied voltage.

For example, the preferred voltage determination unit 54 may determine the maximum voltage level as the preferred voltage level. In this case, the muscles can be trained efficiently. In addition, for example, the preferred 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 preferred voltage level. In this case, the muscles can be trained appropriately.

For example, the preferred voltage determination unit 54 may determine the preferred voltage level as the voltage level obtained by multiplying the maximum voltage level by a coefficient according to the user's exercise purpose (e.g., muscle building, endurance improvement, dieting, rehabilitation, etc.) or attributes (e.g., age, sex, height, weight, etc.). For example, the coefficients may be larger for the exercise purposes of muscle building, endurance improvement, dieting, and rehabilitation in that order. Also, for example, the safety factor may be lower (further from 1.0) for those aged 17 or younger and those aged 50 or older than 18 to 49 years old. The exercise purpose and attributes may be input in advance by the user and stored in the terminal 12.

The training control unit 42 controls the control unit 22 and thus the electrical stimulation by the electrical stimulation device 10 by transmitting control instructions regarding the electrical stimulation to the control unit 22 of the electrical stimulation device 10. The control instructions are, for example, instructions to start or end the electrical stimulation including a voltage level. This voltage level may be set to a preferred voltage level determined by the preferred voltage determination unit 54, or may be set automatically, for example.

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

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

For example, the display control unit 44 displays the preferred voltage level determined by the preferred voltage value determination unit on the display unit 48. For example, the display control unit 44 displays a tomographic image showing the conductivity distribution of the attachment part during training on the display unit 48.

The above is the basic configuration of the electrical stimulation system 100. Next, we will explain its operation. Here, we will explain the operation of determining the preferred voltage level.

After wearing the electrical stimulation device 10, the user inputs an instruction to start processing 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 various voltage levels to the first and second stimulation electrodes 16, 18 to stimulate the muscles and measure the impedance of the attached part at that time. When the electrical stimulation device 10 receives the control instruction, it repeatedly applies electrical stimulation and measures the impedance with breaks in between. When the terminal 12 receives impedance data from the electrical stimulation device 10 in response to the control instruction, it reconstructs the conductivity distribution of the attached 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 the second-order differential value (second-order difference value) of 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 the suitable voltage value based on the voltage value at which the second-order differential value of the conductivity with respect to the voltage value is maximum.

The above is the operation of the electrical stimulation system 100. Next, we will explain the effects of this embodiment.

8(a) to 8(c) are diagrams for explaining the effect of the electrical stimulation system 100 according to the present embodiment. Fig. 8(a) is a graph showing the average conductivity of a specific compartment when voltages of levels 2, 4, 6, 8, 10, 12, and 14 are applied to a representative subject by the electrical stimulation device 10, and Figs. 8(b) and 8(c) are graphs showing the first and second derivatives. In this example, the voltages of the voltage levels 2, 4, 6, 8, 10, 12, and 14 are as follows, although not particularly limited thereto.
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

After extensive research, the inventors discovered that the relationship between the voltage for stimulating muscles and the conductivity of the muscles when that voltage is applied roughly follows a function that is a sigmoid function offset in the X-axis direction. In other words, they discovered that when the voltage for stimulating muscles is increased, the conductivity of the muscles increases slowly up to a certain voltage, then increases rapidly, and then increases slowly again. This characteristic can also be seen in Figure 8(a). When the conductivity follows this function, the voltage at which the second derivative is maximized will always be lower than the voltage at which the first derivative is maximized.

The inventors' tests on a large number of subjects have shown that some people begin to feel some pain from electrical stimulation at around the voltage at which the first derivative is at its maximum. As is clear from FIG. 8(b), once the voltage exceeds the voltage at which the first derivative is at its maximum, the increase in conductivity slows down even if the voltage is increased beyond that. In other words, the increase in the amount of muscle contraction slows down. Therefore, it can be said that applying a voltage above the voltage at which the first derivative is at its maximum does not improve the efficiency of training, despite the increased pain.

On the other hand, as mentioned above, the voltage at which the second differential value is maximized is always lower than the voltage at which the first differential value is maximized. Therefore, the voltage at which the second differential value is maximized can be said to be a safer (more comfortable) voltage than the voltage at which the first differential value is maximized. Furthermore, in a test conducted by the inventors on a large number of subjects, almost no one felt pain even when a voltage at which the second differential value was maximized was applied. Furthermore, the voltage at which the second differential value is maximized is not that low compared to the voltage at which the first differential value is maximized, and therefore the muscles can be contracted to a certain extent.

