TENS Therapy

Effective Pain Relief with TENS Unit​

By Mahnoush Rodriguez
Last Updated: September 9, 2018

❯ Pain Management

TENS therapy relieves pain by sending electrical pulses through the skin using a device called TENS unit.

In this article, you’ll get an overview of what TENS therapy is, how a TENS unit works, what factors affect TENS effectiveness, how it can be used safely and what are the best TENS units in the market.

Important Note

DoctorsConvey does not provide medical advice, diagnosis or treatment. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. Learn more


TENS Therapy for Pain Management

About 40 million US adults have pain every day or most days and another 87 million have pain on some days, according to the 2012 National Health Interview Survey.¹

When pain becomes chronic, it can bring a stack of other problems such as sleep disorders, anxiety, depression, and poor overall health.¹

A lot of efforts have been made over the years to find solutions for pain control. TENS therapy is one of them.

TENS stands for transcutaneous electrical nerve stimulation.

It is an inexpensive non-drug therapy commonly used for managing acute and chronic pain.²


TENS is considered a pain relief method, and it doesn’t cure the underlying cause of pain.³

In this therapy, a device called TENS unit is used to control pain.

How TENS Unit Works

TENS unit or TENS machine is a small portable device with three main components:

  • A power unit where you can turn ON/OFF the machine and adjust the settings
  • Electrodes with sticky pads to deliver electrical current to the skin
  • Wires – often dual wires – that connect the electrodes to the power unit


During the treatment, the electrodes are placed on the intact skin near the source of pain.


When the unit is ON, the power unit sends mild electrical impulses to the skin through electrodes.
This stimulates underlying nerves and alleviates pain.⁴

How TENS machine reduces pain

TENS therapy activates a complex network of nerve cells and responses in the body that results in pain reduction.⁵

When you use a TENS unit, it produces signals according to the frequency you set in the machine.
These signals activate nerve fibers that carry electrical pulses to the central nervous system.
The brain and spinal cord in the central nervous system interpret the received signals and inhibit the perception of pain.⁵

TENS also reduces pain by stimulating the central nervous system to release natural pain relief chemicals in the body.²

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TENS Unit Settings

Several stimulation parameters can be set and adjusted in a TENS machine.
Each of these settings has a different function and can influence the success of therapy.

Most TENS units come with the manufacturer’s instruction manual. The manual often explains how the unit should be used.

The standard adjustable parameters in the device include:

  1. Pulse frequency (pulse rate)
  2. Pulse intensity (pulse amplitude)
  3. Pulse width (pulse duration)

The below information and specifications are general and may vary according to the type of TENS unit being used. Consult with your doctor or healthcare provider for detailed instructions.

① TENS pulse frequency (pulse rate)

Pulse frequency, also called pulse rate, is the number of electrical pulses the device sends in one second.
Generally, higher frequencies feel more comfortable and give you a feeling of more continuous current.

Frequency is measured in Hertz (Hz).
You can adjust the frequency in most TENS units. The adjustable range is usually between 1Hz to 150Hz.

❱ Lower frequency versus higher frequency

The nerves in the body respond to different pulse rates or frequencies. Low frequencies, usually below 10Hz, activate different nerve groups and responses than high frequencies, above 50Hz.²

At any given intensity, lower frequencies make the body to produce pain relief chemicals naturally. On the other hand, higher frequencies interfere with the pain signals sent through the nerves. This interference prevents pain signals to reach the brain and be interpreted as pain.

Acute pains usually respond to higher frequencies like 80Hz to 120Hz.
Chronic pains may benefit from lower frequencies in the range of 2Hz to 10Hz.
Mid-range frequencies, 35Hz to 50Hz, are usually used for muscle stimulation and strengthening.

② TENS pulse intensity (pulse amplitude)

Pulse intensity, also called pulse amplitude, indicates the pulse peak and the depth and strength of the pulse. It is measured in milliamps (mA) which is one-thousandth of an ampere.

Higher intensities make the stimulation feel stronger and more powerful.

TENS waveforms in TENS units usually have a range of 0mA to 100mA.

