WO2022069678A1

WO2022069678A1 - Electric charge control for tens and nmes devices

Info

Publication number: WO2022069678A1
Application number: PCT/EP2021/077028
Authority: WO
Inventors: Vincent TELLENBACH
Original assignee: NMES Group AB
Priority date: 2020-09-30
Filing date: 2021-09-30
Publication date: 2022-04-07

Abstract

A system for providing electrical stimulation to muscles and nerves using a novel control method for the treatment of medical and non-medical conditions. Electrical stimulation is widely used among other things in medical applications for rehabilitation and pain management and in sport applications for muscle conditioning purposes. Neuromuscular Electrical Stimulation (NMES) or Transcutaneous Electrical Nerve Stimulation (TENS) consists of delivering short electrical impulses to the user. One of the critical safety parameters to control is the amount of electrical charge delivered by each impulse. This system includes an indirect control method to assess the amount of electrical charge, measured in Coulomb, delivered by the impulses. This control method is also used to optimize the power consumption of the stimulation device.

Description

Electric Charge Control for TENS and NMES Devices

Field of the Invention

The present invention relates, in general, to the use of electrical stimulation of muscles and nerves for the purpose of alleviating a broad range of medical conditions as well as for specific non-medical objectives.

Background

The number of medical applications that use electrical stimulation is large and covers virtually every living body component. These applications include prevention of muscle atrophy, promotion of wound healing, prevention of venous thrombosis, alleviation of both chronic/acute pain and prevention of incontinence to name but a few. Electrical stimulation may also be used for such non-medical objectives as muscle training, muscle toning, improving muscle endurance, and muscle relaxation.

Electrical stimulation of muscles and nerves is well established in medicine and physical therapy with a history dating back to mid-1850; such stimulation is currently achieved by applying electrodes to: 1) the skin at the point(s) of desired electrical stimulation; 2) through insertion of electrical probes into body cavities, and; 3) through surgical insertion of electrodes.

Neuromuscular Electrical Stimulation Principle

Muscle contractions are produced and controlled by the brain by means of electrical signals transmitted through the nervous system. When an electrical signal from the brain reaches the muscle, the latter is activated into groups of "motor units", each made up of a single neuron and of a group of associated muscle cells connected to it. This initiates a chemical reaction which causes the cells in this motor unit to contract. The complete contraction of the muscle usually involves a number of motor units simultaneously, and its strength is directly proportional to the number of activated motor units. The gradual enrolment process of the motor units which consents to a perfectly controlled and smooth muscle contraction is called spatial summation.

Electrical muscle stimulation (EMS), also known as neuromuscular electrical stimulation (NMES) or electromyostimulation, is the elicitation of muscle contraction using electric impulses. The impulses are generated by a device and are delivered through electrodes on the skin near to the muscles being stimulated. The electrodes are generally pads that adhere to the skin. The impulses mimic the action potential that comes from the central nervous system, causing the muscles to contract.

When a sufficiently intense single electrical impulse reaches the motor muscle or nerve, it causes one short single contraction of the muscle (spasm). If this single spasm is repeated and the frequency of reiteration exceeds ten spasms p.s., each following spasm is enhanced by one degree of muscle shortening caused by the preceding spasm. Such an effect is called temporal summation. The lowest stimulation frequency, where the successive contractions merge, is called tetanization frequency.

NMES Device Basics

The basic principle of a NMES device is shown on in Figure 1. The Power Supply (1) can be provided by either batteries, rechargeable batteries or a DC wall adapter. This power supply is forwarded (2) to the Voltage Boost Converter (4) stage that will increase the voltage. The boosted voltage is then forwarded to the Switching stage (10) in order to be shaped in the desired waveform. The waveform may be one of many different types: rectangular (monophasic, biphasic, symmetrical, asymmetrical...), sinusoid, sawtooth, high voltage peak, direct current. The waveform is then delivered to the stimulated object (11).