From the above, it can be seen that muscles can be trained safely and efficiently by determining the suitable voltage level based on the voltage at which the second derivative is maximized, i.e., the maximum voltage level.

In addition, according to this embodiment, the conductivity distribution of a specific muscle compartment is extracted, and a second-order differential value is calculated based on the extracted conductivity distribution. This makes it possible to more accurately determine the voltage level for a specific muscle compartment.

The present invention has been described above based on an embodiment. This embodiment is merely an example, and those skilled in the art will understand that various modifications are possible in the combination of each component and each processing process, and that such modifications are also within the scope of the present invention. Below, such modifications are described.

(Variation 1)
Although not specifically mentioned in the embodiment, there is a certain correlation between fat thickness and the preferred voltage level, and the thicker the fat, the higher the preferred voltage level tends to be. Therefore, in this modification, the fat thickness is specified, and a suitable voltage level candidate (hereinafter referred to as a suitable voltage level candidate) is specified from the specified fat thickness. Then, when the conductivity acquisition unit 50 acquires the conductivity distribution, voltages of a predetermined voltage level range based on the suitable voltage level candidate are sequentially applied. The following mainly describes the differences from the embodiment.

Figure 9 is a block diagram showing the functional configuration of the terminal 12 according to the modified example. The electrical stimulation intensity determination unit 40 of this modified example includes a conductivity acquisition unit 50, a compartment extraction unit 51, a differential value calculation unit 52, a preferred voltage determination unit 54, a fat thickness determination unit 56, a candidate determination unit 58, and a correspondence relationship storage unit 60.

The correspondence storage unit 60 stores correspondence data between the fat thickness of the attachment portion and suitable voltage level candidates. FIG. 10 is a diagram showing an example of the correspondence data. In this example, the correspondence data is data that associates a range of fat thickness with suitable voltage level candidates.

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

The fat thickness determination unit 56 determines the thickness of fat in the attached portion. The fat thickness determination unit 56 transmits a control instruction to the control unit 22 of the electrical stimulation device 10 to instruct the measurement of impedance. When the fat thickness determination unit 56 receives impedance data from the electrical stimulation device 10 in response to the control instruction, it reconstructs the conductivity distribution (tomographic image) of the attached portion. The reconstruction by the fat thickness determination unit 56 may be realized by a known reconstruction method. The fat thickness determination unit 56 determines the conductivity distribution of fat from the conductivity distribution of the attached portion, for example, by filter processing, based on the difference in conductivity between fat, muscle, and bone. The fat thickness determination unit 56 determines the thickness of fat from the determined conductivity distribution of fat. The fat thickness may be a representative value or a spatial average value.

The fat thickness may be determined by other methods, such as ultrasonic measurement. In this case, the fat thickness determination unit 56 may obtain the fat thickness determined by the other method.

The candidate determination unit 58 determines a suitable voltage level candidate from the identified fat thickness and the correspondence data stored in the correspondence storage unit. For example, if the fat thickness is 2.5 mm, the voltage level 3 is determined as the suitable voltage level candidate.

The conductivity acquisition unit 50 sequentially applies voltages of a predetermined range of voltage levels 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, and if the suitable voltage level candidate is Lc, for example, it may be a range from Lc-m to Lc+n (where m and n are both positive integers) or a range from 1 to Lc+n.

According to this modified example, the range of voltage levels at which the conductivity acquisition unit 50 acquires the conductivity distribution is limited, thereby shortening the time required to acquire the conductivity distribution and, in turn, to determine the preferred voltage level.

(Variation 2)
In the embodiment, the case where the measurement electrodes 20 are arranged in a row in the X direction has been described, but the present invention is not limited to this, and the measurement electrodes 20 may be arranged in multiple rows in the X direction. For example, the measurement electrodes 20 may be arranged in three rows on the opposite side of the first stimulation electrode 16 to the second stimulation electrode 18, between the first stimulation electrode 16 and the second stimulation electrode 18, and on the opposite side of the second stimulation electrode 18 to the first stimulation electrode 16. In this case, a conductivity distribution (tomographic image) of multiple layers can be obtained.

For example, the differential value calculation unit 52 calculates the second derivative of the conductivity with respect to the voltage value for each position of the specific compartment from the conductivity distribution of the specific compartment at each voltage level extracted from each of the conductivity distributions of the multiple layers. For example, the preferred voltage determination unit 54 determines the preferred voltage level based on the voltage level at which the spatial average of the second derivative (second difference value) at each position of the specific compartment in the multiple layers is maximized.

