Flex-MI

K221958 · Emsi, Inc. · IPF · Oct 21, 2022 · Physical Medicine

Device Facts

• Record ID: K221958
• Device Name: Flex-MI
• Applicant: Emsi, Inc.
• Product Code: IPF · Physical Medicine
• Decision Date: Oct 21, 2022
• Decision: SESE
• Submission Type: Traditional
• Regulation: 21 CFR 890.5850
• Device Class: Class 2
• Attributes: Therapeutic

Intended Use

Interferential Stimulation - > Symptomatic relief of chronic intractable pain - > Adjunctive treatment for the management of post-traumatic or post-surgical pain EMS (Electrical Muscle Stimulation) - > Relaxation of muscle spasm - > Increasing local blood circulation - > Muscle re-education - > Prevention or retardation of disuse atrophy - > Prevention of venous thrombosis of the calf muscles immediately after surgery - > Maintaining or increase range of motion

Device Story

Flex-MI is a prescription-use, battery-powered combination EMS and interferential (IF) stimulator. Device delivers electrical current to patient skin via electrodes to stimulate nerves or muscles. Input consists of user-adjustable settings for output and waveform; device features 2 output channels. Powered by 4.8V Ni-MH rechargeable battery. Includes patient compliance timer recording up to 999 hours. Used in clinical or home settings under clinician guidance. Output affects muscle/nerve activity to manage pain, spasms, circulation, and atrophy. Benefits include non-pharmacological pain management and physical therapy support.

Clinical Evidence

Bench testing only. No clinical data required to support substantial equivalence.

Technological Characteristics

Handheld, battery-powered (4.8V Ni-MH) stimulator. Plastic housing. 2 output channels. Regulated voltage. Microprocessor-controlled. Complies with IEC 60601-1, IEC 60601-1-2, IEC 60601-1-11, and IEC 60601-2-10. Software-based patient compliance timer. Compatible with self-adhesive electrodes.

Indications for Use

Indicated for symptomatic relief of chronic intractable pain, adjunctive management of post-traumatic or post-surgical pain, relaxation of muscle spasms, increasing local blood circulation, muscle re-education, prevention/retardation of disuse atrophy, prevention of venous thrombosis of calf muscles post-surgery, and maintaining/increasing range of motion.

Regulatory Classification

Identification

A powered muscle stimulator is an electrically powered device intended for medical purposes that repeatedly contracts muscles by passing electrical currents through electrodes contacting the affected body area.

Predicate Devices

• RS-4I Plus (K112348)

Reference Devices

• Flex MT Plus (K140467)
• Flex IT (K071869)

Submission Summary (Full Text)

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10/21/2022

EMSI, Inc. % Cherita James Regulatory Consultant M Squared Associates,Inc. 127 West 30th Street. 9th Floor New York, New York 10001

### Re: K221958

Trade/Device Name: Flex-MI Regulation Number: 21 CFR 890.5850, 21 CFR 882.5890 Regulation Name: Powered muscle stimulator Regulatory Class: Class II Product Code: IPF, LIH Dated: October 10, 2022 Received: October 11, 2022

#### Dear Cherita James:

We have reviewed your Section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food, Drug, and Cosmetic Act (Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. Although this letter refers to your product as a device, please be aware that some cleared products may instead be combination products. The 510(k) Premarket Notification Database located at https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm identifies combination product submissions. The general controls provisions of the Act include requirements for annual registration, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.

If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.

Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Part

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801); medical device reporting of medical device-related adverse events) (21 CFR 803) for devices or postmarketing safety reporting (21 CFR 4, Subpart B) for combination products (see https://www.fda.gov/combination-products/guidance-regulatory-information/postmarketing-safety-reportingcombination-products); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820) for devices or current good manufacturing practices (21 CFR 4, Subpart A) for combination products; and, if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR 1000-1050.

Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR Part 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part 803), please go to https://www.fda.gov/medical-device-safety/medical-device-reportingmdr-how-report-medical-device-problems.

