TENS and pain relief - Find out more

What is Pain?

When we feel pain it is the body’s process of informing us that something is wrong. To feel pain is important, without this feeling abnormal conditions may go undetected, creating damage or injury to critical parts of the body.

Although pain is essential in warning our body of trauma or malfunction, nature may have gone too far in its design. Continued long-term chronic pain has no useful value apart from its importance in diagnosis.

Pain begins when a coded signal travels to the brain where it is decoded, and analysed. The pain message travels from the injured area of the body along small diameter nerves leading to the spinal cord. At this point the message is switched to a different kind of nerve that travels up the spinal cord to the brain area. The brain then analyses the pain message, refers it back and the pain is felt.

Quick Links:

What is TENS ?
History of TENS
How Does TENS Work?
Applications
Contra Indications

What is TENS?

Transcutaneous Electrical Nerve Stimulation (TENS) uses a small battery operated unit to provide a non-invasive, drug free method of controlling acute and principally long term intractable pain. It can also be used as an adjunctive treatment in the management of post surgical traumatic pain problems.

Mild electrical impulses are transmuted through the skin via surface electrodes to modify the body’s pain perception. TENS does not cure problematic physiological conditions; it only helps to control the pain perception. TENS will not work for every user However Physiotherapists and Doctors throughout the world prescribe it extensively and it is generally seen to work for the majority of users.

There are millions of small nerve fibres throughout the body and it only requires a few impulses to produce chronic pain. In addition to small fibres, which allow the sensation of pain to be felt, the body is also made up of larger diameter nerve fibres. These larger nerve fibres transmit less unpleasant sensations such as touch or warmth, assisting us to form an impression of our environment. Stimulating the larger nerve fibres using it may have the effect of inhibiting the transmission of pain along the smaller nerve fibres to the spinal cord [known as the ‘Pain Gate Theory’].

History of TENS

The gate control theory of pain, which was developed by Melzack and Wall (1965) postulates that pain impulses arrive at a gate, which is thought to be the substantia gelatinosa.  When the gate is open pain impulses can pass easily, when the gate is partially open only some pain impulses can pass and when the gates is closed no pain impulses are able to pass.  It is suggested that the position of the gate depends upon the degree of large or small fiber firing.  When large fibers firing predominates, the gate closes so that no impulses can pass through, where as when small fiber predominates, the pain message can be transmitted.

According to McCaffery (1983), the gate control theory is based on complex physiology, which brings many aspects of it into question.  Nevertheless, as Carey (1985) indicates, even though some aspects are controversial, this is still one of the most widely accepted theories of pain impulse transmission.

How Does TENS Work?

Low frequency stimulation encourages the release of our bodies natural pain relief substances commonly known as endorphins, which can be up to two hundred times more potent than morphine.  Studies indicate that endorphin related pain relief can often last for periods which extend considerably beyond the time of stimulus.  Thus, even after the TENS unit is switched off, pain relief can be sustained.  Latest research indicates that in many conditions, pain conducting nerves can be programmed and may continue to transmit pain even after the cause has been eliminated.  In these cases TENS will reduce the excitability of pain nerves, breaking the pain cycle and restoring normal balance.

Tortora and Anagnistakas (1984) divided pain into two types: somatic pain arising from the stimulation of receptors in the skin, muscle joints and tendons and visceral pain arising from the stimulation of receptors in the skin, muscle joints and tendons and visceral pain arising from the stimulation of receptors in the viscera.  In general, pain receptors are classified according to location (Carey, 1985).  Receptors that respond to injury or noxious stimuli are termed nociceptors and are sensitive to thermal, electrical, mechanical, chemical and painful stimuli.  Each receptor is connected to a nerve and when the receptor is connected to a nerve is activated, firing an electrical impulse along its length (Hoskins and Welchew 1985).  Nerves can also be categorised according to their diameter and whether or not a myelin sheath is present.

Fordham (1986) suggested that three types of nerves are concerned with the transmission of pain.

1. A beta fibers, which have a large diameter and are myelinated.

2. A delta fibers, which have small diameters and also have myelinated sheaths.

3. C fibers, which have small diameters and slow conduction rate and are generally involved with the transmission of dull, aching sensations (Carey 1985).

Nerves with a large diameter conduct impulses faster than those with a small diameter (Hoskins and Welchew 1985).  The presence of a myelin sheath encourages nerve impulses to pass even faster.

TENS Applications

There are many TENS units on the market and are widely used through out the world very successfully to help reduce or keep pain under control.  TENS is being used for a variety of conditions of which a few are detailed on this page.  

• Arthritis
• Phantom limb pain following amputation
• Lumbago
• Post operative pain
• Sports injury
• Amputation
• Skeletal pains
• Whiplash
• Rheumatoid and osteo arthritis
• Period pain
• Pain associated with chronic fatigue syndrome
• Neuralgia
• Back pain
• Most muscle pains
• Cancer pain

Contra Indications of TENS

• It is inadvisable to use TENS if  demand type pacemaker is fitted.
• It is not advisable to drive a vehicle or operate dangerous machinery whilst receiving TENS stimulation.
• The safety of TENS during pregnancy has not been established.
• Care must be used when treating to avoid the immediate vicinity of the richly innervated cartoid sinus.
• The user should only use the device as prescribed.
• Should not be used for undiagnosed pain.
• Skin irritation from the treatment itself does not occur.  However, certain skin types do react to the glue on the electrodes and, therefore, users should use hypoallergenic brands.
• Unit should not be immersed in liquid substances.