Electrical Charge

Electric charge is the physical property of matter carried by some elementary particles that governs how the particles are affected by an electric or magnetic field. Electric charge, which can be positive or negative, occurs in discrete natural units and is neither created nor destroyed.

Electric charges are of two general types: positive and negative. Two objects that have an excess of one type of charge exert a force of repulsion on each other when relatively close together. Two objects that have excess opposite charges, one positively charged and the other negatively charged, attract each other when relatively nearby. Electric charge is conserved: in any isolated system, in any chemical or nuclear reaction, the net electric charge is constant. The algebraic sum of the fundamental charges remains the same.

The unit of electric charge in the meter-kilogram-second and SI systems is the coulomb and is defined as the amount of electric charge that flows through a cross section of a conductor in an electric circuit during each second when the current has a value of one ampere. One coulomb consists of 6.24 x 10¹⁸ natural units of electric charge, such as individual electrons or protons. From the definition of the ampere, the electron itself has a negative charge of 1 .602176634 x 10^-19 coulomb.

Formula

q = electric charge in coulombs [C] tj = initial time t_f = final time

I = electric current in amperes [A] dt = time difference in seconds [s]

Measurement of Electric Charge - Common Approach

The common approach to measure the electric charge delivered by a NMES device is to have additional electronic components performing a current integrator function. These components will be generally added after the Switching stage. Figure 1 also shows this additional Current Integrator (13) that provides feedback (14) to the device central Processor unit (7).

Current Integrator Based on Capacitor

The simplest method to implement a current integrator consists of a Capacitor mounted in series with the load representing the stimulated object. Figure 2 represents this circuit where resistor R1 represents the stimulated object and where voltage Vc on capacitor C1 will increase accordingly to the following formula:

/(t) ■ dt dV(t) =

For a constant current lin, the corresponding electric charge is: q = I(t) ■ dt

Replacing the expression /(t) ■ dt in the previous equation gives the relation between the voltage measured on capacitor C1 , the value of capacitor C1 and the electric charge: q = dV (t) ■ C Current Integrator based on Operational Amplifier

A more reliable but more complex method to implement a current integrator consists of using two operational amplifiers. The first operational amplifier will be used as a current to voltage converter and the second operational will be used as integrator. Figure 3 represents this method where R1 is the stimulated object, where UTA is the differential amplifier and U1 :B is the integrator. Assuming R3 = R4 and R5 = R6, the output voltage Vdiff of U1 :A is:

Assuming C1 is a perfect level shifter and does not affect the short impulses provided by UTA, the output voltage Vint of U1 :B is:

Vdiff (t) dt R2 ■ Iin(t) ■ R5 dt Vint(t) = - = - J R7 C2 R7 ■ R3 C2

Using the electric charge delivered to the stimulated object R1 q

■ dt, the previous formula can be updated with:

R2 ■ Iin(f) ■ R5 dt R2 ■ R5 V^int(t) ~ R7 - R3 C2 ~ ^q ' R7 ■ R3 ■ C2

The electrical charge can be determined based on U1 :B output voltage with the following formula:

Known systems thus rely on a current integrator to calculate the charge delivered by the NMES device.

Summary

The invention is defined by the appended independent claims. Embodiments of the invention are defined in the dependent claims. An object of the present invention to provide a system for electric stimulation that uses a control method to indirectly determine the amount of electrical charge delivered by the stimulation device to the user at each impulse. A further object of the present invention to provide an alternative to the current practice of adding extra electronic components in order to measure the electrical charge. A further object of the present invention is to use an electrical charge calculation in order to optimize the power consumption of the stimulation device. A primary object of the present invention is to provide electric stimulation delivery that overcomes shortcomings in prior art devices. A secondary object of the present invention is to provide an electric stimulation method, using indirect electrical charge measure, which delivers electrical impulses that trigger strong, effective muscle contractions or nerve responses in a stimulated object (individual). Another object of the present invention is to provide an electric stimulation device that may be safely operated by medical and non-medical users, and that is simple and safe to use. A still further object of the present invention is to provide electric stimulation that is cost and size effective for both professionals and users.