For comprehensive regulatory information about medical devices and radiation-emitting products, including information about labeling regulations, please see Device Advice (https://www.fda.gov/medicaldevices/device-advice-comprehensive-regulatory-assistance) and CDRH Learn (https://www.fda.gov/training-and-continuing-education/cdrh-learn). Additionally, you may contact the Division of Industry and Consumer Education (DICE) to ask a question about a specific regulatory topic. See the DICE website (https://www.fda.gov/medical-device-advice-comprehensive-regulatoryassistance/contact-us-division-industry-and-consumer-education-dice) for more information or contact DICE by email ([e-mail]) or phone [phone] or 301-796-7100).

Sincerely,

For:

CDR Jitendra Virani, Assistant Director DHT5B: Division of Neuromodulation and Physical Medicine Devices OHT5: Office of Neurological and Physical Medicine Devices Office of Product Evaluation and Quality Center for Devices and Radiological Health

Enclosure

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# Indications for Use

510(k) Number (if known) K221958

Device Name Flex-MI

Indications for Use (Describe)

Interferential Stimulation

- > Symptomatic relief of chronic intractable pain
- > Adjunctive treatment for the management of post-traumatic or post-surgical pain

EMS (Electrical Muscle Stimulation)

- > Relaxation of muscle spasm
- > Increasing local blood circulation
- > Muscle re-education
- > Prevention or retardation of disuse atrophy
- > Prevention of venous thrombosis of the calf muscles immediately after surgery
- > Maintaining or increase range of motion

| Type of Use (Select one or both, as applicable) |
|-------------------------------------------------|
|-------------------------------------------------|

X Prescription Use (Part 21 CFR 801 Subpart D)

Over-The-Counter Use (21 CFR 801 Subpart C)

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# 510(K) SUMMARY

The following information is provided as required by 21 CFR § 807.87 for the Flex-MI 510(k) premarket notification. In response to the Safe Medical Devices Act of 1990, the following is a summary of the information upon which the substantial equivalence determination is based.

- Sponsor: EMSI, Inc 3504 Cragmont Dr. Suite#100 Tampa, Florida 33619 Telephone: [phone] Fax: [phone] Registration Number: 3003573572
- Cherita James Contact: M Squared Associates, Inc. 127 West 30th St, 9th Floor New York, New York 10001 Ph. 347-954-0624 Fax. [phone] Email: [e-mail]

Date of Submission: October 10, 2022

Proprietary Name: Flex- MI

Common Name: Combination EMS/Interferential stimulator

Regulatory Class: II

Regulation: 21 CFR 890.5850, 21 CFR 882.5890

Product Codes: IPF Powered Muscle Stimulator, LIH Interferential Current Therapy

Predicate Device(s): K112348 RS-4I Plus

Reference devices: K140467 Flex MT Plus, K071869 Flex IT (TENS/IF 14)

Device Description: The Flex-MI is a combination EMS and interferential stimulation device which delivers nerve or muscle stimulation by applying an electrical current to electrodes, which are attached on the patient's skin. The output and waveform is adjustable according to the intended treatment of patient. The stimulator has 2 output channels, accessed through jacks at the top of the housing, so that it may stimulate either 2 or 4 patient electrodes. The device is powered by 4.8V Ni- MH rechargeable battery pack. A patient compliance timer can memorize 60 sets of operation records; the total recordable time is

EMSI Inc

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999 hours. Flex-MI is compatible and recommended for use with Everlife self-adhesive electrodes (K012463).

#### Indications for Use

Interferential Stimulation

- > Symptomatic relief of chronic intractable pain
- > Adjunctive treatment for the management of post-traumatic or post-surgical pain

#### EMS

- > Relaxation of muscle spasm
- > Increasing local blood circulation
- > Muscle re-education
- > Prevention or retardation of disuse atrophy
- > Prevention of venous thrombosis of the calf muscles immediately after surgery
- > Maintaining or increase range of motion

#### Substantial Equivalence and Comparison to Predicate Devices

The claim of substantial equivalence of the Flex-MI combination EMS and interferential (IF) stimulator to the like modes of the products identified above is based on the comparison of the indications and intended use, product technical characteristics, performance characteristics and product handling. All devices are for prescription use.

