Alternative therapiesBack PainChronic PainJoint Pain

How Does A TENS Unit Work?

In this post I am going to try to explain how a TENS (Transcutaneous Electrical Nerve Stimulation) unit works. So after reading this post any person should be able to use this very effective form of treatment for pain.  This form of pain management is most effective for pain that is recent or acute, comes from muscles-ligaments-tendons-joints, and has an obvious diagnosis.

Recent estimates are that 100 million Americans suffer from some type of pain syndrome. Those estimates include both acute and chronic pain.  The physiology of acute pain is different from chronic pain.  Because of this, the effectiveness of TENS therapy varies.

Acute pain is any pain that lasts for less than 3 months.  Chronic pain evokes different nerve conduction at about the 3 month mark when the pain has occurred daily for 3 months or longer.

The Basics Of a TENS UNIT

A TENS unit will consist of the generator/mini-computer (g/m), attachment wires, skin attachment pads, and an electrical source (usually batteries).  Some devices are quite small and can be worn discretely under clothing.

The g/m usually has a number of different settings that can be dialed into it which varies the intensity and the frequency of the electrical signal that is being sent to the skin attachment pads.  It is essential that every user of a TENS unit become familiar with the specific settings for their unit by thoroughly reading the manual for their machine (this is almost never done by the patient or Doctor).

While I was in medical practice I met too many patients who were using (or trying to use) a TENS unit that they were unfamiliar with.  Whether they had not read the manual, or couldn’t understand the manual, or were never shown the basics by the person who gave them the device, I do not know.

When a TENS unit is turned on there will be a need to dial in certain parameters.  At the most basic level this will be the intensity and frequency of the electrical signal to the skin pads.  This is essentially an electrical “prescription” for the type of pain the TENS is supposed to be treating.

Medical equipment for Physical therapy

Intensity is the amount or volume of electricity that will be pushed through the wires.  The more volume the more effect at any given frequency.  Think of it as the “size of a meal.”

Frequency is the number of waves that pass over a point in time that will be pushed through the wires.  With a higher frequency the waves are “tighter”.  A lower frequency wave is “looser” or more broad.  The shape effects different places in your nervous system differently.  Think of it as the “taste of a meal.”

Everyone knows that a gourmet meal that is small will not satisfy your hunger.  Also, a tasteless meal that is large is boring and doesn’t satisfy either.  A well prescribed TENS will have just the right intensity and frequency for the pain being treated.  This is very individualized for each person.  No single electrical prescription suffices for everyone.

This is not as easy to determine as you may think…which brings us to a short discussion on the physiology of pain.

A Brief Review Of Pain Physiology

pain pathways

The nervous system of a human being is made up of 100 billion nerve cells.  Each cell has thousands of connections which respond to internal and external stimuli.  The system is ever changing, dynamic, and involved in every organ system of the body.

Each human being (even identical twins) has a totally unique nervous system from every other human being.  The way a person’s nervous system responds to painful stimuli is very individualized and changeable.

All of this “uniqueness” effects the way a TENS unit works.  Generally, the frequency and intensity of the electrical signals effect different areas of the nervous system differently.

Furthermore, placing the skin pads of a TENS unit on one side of the body can actually reduce pain on the other side of the body where there are no skin pads.  The best effect for pain relief occurs when the pads are placed directly on the skin over an injured area.

The TENS unit turns on and turns off nerve signally in the base of the brain, spinal cord, and peripheral nerves that effects the level of pain a person feels.  Perception, transmission, generation, and inhibition of pain are all effected.

Just as a person can develop tolerance to a pain medication, tolerance to TENS therapy can develop.  This brings us to the next section…

What Does It Mean When You Build a “Tolerance” To Your TENS UNIT?

The human body has an incredible ability to adapt.  This adaptation causes medications that once worked to lose their effectiveness and causes TENS unit therapy to diminish over time.

In fact, continuous daily use of a TENS unit causes its effectiveness to diminish so that by day 10 the unit is no longer effective if the unit has been maintained at the same intensity and frequency.  There are a few adjustments that can help.

By varying the frequency and intensity of the electrical signal the tolerance can be slowed, but not eliminated.  By varying the location and number of skin pads, tolerance can also be delayed.

Electrodes of tens device on back muscle

What Can a TENS UNIT Be Used For?

The following diagram shows what a TENS unit can be used for and the placement of the electrodes:

tens electrode placement
When Should a TENS UNIT Be Used With Caution?

As a TENS unit uses an electrical current, every implanted electrical  device (a pacemaker for instance) is potentially vulnerable to being effected by it. Extreme caution should be exercised under the following circumstances:

  • When a patient has a pacemaker
  • When a patient has an embedded deep electrical stimulator device (such as for depression or for pain)
  • When a patient is pregnant (for fear of the induction of labor)
  • When placing the electrodes on the face near their brain (for fear of seizure induction)

A TENS UNIT Video For More Instruction

I have included a short digital video to explain the application of a TENS unit a bit further:


I have presented a brief review of the TENS unit that can be applied practically for pain relief of many painful conditions.  This post is not a medical recommendation for the use of TENS therapy nor an endorsement for any specific device.

 There are 3  major limitations in the use of a TENS unit:

  1. You must learn the technical complexities of the unit.  There is a major learning curve with the proper use of this type of device.  It will require a substantial amount of reading (the manual must be thoroughly understood).
  2. You will have to “experiment” with the settings to obtain the best relief.  The manual will give you a starting frequency and intensity.  From there you will have to identify your individual “electrical prescription” for best pain relief.
  3. You will develop a rapid tolerance to your “electrical prescription” so that it will have to be adjusted every 10 days (or sooner).

Before using this very effective pain treatment, a thorough history and physical, diagnostic workup, and diagnosis by a primary care practitioner should be accomplished.

If you have further questions, please comment below. I would love to hear from you. I will get back to you promptly.

Wishing you joy and healing.

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