In a lower intensity setting, also called sensory intensity, you may feel a strong but comfortable sensation. Higher intensity setting, also called motor intensity, can produce a tingling feeling or tiny muscle twitches that are not painful.⁶

③ TENS pulse width (pulse duration)

Pulse width, also called pulse duration, indicates the length of time for each stimulation and how wide the pulse is. It is measured in microseconds (uS or µs). Each microsecond is one-thousandth of a second.

In most TENS units you can adjust the pulse width somewhere between 30uS to 300uS. This range in seconds equals 0.03 to 0.3 second.

Pretty short, right?

Even though it may appear the increments in such a brief period shouldn’t matter, they do. Your nerves would distinguish the difference and react accordingly.

The pulse width typical setting is around 175uS to 200uS.
The stimulation is more shallow in lower pulse width, and TENS feels more comfortable. However, if it is too low, you may not feel any stimulation.
As the pulse width increases, the stimulation goes deeper and becomes more aggressive. In this case, the sensation becomes stronger and more uncomfortable. If the pulse width is set too high, it can cause muscle contractions.

Low to mid pulse width seems to be more effective in pain relief. Longer pulses are usually used for muscle stimulation.

Common TENS unit modes

Many TENS units have pre-programmed modes with preset parameters.

Below are the most common ones:

► Burst mode TENS

In this mode, the device bursts few pulses at once rather than in a continuous fashion.

It is usually set for 2 to 3 bursts per second.

► Modulation mode TENS

In this mode, the unit makes TENS stimulation patterns variable and more irregular.

The pulse variations could be due to changing the frequency, intensity or pulse width.

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TENS Treatment Dose and Application

When you decide to do this therapy, it’s important you know about the specifics of the treatment such as how long each treatment should last or how many times a day you need to do it.


TENS therapy dosing describes these details about the TENS application.

A dose of TENS treatment specifies:⁵

  • Location of electrodes
  • Pulse frequency
  • Pulse intensity
  • Pulse width
  • Duration of each treatment session
  • Number of treatments per day
  • Number of days of TENS therapy

TENS dosing example:

TENS therapy of shoulder, set at a low frequency of 5Hz, with a pulse width of 175uS at maximum tolerable intensity for 10 minutes, twice a day for 3 days.

TENS applications

The most common types of TENS applications are:⁴

  • Conventional TENS
  • Acupuncture‐like TENS

► Conventional TENS

In this traditional application, the frequency is set to high and intensity is often set to low. This application creates a comfortable tingling sensation at the site of electrodes.⁴

► Acupuncture‐like TENS

In this application, the frequency is set to low and intensity to high. This application often causes muscle twitches and contractions at the area where the electrodes are placed.⁴

There is no “one size fits all” treatment

Many clinical studies have been conducted to assess TENS effectiveness.
Despite that, it is still unclear what pain conditions can benefit from TENS the most and what parameters settings and dosing are optimal.⁷

Therefore, it is inevitable that you experiment with different settings and see what works the best for you.

For example, you may have a low pain threshold. So an intensity level that can be easily tolerated by someone else can make you feel uncomfortable.

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TENS Therapy Effectiveness

Many studies have tried to determine TENS effectiveness in different pain conditions. However, the outcome has been inconclusive with mixed results.⁵

Some of the conditions that may benefit from TENS include:³·⁵

  • Osteoarthritis
  • Fibromyalgia
  • Neuropathic pain
  • Diabetic peripheral neuropathy
  • Postoperative pain
  • Acute non-postoperative pain
  • Low back pain

Overall, the evidence suggests that TENS may be useful for a variety of pain conditions.⁵

Factors affecting TENS therapy success

TENS therapy success and effectiveness depends on several factors.
Examples are:

  • TENS unit intensity (pulse amplitude)
  • Repeated application
  • TENS unit frequency (pulse rate)
  • TENS electrode placement

► TENS unit intensity (pulse amplitude)

The intensity of TENS is critical to achieving a successful result. During TENS therapy, the pulse intensity should be adequately strong to stimulate pain relief mechanism in the body.³

Studies suggest that strong, but comfortable intensity – just below the pain threshold – can be more effective in pain relief than low intensity.³

However, not everybody can tolerate TENS higher intensities. So, high intensity could be considered according to the individual’s level of tolerance.³

► Repeated application

Repeated TENS application may produce a cumulative carryover effect. If that happens, you can feel pain relief long after the therapy session.³

At the same time, the repeated application can also cause you to develop tolerance to TENS. This can happen if TENS therapy is done with the same frequency, intensity and pulse width daily for over a week.²

Some studies suggest increasing intensity 10% daily to delay the onset of tolerance.³

Many TENS units have a modulation mode that makes stimulation patterns more irregular. This may help with delaying the tolerance as well.