Both the subject device, predicate device and the reference devices have the same indications and intended use for the IF and EMS modes. The primary predicate includes a more broad statement for IF, however the IF indications for the subject device are in-line with most IF devices cleared by the Agency as well as the reference IF device i.e. relief of acute and chronic pain. All devices are prescription devices and the appropriate treatment modality is the responsibility of the prescribing clinician. Based on the comparison in the following table the Flex-MI is substantial equivalent to the predicate device.

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| | Subject Device<br>Flex-MI<br>K221958 | Primary<br>RS-4I Plus K112348 | Reference K140467<br>Flex MT Plus (EMS<br>function) | Reference K071869<br>Flex IT (IF function) |
|--------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------|
| Product code | IPF, LIH | IPF, LIH | IPF | LIH |
| Indication for Use | IF- •Symptomatic<br>relief of chronic<br>intractable pain<br>•Post traumatic and<br>post surgical pain<br>relief<br>EMS- Electrical<br>Muscle Stimulation<br>•Relaxation of muscle<br>spasm<br>•Increasing local<br>blood circulation<br>•Muscle re-education<br>•Prevention or<br>retardation of disuse<br>atrophy<br>•Prevention of<br>venous thrombosis of<br>the calf muscles<br>immediately after<br>surgery<br>•Maintaining or<br>increase range of<br>motion | IF-<br>-Relieve acute pain<br>-Relieve and manage<br>chronic pain<br>EMS- Electrical<br>Muscle Stimulation<br>•Relaxation of muscle<br>spasm<br>•Increasing local blood<br>circulation<br>•Muscle re-education<br>•Prevention or<br>retardation of disuse<br>atrophy<br>•Prevention of venous<br>thrombosis of the calf<br>muscles immediately<br>after surgery<br>•Maintaining or<br>increase range of<br>motion | EMS- Electrical<br>Muscle Stimulation<br>•Relaxation of muscle<br>spasm<br>•Increasing local blood<br>circulation<br>•Muscle re-education<br>•Prevention or<br>retardation of disuse<br>atrophy<br>•Prevention of venous<br>thrombosis of the calf<br>muscles immediately<br>after surgery<br>•Maintaining or<br>increase range of<br>motion | IF- •Symptomatic<br>relief of chronic<br>intractable pain<br>• Post traumatic and<br>post surgical pain<br>relief |

Both the subject device and the predicate devices are battery powered, handheld devices with similar unit characteristics. Based on the comparison in the following table the Flex-MI is substantial equivalent to the predicate devices.