The object of the present invention is to provide a new method to estimate electrical charge in an apparatus for providing electrical stimulation to muscles and/or nerves without adding any additional electronic component. This is advantageous because a reduction in the number of electrical components comprised within the device leads to reduced system complexity, i.e . , fewer potential points of failure. Furthermore, the power requirements of the device can be reduced due to the presence of fewer electrical components.

In a first aspect, there is provided an apparatus for providing electrical stimulation to muscles and/or nerves, comprising: a conductive medium configured to transfer electrical current to a user; a switching stage, connected to the conductive medium and configured to apply voltage to the conductive medium over a stimulation impulse having a time period; and a processor, configured to instruct the switching stage to generate the stimulation impulse, and configured to calculate the charge applied by the switching stage during the stimulation impulse based on the change in voltage applied by the switching stage over the time period. It may also be said that the apparatus may not comprise a current integrator and/or that the switching stage is connected directly to the conductive medium.

Exceeding a certain amount of electrical charge per impulse can be harmful for the user. The present invention recognises that charge delivered is an important parameter to calculate and control. The present invention removes the need for a current integrator to calculate the charge delivered through the conductive medium. In other words, the invention enables the measurement of the electrical charge delivered to the user without adding extra electronic components. This is advantageous for a number of reasons.

Size

It is advantageous for devices suitable for providing electrical stimulation to muscles and/or nerves to be as small as possible. Some forms of such devices may need to be worn during exercise, such that both weight and physical size are important parameters, and even those worn while the user is stationary may be advantageously reduced in size to aid portability and ease of use. Reducing the number of electrical components in the device reduces both the weight and size of the device.

Power consumption

By calculating current using change in voltage delivered, rather than with an additional electrical component, such as a current integrator, fewer electrical components are included within the device. The power consumption of the device is therefore reduced. This may be advantageous to reduce the heat and noise generated by the device. Furthermore, if the device incorporates a portable power supply, for example a battery, the power supply may be made smaller while maintaining similar device run time and/or the run time may be increased for a certain size of power supply.

Accuracy and speed of control

By avoiding the need to use a current integrator, and instead utilising a voltage change calculation, the invention provides more accurate calculation of charge delivered by the device, and can obtain a value for charge delivered more quickly. The increased speed and accuracy further improves power consumption of the device and allows for faster feedback to instruct next steps for the device, such as a subsequent stimulation impulse.

As a preferred embodiment, the present invention may be used to treat or improve any muscular or neural condition that is alleviated through use of electrical stimulation.

The apparatus may further comprise a power supply; and a boost converter, comprising a capacitor, the boost converter being connected to the power supply and to the switching stage and being configured to increase the input voltage from the power supply before applying an increased output voltage to the switching stage via the capacitor. By using a boost converter, the voltage at the start of the stimulation impulse can be increased, versus the voltage output by the power supply, and can also be controlled by the processor. The processor thus has greater flexibility in the stimulation impulses it can generate.

The apparatus may store a capacitance value of the capacitor at the processor, and the processor may be configured to receive, from the boost converter, a measurement of: the voltage at the start of the time period; and the voltage at the end of the time period, and is configured to calculate the charge applied by the switching stage based on the change in voltage applied by the switching stage over the stimulation impulse and the known capacitance value.

The boost converter may further comprise: an inductor; and a switch, wherein the switch is configured to move the boost converter between a charging state, in which the inductor is charged by the power supply, and a discharging state, in which the capacitor discharges via the switching stage, and wherein the switch is configured to cycle between the states according to a duty cycle.

The processor may be further configured to: disable cycling of the switch and set the boost converter in the discharging state, before generating the stimulation impulse; and restart cycling of the switch after generating the stimulation impulse and after measuring the change in voltage applied by the switching stage over the stimulation impulse.

In this way, the power supply is never connected directly to the switching stage, and the switch does not attempt to charge the capacitor during discharge through the switching stage. This allows the switching stage to provide voltage to the conductive medium stemming only from the capacitor in the boost converter.

