TENS, or Transcutaneous Electrical Nerve Stimulation, is a type of pain therapy that uses skin surface electrodes to deliver low voltage electric impulses that stimulate the nerves in your body and reduce the sensation of pain. TENS is most commonly delivered from small, hand held, battery powered devices called “TENS units”. In most countries, TENS units can be purchased “over the counter”, without the need of a medical prescription. TENS units are used to treat symptoms such as back pain, postoperative pain, period pain and sports injuries. TENS units help provide a better quality of life for people with pain.

TENS units have different adjustable settings to control the intensity of the electrical impulses, and also the duration of each pulse.

A brief history of TENS therapy

The concept of electric nerve stimulation as a therapeutic medical application is not a recent discovery. For example, the knowledge of electricity dates back to Ancient Egypt – ancient Egyptians were already with the Nile catfish’s ability to generate electricity. But the first use of electrical stimulation for pain control was actually done in ancient Rome, by an ancient Roman physician called Scribonius Largus. In his works, he described how placing a torpedo fish on a patient’s head could relieve headache. Largus even used a torpedo fish to treat Gout. However, it wasn’t until the 19^th century that medical electric devices were used for pain control and cancer cures.  These devices were not portable, and had a very limited control over the electrical pulses.

The first modern, portable TENS unit was patented in the United States in 1974. And the development of TENS units as we know them today is credited to C. Norman Shealy, an American Neurosurgeon. Actually, TENS units were used to test the tolerance of chronic pain patients to electrical stimulation before implantation of electrodes in the spinal cord dorsal column. However, many of the patients said they received so much relief from the TENS itself that they didn’t come back for the implant.  TENS therapy became more and more popular, and many medical companies began manufacturing TENS units after that.

Because TENS is a noninvasive method for relieving pain, thousands of people use them and a lot of health professionals recommend TENS as a drug-free method for pain management.

How does a TENS unit work?

A TENS unit delivers small electrical impulses to electrode pads that are placed directly on your skin. These impulses travel through the skin and stimulate the sensory nerves, and by so doing, activate specific natural pain relief mechanisms. The theory behind TENS focuses on two primary principles:

1-Gate control theory:  The small electrical impulses sent by TENS disrupt the pain cycle by blocking pain receptors from reaching the brain.  Although the science behind TENS isn’t completely known, it is accepted that this mechanism involves activation (excitation) of the A beta Aβ) sensory fibers, and by doing so, reduces the transmission of the noxious stimulus from the ‘c’ fibers, through the spinal cord and hence on to the higher centers.

2- Stimulating Endorphin release: Endorphin is the body’s feel good substance.

Because TENS works differently from one person to another, TENS units have a few parameters and settings to control the current intensity, pulse frequency, and pulse width. The electrical current used in most TENS units that are available on the market is usually between 1 and 50mA, which is sufficient to target the sensory nerves. Most TENS machine can deliver between 2 – 150 pulse per second (Hz), and each pulse lasts between 50 to 250 micro second.

Here is a video that explains how TENS units work for pain:

Credit: University of IOWA health Care

TENS Modes

• Traditional TENS (Hi TENS, Normal TENS): This TENS mode uses a relatively high frequency (between 80 and 130Hz) and relatively short duration pulses (low pulse width).
• Acupuncture TENS (Lo TENS, AcuTENS): In this mode, a lower frequency stimulation (2-5Hz) with wider pulses is used.
• Brief Intense TENS: This mode employs a high pulse frequency (80 to 130Hz) and a high pulse width.
• Burst Mode TENS : This mode is similar to traditional TENS, but when Burst mode is switched in, the stimulation is interrupted at a rate of 2 to 3 bursts per second.
• Modulation Mode TENS : When this mode is switched on, the pulses delivered by the TENS unit have a less regular pattern. This mode can be used to reduce the accommodation effects that some patients may notice.

How to use a TENS unit

Before using a TENS unit, it is recommended that you check with your physician whether TENS therapy is right for you. And like all medical devices, so you should always make sure you carefully read the manufacturer’s instructions.

Here are 7 rules and tips you should follow when using a TENS unit:

1. To ensure effective stimulation, the electrode pads should be placed on the painful areas of your body. The electrodes should not be placed on the sinus nerves, temples, throat, eyes, spine, or mouth. Also, the pads shouldn’t be placed on the heart or on swollen or inflamed areas.
2. Always start with the lowest intensity
3. According to your body’s response to the treatment, you can gradually increase the intensity if necessary.
4. The pads have a gel that make them attach to the skin, and to extend the electrode pads’ lifespan, it is recommended  that you clean your skin before you start and put them back in the storage bags when you are done. You should also avoid touching the gel on the patches.
5. Most TENS units come with a built-in rechargeable battery, so make sure the battery is fully charged before you start using the device. If the battery level is very low, do not use the TENS unit, you should always change or recharge the batteries first.
6.  After using the TENS unit, always put the protective films on the pads’ adhesive surface and put them back in the pad holder. You should also remove the lead wires and put them in the box.
7. Store the unit and wires in a cool, dry place when you are not using it.