| | Subject Device<br>Flex-MI | Primary | Reference | Reference |
|---------------------------------------------------------------------|---------------------------------------------------------------------|------------------------------------------|---------------------------------------------------------------------|----------------------------------------------------------|
| | K221958 | RS-4I Plus | Flex MT Plus<br>(EMS function) | Flex IT (IF<br>function) |
| 1. 510(k) Number | Not assigned | K112348 | K140467 | K071869 |
| 2. Device Name,<br>Model | Flex-MI | RS-4I Plus | Flex MT Plus | Flex IT |
| 3. Manufacturer | EMSI/Everlife | RS Medical | EMSI/Everlife | EMSI/Apex<br>Medical |
| | Subject Device<br>Flex-MI | Primary<br>RS-4I Plus | Reference<br>Flex MT Plus<br>(EMS function) | Reference<br>Flex IT (IF<br>function) |
| | K221958 | | | |
| 4. Power Source | 500 mAh 4.8V Ni-<br>MH, rechargeable<br>battery pack and<br>charger | Lithium Ion battery<br>with charger | 700 mAh 4.8V Ni-<br>MH, rechargeable<br>battery pack and<br>charger | four batteries, size<br>AA, alkaline; or<br>adapter 6VDC |
| 5. Number of Output<br>Modes | 2 | 2 | 2 | 2 |
| 6. Number of Output<br>Channels | 2 | 4 | 2 | 2 |
| – Synchronous or<br>Alternating<br>– Method of<br>Channel Isolation | Synchronous or<br>Alternating<br>Transformer | Synchronous or<br>Alternating<br>unknown | Synchronous or<br>Alternating<br>Transformer | Synchronous<br>Transformer |
| 7. Regulated Current<br>or Regulated<br>Voltage? | Regulated Voltage | Regulated Voltage | Regulated voltage | Regulated voltage |
| 8.<br>Software/Firmware/<br>Microprocessor<br>Control? | Yes | yes | Yes | Yes |
| 9. Automatic<br>Overload Trip? | Yes | unknown | Yes | No |
| 11. Automatic Shut<br>Off? | Yes | Yes | Yes | Yes |
| 12. Patient Override<br>Control? | Yes | Yes | Yes | Yes |
| 13. Indicator Display: | Yes | Yes | Yes | Yes |
| On/Off Status? | Yes | Yes | Yes | Yes |
| Low Battery? | Yes | Yes | Yes | Yes |
| Voltage/Current<br>Level? | Yes (1-10 bars<br>displayed) | Yes 1-4 bars | Yes (1-10 bars<br>displayed) | Yes (1-10 bars<br>displayed) |
| 4. Timer Range<br>(minutes) | 5-90 minutes, or<br>continuous | 0-60 minutes | 5-90 minutes, or<br>continuous | 5-90 minutes, or<br>continuous |
| 15. Compliance with<br>Voluntary Standards? | IEC 60601-1-2 as<br>applicable | unknown | IEC 60601-1-2 as<br>applicable | IEC 60601-1-2 as<br>applicable |
| 16. Compliance with<br>21 CFR 898? | Yes | unknown | Yes | Yes |
| 17. Weight | 159g (including<br>battery) | 471g including<br>battery | 156 g (including<br>battery) | 140g |
| 18. Dimensions [W x<br>H x D] | 12cm x 5.4cm x<br>2.5cm | 3.2"x 8" x1.8" | 12 cm x 5.4cm x<br>3.3cm | 12 cm x 5.5cm x<br>2.5cm |
| | Subject Device<br>Flex-MI | Primary | Reference | Reference |
| | K221958 | RS-4I Plus | Flex MT Plus<br>(EMS function) | Flex IT (IF<br>function) |
| 19. Housing<br>Materials and<br>Construction | plastic | unknown | plastic | plastic |

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## Output Specifications

Both the subject device, predicate and the reference devices have similar output specifications and are within the range of currently marketed devices for the proposed intended uses.

Flex-MI and RS-41 Plus– Primary Predicate

| Output<br>Characteristics<br>EMS mode | Subject Device- Flex MI K221958 | | Primary -<br>RS-41 Plus K112348 | |
|-------------------------------------------|------------------------------------------------------------|------------------------------------------------------------------------|---------------------------------|-------------------------|
| Waveform | Asymmetrical<br>biphasic | Biphasic symmetrical | Asymmetrical<br>biphasic | Biphasic<br>symmetrical |
| Shape | Rectangular | | Rectangular | |
| Maximum Output<br>Voltage | 43.0V @ 500Ω | 43.0V @ 500Ω | 50V @ 500Ω | 50V @ 500Ω |
| Maximum Output<br>Current | 86.0mA @ 500Ω | 86.0mA @ 500Ω | 100mA @ 500Ω | 100mA @ 500Ω |
| Pulse Width per<br>phase | Positive 50-400µsec | | Positive 50-400µsec | |
| Max Phase<br>Duration<br>(Positive Phase) | 400µs =0.4ms | 400µs =0.4ms | unknown | unknown |
| Max Phase<br>Duration<br>(Negative Phase) | 2900µs =2.9ms | 400µs =0.4ms | 2.6ms | 400µs<br>=0.4ms |
| Pulse Frequency<br>Max Duty factor | 2~150.2Hz<br>400µs/(1/150.2Hz)<br>=0.4ms/6.66ms<br>= 0.060 | 2~150.2Hz<br>(400µs+400µs)/(1/150<br>.2Hz)<br>=0.8ms/6.66ms<br>= 0.120 | 71Hz | 71Hz |
| Multi-phasic<br>waveforms | Yes | Yes | Yes | Yes |
| Phase duration | Positive 50-400µsec | Positive 50-400µsec | 421µs<br>=0.421ms | 421µs<br>=0.421ms |

