How Does A TENS Unit Work?

TENS machines are used by hundreds of thousands of pain sufferers all over the world for the relief of many types of physical pain, from back to knee to neck pain. 

Some of the most common uses for TENS treatment include acute and chronic pain, post-operative incisions and post-surgical pain, labor, and delivery, migraine and tension headaches, acute pain from sports and other injuries, arthritis, chronic pain from tendentious and bursitis, pain relegated to cancer therapy, and wound management. 

The term TENS is actually an acronym meaning Transcutaneous Electrical Nerve Stimulation unit. Some patients find relief by using a TENS unit, which when applied to the skin’s surface, delivers a gentle electric current and relieves the pain. In this modality, large surface electrodes are affixed to the skin and stimulate the underlying nerves that supply the painful area. Under the patient’s control, the flow of current is gradually increased until a tingling is felt. The stimulus is provided by a small control box, with the patient is in complete control of administrating the current after a preliminary training period. 

There are two major pain theories to explain how a TENS unit works to relieve, decrease, or eliminate pain. The major theory is called The Gate Control Theory and is considered by most doctors and therapists to be the most advanced explanation. The gate-control theory suggests that there’s a neural mechanism in the spinal cord that acts as a kind of gate, shutting down or opening up the flow of signals from the periphery to the brain. Whether the gate is open, closed, or partially closed depends on what sort of signal it receives from the brain to change the perception of pain in the user’s body. These frequencies can hinder the transmission of pain messages at the spinal cord level and can help block their transmission to the brain.

A second theory is called The Endorphin Release, which suggests that electrical impulses stimulate the production of endorphins and enkephalins in the body. These naturally produced morphine-like substances will block pain messages from reaching the brain, in a similar fashion to conventional drug therapy, but without the risk of dependence or chance of other side effects.

Clinical researchers and doctors who work with chronic pain all report a consistent finding of body pain. It is almost impossible to have pain, without having either tight muscles or muscle spasm. The more physically tense a person with chronic pain becomes, then the more pain they have been shown to occur. This is why research, clinical trials, and all types of doctors have recommended using a TENS unit for all degrees of pain. Repeated studies have shown to relax the muscles around an injury and bring blood flow to the area, allows the body to become less tense, and muscle spasms can disappear or be reduced.

TENS Units typically have three different mode settings. They are usually referred to as Normal, Burst, and Modulation. The normal setting is recommended for inexperienced users. This mode is most commonly used to relieve acute pain. The burst setting is perfect for individuals who suffer from chronic pain, as TENS units usually send a burst of pain-relieving power. The Modulation setting is useful for both acute and chronic pain. When in Modulation mode, the unit varies between a few different settings. Pain relief occurs at various frequencies and the pulse rate is considered to be the number of electrical pulses a person feels in one second. These frequencies are measured in Hertz. For those who suffer from acute pain should set the frequency to be between 80 and 120 Hertz. For Muscle Stimulation, then 35-50 Hertz are the recommended values. For Chronic Pain, between 2 and 10 Hertz are the recommended settings. 

The width of the pulse or periods when the current is sent can also be modified and controlled. In general, pain relief occurs with low/mid time periods, but a longer pulse width may be needed for greater muscle contraction. The recommended settings for pulse width are: 175 to 200uS (Pulse widths are measured in milliseconds)

How Long Can You Use a TENS Unit? While the settings differ, depending on your needs and preferences, but generally here’s how long a TENS unit can be used.  For Acute Pain, it is suggested between 20 and 60-minute sessions, each up to four times a day. For Chronic Pain, it is best to limit sessions to 20-30 minutes each and no more than to 5 times a week. Work with your doctor or clinician to find what the right balance of time and use makes sense for your individual circumstances. 

TENS Electrodes are usually positioned directly on the area that needs to be treated, but using an “unconventional” placement can sometimes yield even better results. One example is that you may feel pain in the central part of your neck, but you should place the electrodes on either side of the neck.

Even though TENS Units are considered to be perfectly safe, FDA approved and often sold over the counter, they still need to be used in the correct way. Never place an electrode in the following places:

  • On or near your eyes
  • Through the chest
  • Across a cardiac pacemaker
  • On the front of your neck
  • Directly on an open wound (you can place it around wounds instead)
  • Directly over a malignant tumor
  • Directly on the spinal column (you can place it on the sides of the column, though)
  • Internally or on mucus membranes  (unless you own a specialized unit)
  • On areas of decreased sensation
  • On areas of active infection
  • If you have been diagnosed with either epilepsy or dementia.  

When used as directed, TENS is a considered a safe, non-invasive, drug-free tool for pain management. A TENS unit is used to offer a better quality of life for people with pain instead of sustained drug therapy with the chance of side effects.