The processor may be configured to control the charge applied by a subsequent stimulation impulse at least by adjusting the time period. Alternatively, or additionally, the processor may be configured to control the charge applied by a subsequent stimulation impulse at least by adjusting the duty cycle of the switch.

In this way, an effective and safe stimulation impulse can be generated by the processor, based on fast and accurate feedback obtain from the charge calculation performed. The stimulation impulses can be modified to ensure that the correct amount of charge is applied; the correct amount of charge meaning that it is effective in stimulating the muscles and/or nerves but is not painful or damaging to the user. The conductive medium may comprise: a conductive garment; a conductive accessory; or one or more hydrogel electrodes. In this way, the conductive medium may be able to apply charge where it is desired and/or effective for a user.

The apparatus may further comprise a user interface, the user interface being configured to receive user input of a manual adjustment to the charge applied by the subsequent stimulation impulse, and transmit the manual adjustment to the processor.

In a second aspect, there is provided a system comprising: an apparatus as herein before described; and a mobile device, having stored thereon an application configured to receive user input of a manual adjustment to the charge applied by the subsequent stimulation impulse, and transmit the adjustment to the processor.

By allowing a manual adjustment of the stimulation impulse, the user can have some control over the stimulations that they receive. If, for example, despite a calculation that the stimulation impulse will be effective, but the user is not experiencing sufficient stimulation, they could increase the charge. Alternatively, if the user experiences pain at a lower charge threshold than the calculation would suggest, they can reduce the charge of the subsequent stimulation impulse.

The processor may be configured to generate the subsequent stimulation impulse based on one or more manual adjustments and transmit the subsequent stimulation impulse to the switching stage.

In a third aspect of the invention, there is provided a method for operating an apparatus or system as hereinbefore described. The method may be used for medical and/or non-medical purposes. In some embodiments, the method may be used for non-medical purposes, for example, but not limited to, muscle conditioning.

In a fourth aspect, the present invention provides a system for stimulation of muscle and nerves that comprises:

A stimulation device with embedded electronic and firmware capable of safe and effective transmission of electrical stimulation signals.

A conductive media that could be presented as, but not limited to, a garment, a conductive accessory or hydrogel electrodes that enables safe and effective transmission of electrical stimulation signals. The foregoing and other objects and advantages will appear from the descriptions that follow. In the description reference is made to the accompanying drawings, which forms a part hereof, and in which is shown by way of illustration specific principles of the control method in which the invention may be practiced. These principles will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other principles may be utilized and that structural changes may be made without departing from the scope of the invention, for example, modifications in algorithms.

Brief Description of the Drawings

Figure 1 depicts an example of a prior art device for providing stimulation to muscles and/or nerves, which is not an embodiment of the present invention.

Figure 2 depicts an example of a prior art current integrator circuit, which is not an embodiment of the present invention.

Figure 3 depicts an example of a prior art current integrator circuit using two operational amplifiers, which is not an embodiment of the present invention.

The present invention may be more completely understood when considered in conjunction with the attached drawings, in which like reference characters designate the same or similar components throughout the several views, and in which:

Figure 4 depicts an apparatus for providing electrical stimulation to muscles and/or nerve according to the invention.

Figure 5 depicts a DC-DC Step-Up voltage booster for use with embodiments of the present invention.

Figure 6 depicts a voltage waveform that may be generated during a stimulation impulse by apparatus, systems, and methods according to the invention.

Figure 7 depicts a DC-DC Step-Up voltage booster for use with embodiments of the present invention. Detailed Description

Figure 4 shows a block diagram of the stimulation device where (1 ) is the power supply element that provides electrical energy to the whole device (2)(3), (4) is the DC-DC boost converter element that boosts the voltage provided by (1) up to the desired level (8), (5) is the feedback of the voltage of the DC-DC booster converter element that will be treated by the processor (7) in order to determine the electrical charge, (6) is the DC-DC boost converter duty cycle that will be optimized accordingly to the determined electrical charge and (9) is the control of the switching stage (10) that generates the electrical impulses delivered to the user (11).

