A TENS machine provides an easy to use and drug free method of electronic pain relief.
TENS is an abbreviation of
Transcutaneous Electrical Nerve Stimulation. Transcutaneous means "across the skin". In simple terms, a TENS unit stimulates your nerves via an electrical current through your skin.
The TENS unit is usually a small battery operated box which produces pain relieving electrical pulses. Either two (single channel) or four (dual channel) self-adhesive electrodes are applied to the skin and attached to the TENS unit with lead wires.
Modified electrical pulses are then passed from the TENS unit, via the lead wires and electrodes, to the nerves which lie underneath the skin surface.
The electrodes are normally positioned over the area of pain but other more advanced applications may often prove better. Your physiotherapist is an expert in the application of TENS. If you are in doubt, please ask your local physiotherapist for specific advice to assist your pain relief via TENS.
For specific advice on TENS electrode placements and TENS machine settings you are advised to seek the professional assistance of a health professional with expertise in the use of TENS machines such as your local physiotherapist.
What are the Benefits of using a TENS Machine?
TENS does not involve the use of drugs.
TENS is a strong electronic pain reliever.
TENS machines are powerful even though it is battery powered.
TENS machines are portable because they are battery powered. You can take your TENS anywhere.
TENS is commonly used as an alternative to epidurals and other drugs during childbirth.
How Does a TENS Machine Relieve Your Pain?
A number of systematic reviews or meta-analyses have confirmed TENS to be effective for postoperative pain, osteoarthritis, and chronic musculoskeletal pain.
Scientific Explanation of How TENS Relieves Your Pain.
Scientific studies show that high and low frequency TENS produce their effects by activation of opioid receptors in the central nervous system.
Specifically, high frequency TENS activates delta-opioid receptors both in the spinal cord and supraspinally (in the medulla) while low frequency TENS activates beta-opioid receptors both in the spinal cord and supraspinally.
High frequency TENS also reduces excitation of central neurons that transmit nociceptive information, reduces release of excitatory neurotransmitters (glutamate) and increases the release of inhibitory neurotransmitters (GABA) in the spinal cord, and activates muscarinic receptors centrally to produce analgesia (in effect, temporarily blocking the pain gate).
Low frequency TENS also releases serotonin and activates serotonin receptors in the spinal cord, releases GABA, and activates muscarinic receptors to reduce excitability of nociceptive neurons in the spinal cord.
A TENS machine produces millions of tiny electrical impulses, which enter your body via electrodes placed on the skin near or over the painful region. These fast electrical impulses override the slower pain impulses and travel quickly along your nerves to your spinal cord and up to your brain.
Your brain is immediately bombarded by millions of pleasant electrical impulses. Your pain signals continue to be sent to your brain but travel along much slower (smaller diameter) nerve fibres. Since your brain can only interpret a limited amount of information, the pain signals are easily outnumbered by the pleasant high-speed TENS stimulation. This leads to pain relief and is known as the Gate Pain Control Theory.
The Gate Pain Control Theory was initially proposed in 1965 by Melzack and Wall based on the fact that small diameter nerve fibres carry pain stimuli through a 'gate mechanism' but larger diameter nerve fibres going through the same gate can inhibit the transmission of the smaller nerves carrying the pain signal.
It is generally recognised that the 'Pain Gate' can be shut by stimulating nerves responsible for carrying the touch signal (mechanoreceptors), which enables the relief of pain through massage techniques, rubbing, and also the application of tens machines, wheat bags and ice packs.
Why Does Rubbing Your Skin Help to Ease Pain?
"Pain Gating" is very simply described by using the example of when you "bump your elbow", and then rub it to ease the pain. When your elbow is bumped, pain messages travel to your brain. Here the messages are interpreted as "Pain". Rubbing this same elbow vigorously will stimulate an abundance of new "non-painful" messages to travel to the brain.
Luckily, your brain can only interpret a limited amount of information. If the "rubbing" sensations outnumber the painful "bump" sensations, the brain will interpret the sensations as being from the pain-free rubbing source rather than the painful bump. In other words, the rubbing sensations have 'bombarded the gate', so painful messages cannot get through.
We all know from personal experience, the faster we rub our bumped elbow, the better the results. Your TENS works in just the same way ... it's just rubs you via an electrical stimulation instead. Plus, it doesn't get as tired!
When using TENS to 'close the gate' we use Continuous (or Conventional) Tens Mode. Continuous TENS mode produces a gentle and pleasant 'tingling' under and between the electrodes. The 'tingle' sensation helps to block the pain by closing the 'pain gate' and slowing down the painful nerve signals - this produces analgesia (numbness) in the painful area that can last for a few hours.
TENS Machines Stimulate an Endorphin & Serotonin Release
Pain can also be relieved by stimulating the release of endogenous opioids (endorphins, enkephalins, and dynorphins), which are pain-relieving chemicals. Opioids are naturally occurring hormones in the body. They are released in response to an injury or physical stress to reduce your pain and promote a feeling of wellbeing.
Opioids have a similar chemical structure to Morphine, which explains their strong painkilling effects.
Serotonin is also found in the central nervous system (CNS). Serotonin is a well-known contributor to feelings of well-being; it is known as a "happiness hormone" despite not actually being a hormone. Serotonin is synthesized in serotonergic neurons in the CNS where it has various functions. Modulation of serotonin at synapses is thought to be a major action of several classes of pharmacological antidepressants.
Serotonin is also a growth factor for some types of cells, which may give it a role in wound healing.
Acupuncture and low frequency TENS machines stimulate the release of endogenous opioids and serotonin. The opioids then inhibit the transmission of pain signals in the substantia gelatinosa part of the spinal cord - what is often referred to as the spinal root part of the nerve.
When using TENS to help activate opioids release we use a low frequency Burst Tens Mode. Burst mode produces a rhythmic pulse which should be strong enough to produce a 'twitch' in the muscles underneath the electrodes. This muscle 'twitch' helps to release the opioids and also helps the pain 'switches' in the brain to be activated through muscular and reflex activity.
What Gives You a Natural High?
A great example of endorphin release is the natural 'high' that runners and other athletes experience after 30 minutes of sustained exercise. Much like exercise, the endorphin release stimulated by the TENS may take up to 30 minutes or more to take a noticeable effect.
The "feel good" effect may last several hours before endorphin levels in the body need to be increased again.
Where NOT to Use Your TENS Machine
TENS or EMS electrodes should NEVER be placed:
Across your eyes (intraocular pressure) or brain
On the front of your neck due to the risk of acute hypotension (through a vasovagal reflex) or even a laryngospasm
Through the chest (using a front and rear of chest wall electrode positions). Either side of your spinal column is permitted.
Across an artificial cardiac pacemaker (or other indwelling stimulator, implantable cardioverter-defibrillators (ICDs)
, including across its leads) due to risk of interference and failure of the implanted device. Serious accidents have been recorded in cases when this principle was not observed.
On open wounds or broken skin areas (although it can be placed around wounds.
Over a malignant tumour (based on experiments where electricity promotes cell growth).
Directly over the spinal column (although it can be placed either side of your spinal column).
Internally, except for specific applications of dental, vaginal, and anal stimulation that employ specialised TENS units.
On areas of numb skin/decreased sensation TENS should be used with caution because it's likely less effective due to nerve damage. It may also cause skin irritation due to the inability to feel currents until they are too high.
Areas of Infection. There's an unknown level of risk when placing electrodes over an infection (possible spreading due to muscle contractions). Cross contamination with the electrodes themselves is of greater concern.
How to Choose the Best TENS Machine for Your Needs