► TENS unit frequency (pulse rate)

Different frequencies activate different nerve groups and pain relief mechanism in the body.
Lower frequencies seem to be more effective in managing chronic pain.

But since high-frequency TENS is more comfortable, many people start with it before moving to lower frequencies.³

One way to delay tolerance is to have the therapy with mixed frequencies. In this case, you can switch between high and low frequencies during the treatment.³

However, the high-frequency TENS is more likely to release pain than a low-frequency TENS if you are taking opioid medication. In this case, mixing frequencies may not be helpful.³

► TENS electrode placement

Placing TENS unit electrodes directly over the painful area may be optimal but is not necessary for TENS therapy. There are other alternatives for electrode placement that can be as effective.

For example, the electrodes can be placed close to the source of pain instead of on top of it. The electrodes may also be placed quite remote from the painful area or even on the opposite side of the body and still successfully manage the pain.¹

Some studies suggest that TENS therapy may be more effective if the electrodes are placed over acupoints than non-acupoints.⁵

In acupuncture therapy, acupoints are spots on the body where an acupuncture needle is inserted.

Does the size of TENS unit pads matter?

Some studies suggest that the size of electrode pads in a TENS unit may have a role in the density of electrical pulses delivered to the skin.⁷

The logic behind it is that if the electrode pad has uniform electrical conductivity, then the electric current spreads to the contact area and the current density would be inversely proportional.⁷

In other words, if one small and one large electrode pad are connected to the TENS power unit with the same settings, the person feels a greater amplitude from the smaller pad than the larger one.⁷

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TENS Therapy Safety

TENS therapy is generally considered to be safe with few side effects.⁷

However, like any other type of treatment, TENS therapy should be done with caution and according to the instruction manual that comes with the TENS device. Always consult with your doctor or healthcare provider before starting any treatment on your own to make sure it is safe and effective for you.

TENS therapy side effects

TENS side effects are few. Below are some examples:

  • You may experience an allergic skin reaction to the electrode pads.
  • It may irritate or burn the skin and may cause hypersensitivity, soreness and muscle contractions, especially if the intensity is set too high or the treatment is done for too long.

Where not to use a TENS unit

TENS unit electrodes must not be put over some parts of the body that are considered danger zones.

Examples are:

  • Eyes
  • Head
  • Throat
  • Chest
  • Tumors
  • Open wounds or broken skin
  • On the spinal column
  • Over the main arteries
  • In the mouth or internally

Who should avoid TENS

TENS therapy can cause health complications and prevent healing in some people.

For example, using TENS after an operation may cause muscle contractions that impede the healing process.

Make sure to consult with your doctor to see if TENS is safe for you.

Below are examples of people who must NOT use a TENS unit before consulting with their doctor:

  • People with suspected or diagnosed epilepsy
  • Pregnant women
  • People with cancer
  • People with implanted devices such as defibrillators and pacemakers
  • People with suspected or diagnosed heart problems
  • People who have undiagnosed pain or when the cause of pain is unknown
  • People with acute disease or infectious disease
  • People with abnormal blood pressure
  • People with an abnormal skin condition or lack of skin sensation

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Best TENS Units to Buy

There are many TENS unit models and brands in the market with various options and gimmicks.

How to choose a TENS unit

When choosing a unit, one of the most important things to pay attention to is how you can control and adjust TENS parameters. A good TENS unit gives you an option to control parameters in its setting. These parameters include pulse intensity (pulse amplitude or strength), pulse frequency (pulse rate) and pulse width (pulse duration). The range of each of these parameters is also important.