The power supply (1) may be any device suitable to deliver a voltage to the DC-DC boost converter element (or voltage booster or boost converter) and/or to the switching stage. The power supply (1) may be a connection to an external source of power, for example connections to a mains voltage supply, or may be a self-contained unit, for example a battery or battery pack. The power supply (1 ) may deliver power to the voltage booster and/or switching stage via a direct physical connection or by a wireless power transfer means, such as electromagnetic induction.

The boost converter (4) may be any form of DC-DC voltage boost converter as may be apparent to a person skilled in the art. Particular boost converters for use with the present invention will be described in greater detail herein.

The voltage information (5) from the boost converter to the processor comprises the actual voltage delivered by the boost converter at the beginning of the stimulation impulse and the actual voltage delivered by the boost converter at the end of the stimulation impulse. Alternatively, and not shown, the switching stage (10) may communicate the start and end voltages to the processor, for example if no boost converter is used.

The processor (7) then determines the charge applied to the user during the stimulation impulse based on the start voltage (Vs: 13 in Figure 6) and end voltage (Ve: 13 in Figure 6), and a known capacitance value of the discharging capacitor (as described, for example, in Example 1). The processor (7) calculates the difference between Vs and Ve, and multiplies the result by the capacitance value (C) of the discharging capacitor to determine the charge applied (q) over the stimulation impulse (12 in Figure 6).

Alternatively, the capacitance value of the discharging capacitor may be calculated by the processor (7) based on the change in actual voltage during the stimulation impulse, a calibration discharge time (t_discharge), and known calibration resistance values R1 and R2, as described in Example 2.

Communication between components of the apparatus as shown in Figure 4 may be via a wired connection, or may be wireless, for example if certain components are not physically connected to one another. For example, the processor may be physically wired to the power supply, boost converter, and switching stage. Alternatively, the processor may communicate wirelessly with one or more additional processors on the power supply, boost converter, or switching stage.

Additionally, not shown, the processor (7) may be comprised on a mobile device, or a mobile device may be used to communicate with a processor (7) local to the apparatus.

Figure 5 shows an example of a boost converter for use in certain embodiments of the present invention.

Principle of Step-Up voltage booster

The key principle that drives the boost converter as shown in Figure 5 is the tendency of an inductor to resist changes in current by either increasing or decreasing the energy stored in the inductor magnetic field. In a boost converter, the output voltage is always higher than the input voltage.

(a) When the switch is closed, current flows through the inductor in the clockwise direction and the inductor stores some energy by generating a magnetic field. Polarity of the left side of the inductor is positive.

(b) When the switch is opened, current will be reduced as the impedance is higher. The magnetic field previously created will be reduced in energy to maintain the current towards the load. Thus, the polarity will be reversed (meaning the left side of the inductor will become negative). As a result, two sources will be in series causing a higher voltage to charge the capacitor through the diode D.

If the switch is cycled fast enough, the inductor will not discharge fully in between charging stages, and the load will always see a voltage greater than that of the input source alone when the switch is opened. Also, while the switch is opened, the capacitor in parallel with the load is charged to this combined voltage. When the switch is then closed and the right-hand side is shorted out from the left-hand side, the capacitor is therefore able to provide the voltage and energy to the load. During this time, the blocking diode prevents the capacitor from discharging through the switch. The switch must of course be opened again fast enough to prevent the capacitor from discharging too much.

• in the On-state, the switch S (see figure 5) is closed, resulting in an increase in the inductor current;

• in the Off-state, the switch is open and the only path offered to inductor current is through the flyback diode D, the capacitor C and the load R. This results in transferring the energy accumulated during the on-state into the capacitor.

In an apparatus according to the invention, switch S can be driven either by a dedicated integrated chip driven by the processor or directly by the processor.