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| Output<br>Characteristics<br>EMS mode | Subject Device- Flex MI K221958 | Primary -<br>RS-4I Plus K112348 | |
|-------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------|---------|
| Net Charge<br>(µC per pulse) | Positive wave<br>$86.0mA*400\mu s$<br>$=86.0mA*0.4ms$<br>$= 34.4 @ 500\Omega$<br>Negative wave<br>$(-86mA/2)*400\mu s+(-$<br>$8mA/2)*2500\mu s$<br>$=(-43mA)*0.4ms+(-$<br>$4mA)*2.5ms$<br>$= - 17.2+(-10)$<br>$= - 27.2 @ 500\Omega$<br>$34.4+ (-27.2)$<br>$= 7.2 @ 500\Omega$ | unknown | |
| Maximum Phase<br>Charge<br>(μC) | Positive wave<br>$86.0mA*400\mu s$<br>$=86.0mA*0.4ms$<br>$= 34.4 @ 500\Omega$<br>Negative wave<br>$(-86mA/2)*400\mu s+(-$<br>$8mA/2)*2500\mu s$<br>$=(-43mA)*0.4ms+(-$<br>$4mA)*2.5ms$<br>$= - 17.2+(-10)$<br>$= - 27.2 @ 500\Omega$<br>$34.4+ (-27.2)$<br>$= 7.2 @ 500\Omega$ | unknown | |
| Surface Area of<br>Electrode | $4cm*4cm= 16cm^2$ | unknown | |
| Maximum Current<br>Density<br>(mA/cm²) | $28.1mA/16cm^2$<br>$= 1.76 @500\Omega$ | unknown | |
| Maximum Power<br>Density<br>(W/cm²) | Average Voltage<br>$43.0V*0.4ms/6.66ms$<br>$= 2.58V @ 500\Omega$<br>Average Current<br>$86.0mA*0.4ms/6.66m$<br>s<br>$= 5.17mA @ 500\Omega$<br>$2.58V*5.17mA/16cm^2$<br>$=2.58V*0.00517A/16$<br>$cm^2$<br>$= 0.000834 @500\Omega$ | unknown | |
| Output<br>Characteristics<br>EMS mode | Subject Device- Flex MI K221958 | Primary -<br>RS-4I Plus K112348 | |
| Maximum<br>Pulse Duration | 400μs+2900μs<br>=0.4ms+2.9ms<br>=3.3ms | 400μs+400μs<br>=0.4ms+0.4ms<br>=0.8ms | unknown |
| Additional<br>Features<br>(if applicable) | Patient compliance timer | Patient compliance timer | |

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Flex-MI and Flex MT Plus (EMS function)- Reference device

