Updated: Sep 17, 2018
TENS: Transcutaneous electrical nerve stimulation
What is electrotherapy, anyway?
Humanity has always been fascinated with electricity, picture Zeus, father of the gods and of men throwing thunderbolts – the ultimate weapon – down from mount Olympus. Electrotherapy began with the ancient Romans, a full 1800 years before Edison and Tesla harnessed electricity to be used as a utility. Scribonius Largus, who served as the court physician to the mighty Roman Emperor Claudius, reported in the year 46 A.D. that one could use the electric ray, a fish that emits an electrical pulse when touched, to treat a variety of medical conditions.:
“To immediately remove and permanently cure a headache, however long-lasting and intolerable, a live black torpedo [electric ray] is put on the place which is in pain, until the pain ceases and the part grows numb” – Scribonius Largus in his Compositiones Medicamentorum (46AD)
These uses were also known to the ancient Greeks, Aristotle and Plato referred to the fish in their works. In fact, the ancient Greek word for the electric ray fish is “narka”, which is the etymological source of our word “narcotic” – a pain killing substance. The Greeks, clearly, were aware of the potential of electricity (an anachronism to be sure, but they understood its effects) to treat pain. The Greeks used them to variously numb the pain of childbirth, operations and to treat epilepsy.
The use of the electric ray (or torpedo fish) was a very early means of targeted, intentional TENS therapy. Fortunately, today we can enjoy the benefits of electrical therapy in a slightly more refined, and safe way than to place marine life on one’s body. The modern TENS device is safe, effective, and can be used to help a variety of conditions.
How does a TENS device work?
Transcutaneous electrical nerve stimulation uses an electrical current to stimulate the nerves in the skin. The devices is connected to the skin by two or more electrodes which transmit the electrical current, reaching the nerves. A typical, consumer-grade TENS unit is able to modulate pulse width, frequency, and intensity for different uses. TENS is usually either applied at a high frequency above 50 Hz, with a low intensity that doesn’t cause muscle contraction, or at a low frequency, less than 10 Hz, at an intensity that causes motor contraction (i.e. muscle movement).
Electrical impulses sent by TENS devices essentially crowd out other signals sent from the same nerve to the brain. In order for someone to feel pain, nerves at the site of the pain transmit a signal to the spinal cord, which brings the signal to the brain, where it is processed and experienced as the negative sensation we call pain. TENS devices work, in part, by interfering with this signaling process. Their electrical impulses reach the nerves like pain signals do. Nerves only have so much “bandwidth” to transmit a signal, so if the nerves are busy with the TENS signal, there is no room for the pain signal to be transmitted to the brain.
TENS affect both central and peripheral mechanisms in order to reduce pain perception. In the central nervous system, TENS activates opioid, serotonin and muscarinic receptors. Peripherally, opioid and alpha-2 noradrenergic receptors are involved – similar to how many pain medications work! The opioid system is classically considered to be the key to pain control, and the most effective pain killing drugs directly target it. TENS also is able to activate this system, and is not associated with the potential for the same side effects as narcotics, such as addiction/dependence, withdrawal symptoms, altered mental status, etc. These facts make TENS an important alternative therapy to be considered for anyone facing pain – there are other options than dangerous drugs.
Uses for TENS therapy:
TENS therapy can be extremely useful for the reduction of both acute and chronic pain. This includes low back pain, neck pain, joint pain of all kinds, etc. It is particularly effective for pain involving muscle spasms. TENS has also shown effectiveness in the treatment of carpal tunnel syndrome. A study was done involving a brain scan (MRI) of patients with carpal tunnel and it showed that there were significantly fewer activations of the brain in areas associated with pain when a TENS device was used than compared to a placebo.
TENS units have also shown promise in the treatment of labor pain associated with childbirth. Orofacial pain is also effectively treated with electrical nerve stimulation, with application in dentistry as well as temporomandibular joint dysfunction (TMD) where there are issues with jaw stiffness, pain, and clicking noises in the joint.
A fundamental use for TENS therapy is in treating hyperalgesia, or overactive nerves. Hyperalgesia is a condition where the perception of pain is heightened – nerves perceive things as more painful than they should be, which can lead to chronic pain easily. TENS devices effectively desensitize nerves by exposing them to an excess of non-painful stimuli, which over time tends to normalize nerve function and brain sensitivity to pain. This makes it an excellent choice for those suffering from chronic pain conditions. 
Safety of TENS devices:
TENS therapy with modern consumer devices is extraordinarily safe and effective for treatment of a variety of illnesses, however there are some precautions that should be followed. Do not use a TENS device in the following locations of the body:
· Over the eyes (due to risk of increased ocular pressure)
· On the front of the neck (possibility of hypotension via activation of vasovagal response)
· Through the chest use posterior and anterior electrode placement (e.g. one pad on chest, other on back, both on left side of body, as this could theoretically interfere with heart rhythm – you don’t want to defibrillate yourself unless you have to)
· Over broken skin
· Over the location of a tumor (some studies show electricity promotes cell growth)
· Directly over the spinal column
Over 70,000 Americans died last year of opioid overdose, the highest number in history. Many of those people were first prescribed opioids by a doctor for a legitimate medical condition. There is a clear and pressing need for alternative methods of pain relief beyond painkiller drugs in this country. Transcutaneous electrical nerve stimulation is a great option that should be considered in lieu of, or as a complement to opioid painkiller drugs. It is safe, non-addictive and effective for many people for treatment of pain ranging from gym-soreness to chronic low back pain.
 Johnson M, Martinson M (2007). "Efficacy of electrical nerve stimulation for chronic musculoskeletal pain: A meta-analysis of randomized controlled trials". Pain. 130 (1–2): 157–165. doi:10.1016/j.pain.2007.02.007. PMID 17383095.
 Kara M, Ozçakar L, Gökçay D, Ozçelik E, Yörübulut M, Güneri S, Kaymak B, Akinci A, Cetin A (2010). "Quantification of the Effects of Transcutaneous Electrical Nerve Stimulation with Functional Magnetic Resonance Imaging: A Double-Blind Randomized Placebo-Controlled Study". Archives of Physical Medicine and Rehabilitation. 91 (8): 1160–1165. doi:10.1016/j.apmr.2010.04.023. PMID 20684895
 Differences in waveform characteristics have no effect on the anti-hyperalgesia produced by transcutaneous electrical nerve stimulation (TENS) in rats with joint inflammation.
Hingne PM, Sluka KA
J Pain. 2007 Mar; 8(3):251-5.