It will be appreciated that although the invention has been described with reference to a DC-DC step-up boost converter, any capacitive source of voltage is suitable for use with the present invention. A calculation of charge delivered may be calculated with or without a voltage booster, based on the equation in step 4 of Example 1 . In such cases, the switching stage may communicate the voltage at the start and end of the stimulation impulse to the processor.

Furthermore, alternative regulator topologies to a DC-DC step-up boost converter may be used. Suitable alternative regulator topologies include, but are not limited to: a single-ended primaryinductor converter (SEPIC); a buck-boost converter; and a flyback converter. Indeed, if no voltage boosting is used at all, a power supply comprising a discharging capacitor may also be used. In this case, the processor may use a known capacitance value of the discharging capacitor in the power supply in order to calculate the charge applied to the user during a stimulation impulse.

In embodiments not using a voltage booster having a duty cycle, although control of the charge delivered for a subsequent stimulation impulse may not be controllable by varying the duty cycle of the voltage booster, the charge for the subsequent stimulation impulse may still be controlled by the processor by controlling the time period.

Figure 6 shows a typical waveform (12) of an electrical impulse generated by the stimulation device where (13) is the voltage on the DC-DC boost converter capacitor at the beginning of the electrical impulse and (14) is the voltage at the end of the electrical impulse. As described above, the processor (7) uses the start voltage (13), Vs, and the end voltage (14), Ve, along with either a known or calculated capacitance value, to determine the change in voltage over the stimulation impulse. This change in voltage value can be used by the processor (7) to determine the charge (q) applied over the stimulation impulse, as detailed in Examples 1 and 2. Waveforms in accordance with the present invention consist of rectangular impulses that could be either regulated in voltage or electrical current, monophasic or biphasic and symmetrical or asymmetrical. The processor (7) can identify start and end voltages, Vs and Ve, for any such waveform, and can use the voltages to calculate charge delivered (q).

Examples

Example 1

The following is an example of an operation of the processor operating to calculate charge delivered by a switching stage during a stimulation impulse, according to an embodiment of the invention.

1 . Processor disables switch S or the integrated chip controlling switch S.

2. Processor stores the value of the output voltage of the boost converter stage before generating the stimulation electric rectangular impulse (VboostStart).

3. Processor generates the stimulation impulse.

4. Processor measure the value of the output voltage of the boost converter stage at the end of the stimulation impulse (VboostStop) and compare that value with the value stored before the impulse was generated. The difference between the two value is related to the electric charge delivered to the stimulated object. q = dV(t) ■ C = (VboostStart — VboostStop) ■ C

5. Processor resumes normal operation of switch S.

In the step-up voltage booster used in the present invention, switch S presented in Figure 5 is implemented by either a bipolar or MOSFET transistor driven by a dedicated integrated chip or directly by the Processor. Figure 7 represents the boost converter used in the present invention. MOSFET transistor Q1 act as a switch. The signal G_DRIVE driven Q1 gate is a pulse-width- modulation (PWM) waveform generated by the main processor. A voltage divider consisting of resistor R1 and R2 provide feedback related to the output voltage VBOOST to the processor. This feedback FBACK_VBOOST is treated by the processor through an analog-to-digital conversion. If the feedback value is lower than the desired output voltage, the processor will activate the PWM signal driving transistor QI gate. If the feedback value is equal orabove the desired output voltage, the processor will disable the PWM signal.

First Step: Calibration

The capacitor C1 used in the voltage booster presented in Figure 7 has a typical tolerance 20%. Resistors R1 and R2 have a tolerance of 1 %. To overcome the effect of capacitor C1 wide tolerance margin, it is necessary to determine more accurately its value.

The calibration process consists in rising the voltage VBOOST up to a given value Veal and then let capacitor C1 discharge itself through resistors R1 and R2 and measure the duration needed for VBOOST to reach 37% of the initial value of Veal. Based on the capacitor discharge formula, 37% of the initial voltage correspond to the voltage reached after the duration of constant Tau or T. Tau is the time constant of an RC circuit that takes to change from one steady state condition to another steady state condition when subjected to a step change input condition.