| Output<br>Characteristics<br>EMS mode | Subject Device- Flex MI K221958 | | Flex-MT +<br>K140467 | |
|-------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Waveform | Asymmetrical<br>biphasic | Biphasic<br>symmetrical | Asymmetrical<br>biphasic | Biphasic symmetrical |
| Shape | Rectangular | | Rectangular | |
| Maximum Output<br>Voltage | 43.0V @ 500Ω<br>107V @ 2kΩ<br>214V @ 10kΩ | 43.0V @ 500Ω<br>105V @ 2kΩ<br>214V @ 10kΩ | 43.2V @ 500Ω<br>150V @ 2kΩ<br>428V @ 10kΩ | 43.2V @ 500Ω<br>90V @ 2kΩ<br>344V @ 10kΩ |
| Maximum Output<br>Current | 86.0mA @ 500Ω<br>53.5mA @ 2kΩ<br>21.4mA @ 10kΩ | 86.0mA @ 500Ω<br>52.5mA @ 2kΩ<br>21.4mA @ 10kΩ | 86.4mA @ 500Ω<br>75.0mA @ 2kΩ<br>42.8mA @ 10kΩ | 86.4mA @ 500Ω<br>45.0mA @ 2kΩ<br>34.4mA @ 10kΩ |
| Pulse Width per<br>phase | Positive 50-400µsec | | Positive 50-400µsec | |
| Max Phase<br>Duration<br>(Positive Phase) | 400µs =0.4ms | 400µs =0.4ms | 400µs<br>=0.4ms | 400µs<br>=0.4ms |
| Max Phase<br>Duration<br>(Negative Phase) | 2900µs =2.9ms | 400µs =0.4ms | 2.6ms | 400µs<br>=0.4ms |
| Pulse Frequency | 2~150.2Hz | 2~150.2Hz | 2-151.5Hz | 2-151.5Hz |
| Max Duty factor | 400µs/(1/150.2Hz)<br>=0.4ms/6.66ms<br>= 0.060 | (400µs+400µs)/(1/<br>150.2Hz)<br>=0.8ms/6.66ms<br>= 0.120 | 400µsec/6.6ms<br>= 0.061 | 400µsec+400µsec<br>/6.6ms<br>= 0.121 |
| Multi-phasic<br>waveforms | Yes | Yes | Yes | Yes |
| Output<br>Characteristics<br>EMS mode | Subject Device- Flex MI K221958 | Flex-MT +<br>K140467 | | |
| Phase duration | Positive 50-<br>400µsec | Positive 50-<br>400µsec | Positive 50-400µsec | |
| Net Charge<br>(µC per pulse) | Positive wave<br>$86.0mA*400\mu s = 86.0mA*0.4ms = 34.4 @ 500\Omega$<br>Negative wave<br>(-<br>$86mA/2*400\mu s + -8mA/2*2500\mu s = -43mA*0.4ms + -4mA*2.5ms = -17.2 + -10 = -27.2 @ 500\Omega$<br>$34.4 + -27.2 = 7.2 @ 500\Omega$ | Positive wave<br>$86.0mA*400\mu s = 86.0mA*0.4ms = 34.4 @ 500\Omega$<br>Negative wave<br>$-86.0mA*400\mu s = -86.0mA*0.4ms = -34.4 @ 500\Omega$<br>$34.4 + -34.4 = 0 @ 500\Omega$ | Positive wave<br>$86.4mA*400\mu sec = 34.6 @ 500\Omega$<br>Negative wave<br>$86.4mA*400\mu sec = -34.6 @ 500\Omega$<br>$34.6 + -34.6 = 0 @ 500\Omega$<br>(symmetrical phases<br>result in 0) | |