(Variation 3)
In the embodiment, the electrical stimulation device 10 is described as having only one pair of stimulation electrodes, but the present invention is not limited to this, and the electrical stimulation device 10 may have multiple pairs of stimulation electrodes, and the multiple pairs of stimulation electrodes may be arranged, for example, in the X direction. In this case, a voltage level may be determined for each pair of stimulation electrodes, in other words, for each compartment corresponding to each pair of stimulation electrodes.

For example, when the part to be worn is the lower leg, the electrical stimulation device 10 has two pairs of stimulation electrodes, and when the electrical stimulation device 10 is worn so that one pair of the stimulation electrodes electrically stimulates the gastrocnemius muscle and the other pair of the stimulation electrodes electrically stimulates the soleus muscle, the preferred voltage level may be determined for each muscle compartment of the gastrocnemius muscle and the soleus muscle, i.e., for each stimulation electrode pair. In this case, each member of the electrical stimulation intensity determination unit 40 may perform the respective processing for each muscle compartment, i.e., for each stimulation electrode pair. For example, first, the compartment extraction unit 51, the differential value calculation unit 52, and the preferred voltage determination unit 54 may perform their respective processing for the gastrocnemius muscle as the specific muscle compartment to determine the preferred voltage level for the gastrocnemius muscle, and then the compartment extraction unit 51, the differential value calculation unit 52, and the preferred voltage determination unit 54 may perform their respective processing for the soleus muscle as the specific muscle compartment to determine the preferred voltage level for the soleus muscle. In other words, the second derivative of the conductivity with respect to the voltage value is calculated for each of the multiple muscle compartments, and the suitable voltage level is determined based on the calculated second derivative.

(Variation 4)
In the embodiment, the case where the suitable voltage level (suitable voltage value) is determined based on the second derivative 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 of the conductivity with respect to the voltage value. In this case, the differential value calculation unit 52 calculates the first derivative of the conductivity with respect to the voltage value for each position of the specific compartment from the conductivity distribution of the specific compartment for each voltage level. Here, it is considered that the conductivity increases when the voltage level is increased, and when the voltage level is increased to a certain point, the conductivity does not increase even if the voltage level is increased further, that is, the increase in the conductivity stops and settles at a certain value. Therefore, even if the voltage level is increased further, the electrical stimulation becomes stronger and pain is felt, but the amount of muscle contraction does not increase much. In other words, even if the voltage level is increased further, the muscle cannot be trained efficiently and safely. Therefore, in this modified example, the voltage level at which the conductivity settles to a certain value is set as the suitable voltage level. When the conductivity settles to 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 of the conductivity with respect to the voltage value is 0 or a predetermined value or less as the suitable voltage level.

(Variation 5)
In the embodiment and the above-mentioned modified example, the case where the conductivity distribution of the attached part is obtained based on the impedance data has been described, but the dielectric constant or phase distribution of the attached part may be reconstructed based on the impedance data. In this case, the conductivity in the embodiment and the above-mentioned modified example may be read as "dielectric constant" or "phase".

(Variation 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-mentioned modified example. In this case, the electrical stimulation device 10 may include a display unit that the control unit 22 uses to notify the user.

Any combination of the above-mentioned embodiments and modifications is also useful as an embodiment of the present invention. The new embodiment resulting from the combination has the combined effects of each of the combined embodiments and modifications.

It will also be understood by those skilled in the art that the functions to be performed by each of the constituent elements described in the claims can be realized by each of the constituent elements shown in the embodiments and modifications individually or in combination with each other.

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 (9)

Stimulating electrodes for applying electrical stimulation to the muscles of a user;
a plurality of measurement electrodes for measuring the impedance of a user;
a differential value calculation unit that calculates a differential value of the electrical characteristic information based on the impedance measured by the plurality of measurement electrodes , the electrical characteristic information being based on the impedance that changes in response to the electrical signal applied to the stimulation electrode; and
An electrical stimulation system comprising: The electrical stimulation system of claim 1, wherein the differential value is a spatial average value in a predetermined space. The electrical stimulation system of claim 2, wherein the spatial average value is the spatial average of one muscle compartment. An 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. 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 values in the space to be displayed on a predetermined display unit. The electrical stimulation system according to any one of claims 1 to 5, wherein the differential value calculation unit calculates the differential value by differential approximation. An electrical stimulation system according to any one of claims 1 to 6, wherein the differential value is a second-order differential value. The electrical stimulation system according to claim 7, further comprising a determination unit that determines an electrical signal to be applied to the stimulation electrode that is suitable for the user based on the electrical signal among the electrical signals applied to the stimulation electrode that has the maximum second-order differential value. An electrical stimulation system according to any one of claims 1 to 8, wherein the electrical property information is electrical conductivity, dielectric constant or phase.

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