Capacitor discharge formula:

When t = T:

0.37

T = R ■ c = (7?1 + /?2) ■ Cl

In the present case:

The value t_discharge should be stored in the non-volatile memory of the processor.

Second Step: Electric Charge Estimation during Electrical Stimulation

A method according to this example may be summarised as:

1 . Processor disable the PWM signal driving transistor Q1 gate or the integrated chip driving transistor Q1 gate.

2. Processor store the value of the output voltage of the boost converter stage before generating the stimulation electric rectangular impulse (VboostStart: figure 6, label 13).

3. Processor generates the stimulation impulse (figure 6, label 12).

4. Processor measure the value of the output voltage of the boost converter stage at the end of the stimulation impulse (VboostStop: figure 6, label 14) and compare that value with the value stored before the impulse was generated. The difference between the two values is related to the electric charge delivered to the stimulated object.

5. Processor resumes normal operation of the PWM signal driving transistor Q1 gate.

Embodiments

1. A system for providing electrical stimulation to muscles and nerves using a control method to determine the electrical charge delivered by each impulse.

2. The system of embodiment 1 wherein the control method is used to transmit the electrical stimulation from the stimulation device to the user by the means of conductive garment, conductive accessory or hydrogel electrodes.

3. The system of embodiment 1 wherein the control method is accomplished using the voltage drop measured on the DC-DC boost converter capacitor between the start and end of the impulse. 4. The system of embodiment 1 wherein the control method consists in both electronic components and firmware algorithms to determine the electrical charge.

5. The system of embodiment 1 wherein the control method is used to optimize the power consumption of the stimulation device by adjusting the DC-DC boost converter duty cycle.

6. The system of embodiment 1 wherein the control method firmware algorithms can be adjusted by a mobile application.

7. The device of embodiment 1 wherein the firmware programmed in the processor can be updated by either wired or wireless communication protocols.

8. A method for providing electrical stimulation to muscles and/or nerves, the steps comprising, at a processor: generating a stimulation impulse, the stimulation impulse having a time period; instructing a switching stage to apply the stimulation impulse through a conductive medium; and calculating a charge applied by the switching stage during the stimulation impulse based on a change in voltage applied by the switching stage over the time period.

9. The method according to embodiment 8, further comprising: operating a boost converter according to a duty cycle, wherein the boost converter is connected to a power supply and to the switching stage and is configured to increase the input voltage from the power supply before applying an increased output voltage to the switching stage via a capacitor.

10. The method according to embodiment 9, further comprising: storing a capacitance value of the capacitor; and wherein calculating a charge applied by the switching stage comprises: receiving, from the boost converter, a measurement of the voltage at the start of the time period; and receiving, from the boost converter, a measurement of the voltage at the end of the time period; and calculating the charge applied by the switching stage based on the change in voltage applied by the switching stage over the stimulation impulse and the known capacitance value.

11 . The method according to embodiment 9 or 10, wherein the boost converter further comprises: an inductor; and a switch, wherein the switch is configured to move the boost converter between a charging state, in which the inductor is charged by the power supply, and a discharging state, in which the capacitor discharges via the switching stage, and wherein the switch is configured to cycle between the states according to a duty cycle.

12. The method of embodiment 11 , further comprising: disabling cycling of the switch and set the boost converter in the discharging state, before generating the stimulation impulse; and restarting cycling of the switch after generating the stimulation impulse and after measuring the change in voltage applied by the switching stage over the stimulation impulse.

13. The method according to any one of embodiments 8 to 12, further comprising controlling the charge applied by a subsequent stimulation impulse at least by adjusting the time period.

14. The method according to any one of embodiments 9 to 13, further comprising controlling the charge applied by a subsequent stimulation impulse at least by adjusting the duty cycle of the switch.