| Maximum Phase<br>Charge<br>(µC) | Positive wave<br>$86.0mA*400\mu s = 86.0mA*0.4ms = 34.4 @ 500\Omega$<br>Negative wave<br>(-<br>$86mA/2*400\mu s + -8mA/2*2500\mu s = -43mA*0.4ms + -4mA*2.5ms = -17.2 + -10 = -27.2 @ 500\Omega$<br>$34.4 + -27.2 = 7.2 @ 500\Omega$ | Positive wave<br>$86.0mA*400\mu s = 34.4 @ 500\Omega$<br>Negative wave<br>$-86.0mA*400\mu s = -34.4 @ 500\Omega$<br>$34.4 + -34.4 = 0 @ 500\Omega$ | Positive wave<br>$86.4mA*400\mu sec = 34.6 @ 500\Omega$<br>Negative wave<br>$86.4mA*400\mu sec = -34.6 @ 500\Omega$<br>$34.6 + -34.6 = 0 @ 500\Omega$<br>(symmetrical phases<br>result in 0) | |
| Surface Area of<br>Electrode | $4cm*4cm= 16cm^2$ | $4cm*4cm (1.5in x 1.5in)= 16cm^2$ | | |
| Maximum Current<br>Density<br>(mA/cm²) | $28.1mA/16cm^2 = 1.76 @ 500\Omega$ | $42.8mA/16cm^2 = 2.68 @ 500\Omega$ | $29.2mA/4*4cm^2 = 1.83 @ 500\Omega$<br>(4cm*4cm<br>Electrode) | |
| Output<br>Characteristics<br>EMS mode | Subject Device- Flex MI K221958 | | Flex-MT +<br>K140467 | |
| Maximum Power<br>Density<br>(W/cm²) | Average Voltage<br>$43.0V*0.4ms/6.66 ms = 2.58V @ 500Ω$<br>Average Current<br>$86.0mA*0.4ms/6.66ms = 5.17mA @ 500Ω$<br>$2.58V*5.17mA/16 cm² =2.58V*0.00517A/16cm² = 0.000834 @500Ω$ | Average Voltage<br>$43.0V*0.4ms/6.66 ms = 2.58V @ 500Ω$<br>Average Current<br>$86.0mA*0.4ms/6.66ms = 5.17mA @ 500Ω$<br>$2.58V*5.17mA/16 cm² =2.58V*0.00517A/16cm² = 0.000834 @500Ω$ | Average Voltage<br>$43.2V*0.4ms/6.6ms = 2.62V @ 500Ω$<br>Average Current<br>$86.4mA*0.4ms/6.6 ms = 5.24mA @ 500Ω$<br>$2.62V*5.24mA/4*4 cm² = 0.000858@500Ω$<br>(4cm*4cm electrode) | Average Voltage<br>$43.2V*0.4ms/6.6ms = 2.62V @ 500Ω$<br>Average Current<br>$86.4mA*0.4ms/6.6ms = 5.24mA @ 500Ω$<br>$2.62V*5.24mA/4*4cm² = 0.000858@500Ω$<br>(4cm*4cm electrode) |
| Maximum<br>Pulse Duration | $400μs+2900μs =0.4ms+2.9ms =3.3ms$ | $400μs+400μs =0.4ms+0.4ms =0.8ms$ | $400μs+2.6ms =0.4ms+2.6ms =3.0ms$ | $400μs+400μs =800μs =0.8ms$ |
| Additional<br>Features<br>(if applicable) | Patient compliance timer | | Patient compliance timer | |