Most TENS units come with preset programs and modes. TENS parameters are often preconfigured in these modes based on common usage and application.

“I’m in pain all the time,’ I said, ‘and if I gave into it, then I’d do nothing.”

Bernard Cornwell, English author


Buy one of the below best-selling TENS units and manage your pain before it manages you.


TENS 7000 2nd Edition

Buy Now

  • This unit comes with 2 dual wires, each attached to 2 electrodes. It has 4 electrode pads in total.
  • You can adjust the intensity via two control knobs. Each knob controls 1 dual wire and 2 electrodes attached to it.
  • The unit pulse intensity (amplitude) is adjustable between 0 to 100mA
  • The frequency is adjustable between 2 to 150Hz
  • The pulse width is adjustable between 50 to 300uS with 10uS per step
  • It has 5 pre-programmed modes.
  • It uses one 9-volt battery to work.


HealthmateForever YK15AB TENS unit

Buy Now

  • This unit comes with 4 dual wires, each attached to 2 electrodes. It has 8 electrode pads in total.
  • It has 20 levels of intensity that you can adjust yourself. Each dual wire can have its own intensity set independent of others.
  • It has 15 pre-programmed modes. These modes are labeled as knee, shoulder, etc.
  • You can adjust the frequency with speed buttons.
  • It uses 3 AAA batteries to work.



Buy Now

  • This unit comes with 4 dual wires, each attached to 2 electrodes. It has 8 electrode pads in total.
  • The electrode pads have different shapes and sizes: large, medium and small.
  • It has 10 levels of adjustable intensity.
  • It has 16 pre-programmed modes.
  • This unit has a built-in rechargeable lithium battery. It comes with 1 USB cable and one AC adapter. It can be connected to a wall unit or computer USB port to charge.

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Please note that the information compiled in this article is from a variety of sources and it may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. Always seek the advice of a doctor or other qualified health providers with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. Learn more


[1] Kong, X., & Gozani, S. N. (2018). Effectiveness of fixed-site high-frequency transcutaneous electrical nerve stimulation in chronic pain: A large-scale, observational study. Journal of Pain Research, 11, 703-714. doi:10.2147/jpr.s156610

[2] Liebano, R. E., Rakel, B., Vance, C. G., Walsh, D. M., & Sluka, K. A. (2011). An investigation of the development of analgesic tolerance to TENS in humans. Pain, 152(2), 335-342. doi:10.1016/j.pain.2010.10.040

[3] Sluka, K. A., Bjordal, J. M., Marchand, S., & Rakel, B. A. (2013). What Makes Transcutaneous Electrical Nerve Stimulation Work? Making Sense of the Mixed Results in the Clinical Literature. Physical Therapy, 93(10), 1397-1402. doi:10.2522/ptj.20120281

[4] Page, M. J., Green, S., Mrocki, M. A., Surace, S. J., Deitch, J., Mcbain, B., . . . Buchbinder, R. (2016). Electrotherapy modalities for rotator cuff disease. Cochrane Database of Systematic Reviews, (6), CD012225. doi:10.1002/14651858.cd012225

[5] Vance, C. G., Dailey, D. L., Rakel, B. A., & Sluka, K. A. (2014). Using TENS for pain control: The state of the evidence. Pain Management, 4(3), 197-209. doi:10.2217/pmt.14.13

[6] DeSantana, J. M., Walsh, D. M., Vance, C., Rakel, B. A., & Sluka, K. A. (2008). Effectiveness of Transcutaneous Electrical Nerve Stimulation for Treatment of Hyperalgesia and Pain. Current Rheumatology Reports, 10(6), 492–499. PMCID: PMC2746624, NIHMSID: NIHMS130619, PMID: 19007541

[7] Neto, M. L., Maciel, L. Y., Cruz, K. M., Filho, V. J., Bonjardim, L. R., & Desantana, J. M. (2017). Does electrode placement influence tens-induced antihyperalgesia in experimental inflammatory pain model? Brazilian Journal of Physical Therapy, 21(2), 92-99. doi:10.1016/j.bjpt.2017.03.003