15. The method according to any preceding embodiment, wherein the conductive medium comprises: a conductive garment; a conductive accessory; or one or more hydrogel electrodes. 16. The method according to any preceding embodiment, wherein the method does not utilize a current integrator.

17. The method according to any preceding embodiment, wherein the switching stage is connected directly to the conductive medium.

18. The method according to any one of embodiments 13 to 17, further comprising: receiving user input of a manual adjustment to the charge applied by the subsequent stimulation impulse; and transmitting the manual adjustment to the processor.

19. The method according to embodiment 18, wherein the manual adjustment is received at the processor via a user interface physically connected to the processor and/or remotely via an application stored on a mobile device.

20. The method according to embodiment 18 or embodiment 19, further comprising: generating the subsequent stimulation impulse based on one or more manual adjustments and transmit the subsequent stimulation impulse to the switching stage.

Claims

1. An apparatus for providing electrical stimulation to muscles and/or nerves, comprising: a conductive medium configured to transfer electrical current to a user; a switching stage, connected to the conductive medium and configured to apply voltage to the conductive medium over a stimulation impulse having a time period; and a processor, configured to instruct the switching stage to generate the stimulation impulse, and configured to calculate the charge applied by the switching stage during the stimulation impulse based on the change in voltage applied by the switching stage over the time period.

2. The apparatus according to claim 1 , further comprising: a power supply; and a boost converter, comprising a capacitor, the boost converter being connected to the power supply and to the switching stage and being configured to increase the input voltage from the power supply before applying an increased output voltage to the switching stage via the capacitor.

3. The apparatus according to claim 2, wherein a capacitance value of the capacitor is stored at the processor, and wherein the processor is configured to receive, from the boost converter, a measurement of: the voltage at the start of the time period; and the voltage at the end of the time period, and wherein the processor is further configured to calculate the charge applied by the switching stage based on the change in voltage applied by the switching stage over the stimulation impulse and the known capacitance value.

4. The apparatus according to claim 2 or claim 3, wherein the boost converter further comprises: an inductor; and a switch, wherein the switch is configured to move the boost converter between a charging state, in which the inductor is charged by the power supply, and a discharging state, in which the capacitor discharges via the switching stage, and wherein the switch is configured to cycle between the states according to a duty cycle.

5. The apparatus of claim 4, wherein the processor is further configured to: disable cycling of the switch and set the boost converter in the discharging state, before generating the stimulation impulse; and restart cycling of the switch after generating the stimulation impulse and after measuring the change in voltage applied by the switching stage over the stimulation impulse.

6. The apparatus according to any preceding claim, wherein the processor is configured to control the charge applied by a subsequent stimulation impulse at least by adjusting the time period.

7. The apparatus according to any one of claims 2 to 6, wherein the processor is configured to control the charge applied by a subsequent stimulation impulse at least by adjusting the duty cycle of the switch.

8. The apparatus according to any preceding claim, wherein the conductive medium comprises: a conductive garment; a conductive accessory; or one or more hydrogel electrodes.

9. The apparatus according to any preceding claim, wherein the apparatus does not comprise a current integrator.

10. The apparatus according to any preceding claim, wherein the switching stage is connected directly to the conductive medium.

11 . The apparatus according to any one of claims 6 to 10, further comprising a user interface, the user interface being configured to receive user input of a manual adjustment to the charge applied by the subsequent stimulation impulse, and transmit the manual adjustment to the processor.

12. A system comprising: an apparatus according to any one of claims 6 to 8; and a mobile device, having stored thereon an application configured to receive user input of a manual adjustment to the charge applied by the subsequent stimulation impulse, and transmit the adjustment to the processor.

13. The apparatus of claim 11 or the system of claim 12, wherein the processor is configured to generate the subsequent stimulation impulse based on one or more manual adjustments and transmit the subsequent stimulation impulse to the switching stage.

14. A method for operating an apparatus according to any one of claims 1 to 11 , or 13, or a system according to claim 12 or 13.

15. The method according to claim 14, where the method is for non-medical and/or muscle conditioning purposes.