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Flex-MI and Flex IT (Interferential Function)- Reference device

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| Output Characteristics- IF mode | Subject Device- Flex MI<br>K221958 | K071869 Flex IT (IF function) |
|----------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------|
| Waveform | Square Wave | Square Wave |
| Shape | Rectangular | Rectangular |
| Maximum Output Voltage | 16.5V@500 Ω<br>27V@2kΩ<br>54.6 V@10 kΩ | 15 V @ 500 Ω<br>24 V @ 2 k Ω<br>28 V @ 10 k Ω |
| Maximum Output Current | 33mA@500Ω<br>13.5mA@2kΩ<br>5.5mA @10kΩ | 30 mA@ 500 Ω<br>12 mA @ 2 kΩ<br>2.8 mA @10 k Ω |
| INF: Beat Frequency | -188Hz to +387 Hz, max | -188 to + 387 Hz, max. |
| Pulse Width per phase | 125µs | 125 µs |
| Max Phase Duration<br>(Positive Phase) | 125µs = 0.125ms | 125µs = 0.125ms |
| Max Phase Duration<br>(Negative Phase) | 125µs = 0.125ms | 125µs = 0.125ms |
| Pulse Frequency | 4,000Hz | 4,000 Hz |
| Max Duty factor | | |
| Multi-phasic waveforms | Yes | Yes |
| Phase duration | 125 µs=0.125ms | 125 µs |
| Net Charge<br>(µC per pulse) | Positive wave<br>$33mA*125µs$<br>$=33mA*0.125ms$<br>$= 4.125@ 500Ω$<br><br>Negative wave<br>$(-33mA)*125µs$<br>$=(-33mA)*0.125ms$<br>$=(-4.125)@ 500Ω$<br><br>$4.125+ (-4.125)$<br>$= 0 @ 500Ω$ | $0@ 500Ω$<br>Symmetrical + and - halves |
| Maximum Phase Charge<br>(μC) | Positive wave<br>$33mA*125μs =33mA*0.125ms = 4.125 @ 500Ω$<br>Negative wave<br>$(-33mA)*125µsec =(-33mA)*0.125ms = (-4.125) @ 500Ω$<br>$4.125+(-4.125) = 0 @ 500Ω$ | $3 @ 500Ω$ |
| Surface Area of Electrode | $4cm*4cm = 16cm^2$ | $1.5 inches*1.5inches=2.25in^2$ |
| Maximum Current Density<br>(mA/cm²) | $33mA(@500Ω)/16cm^2 = 2.06 @ 500Ω$ | $2.08 @ 500Ω$ 1.5 in electrode |
| Maximum Power Density<br>(W/cm²) | Average Voltage<br>$16.5V*125μs/(1/4000Hz) =16.5V*0.125ms/0.25ms = 8.25V @ 500Ω$<br>Average Current<br>$33mA*125µs/(1/4000Hz) =33mA*0.125ms/0.25ms = 16.5mA @ 500Ω$<br>$8.25V*16.5mA/16cm^2 =8.25V*0.0165A/16cm^2 = 0.009 @ 500Ω$ | $0.031 @ 500Ω$ |
| Maximum<br>Pulse Duration | 125 μs | 125 μs |
| Additional Features<br>(if applicable) | Patient compliance monitor | Patient compliance monitor |

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### Compliance with Standards

The Flex-MI was designed and tested to conform with the following FDA-recognized standards:

| Standard | Recognition<br>Number |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------|
| IEC 62366-1 Edition 1.0 2015-02<br>Medical devices - Part 1: Application of usability engineering to medical devices<br>[Including CORRIGENDUM 1 (2016)] | 5-114 |
| ISO 14971 Third Edition 2019-12<br>Medical devices - Application of risk management to medical devices | 5-125 |
| ANSI AAMI ES60601-1:2005/(R)2012 and A1:2012, C1:2009/(R)2012 and<br>A2:2010/(R)2012 Medical electrical equipment - Part 1: General requirements for basic<br>safety and essential performance (IEC 60601-1:2005, MOD) | 19-4 |
| IEC 60601-1-11 Edition 2.0 2015-01 Medical electrical equipment - Part 1-11: General<br>requirements for basic safety and essential performance - Collateral Standard: | 19-14 |

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| Standard | Recognition<br>Number |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------|
| Requirements for medical electrical equipment and medical electrical systems used in the<br>home healthcare environment. | |
| IEC 60601-2-10 Edition 2.1 2016-04 Medical electrical equipment - Part 2-10: Particular<br>requirements for the basic safety and essential performance of nerve and muscle<br>stimulators | 17-16 |
| IEC 60601-1-2, Medical Electrical Equipment, Part 1: General Requirements for Safety.<br>Collateral Standard: Electromagnetic Compatibility- Requirements and Test. | 19-8 |

Clinical Data: Clinical data is not required to support the substantial equivalence to the predicate devices.

Conclusion: Based on the Flex-MI and the predicate device's technical characteristics, performance, and indications for use, the subject device is substantially equivalent to the predicate device. The subject device performs as intended for the same indications as the predicate devices with regard to EMS and IF functions.