It is one of the methods of electrical stimulation whose primary aim is to provide a degree of symptomatic pain relief by exciting sensory nerves. TENS units work by delivering small electrical impulses through electrodes that have adhesive pads to attach them to a person's skin. These electrical impulses flood the nervous system, reducing its ability to transmit pain signals to the spinal cord and brain.
It is broadly categorized into 3 types:

• Conventional TENS (HIGH): It involves the application of low-intensity / high-frequency current to produce a strong but comfortable sensation, Its duration is 30 min.
• Acupuncture-like TENS (LOW): It involves the application of high-intensity / low-frequency current over muscles or acupuncture points to produce a strong but comfortable sensation. Its duration is less than 20 min.
• Brief Intense TENS: It involves the application of high-intensity / high-frequency current. It lasts for not more than 5 minutes.

Pain modulation:For pain to be perceived there is usually a chain whereby peripheral receptors are stimulated by a noxious physical or chemical agent and this stimulus is carried by peripheral nerves to the spinal cord, up to the cord, through the brainstem and so to the cerebral cortex, where the pain is appreciated by the conscious level. This route necessarily involves a number of synapses and the inhibition of impulses on their route to the cortex is the mechanism whereby pain can be modulated.
Nociceptive nerve endings may be stimulated by the chemicals released by tissue injury or accumulated as a result of metabolic activity, and thus creating an electrical potential. The degree of stimulation produced is governed by the number of chemicals present. It is postulated that the removal of these chemicals from the area may help reduce the level of nociceptive stimulation and thus the physiotherapeutic agents (ice and heat) affecting the circulation may help achieve this. The nociceptive stimulus is carried to the cord along with either a slow-conducing, non-myelinated C fiber or a faster-myelinated Ad (delta) fiber. Both will eventually enter the cord via the posterior route. It is postulated that as both of these fibers have a maximum frequency at which they can conduct that if a higher frequency of stimulation is applied, a physiological block o conduction might occur. TENS produces this required frequency and so has this effect.

A TENS unit has controls that allow people to administer an appropriate level of pain relief. It can be achieved by altering the intensity, frequency, and duration of the impulse. It may help in treating the following symptoms:

• Chronic pain syndromes
• Period Pain
• Labor Pain
• Postoperative Pain
• Joint Pain
• Muscular pain
• Ligamentous pain
• Tendinitis pain
• Neck and Back Pain

It may also alleviate the pain that results from the following:

• Endometriosis
• Arthritis
• Sports Injury
• Multiple Sclerosis
• Fibromyalgia
• Myofascial trigger points
• Painful Diabetic Neuropathy
• Spinal Cord Injury
• Amputation

It is safe for most people to use a TENS unit, with usually no side effects but,

• The electrical impulse of a TENS may cause a buzzing, tingling, or prickling sensation, which might be uncomfortable for some.
• Some people may be allergic to adhesive pads. Anyone who experiences skin redness and irritation can switch to hypoallergenic ones.
• Electrodes should never be placed on the front of the neck as it may lower blood pressure or Over the eyes, as it may cause injury.

Although it is safe for most people, experts recommend that some groups of people must avoid the TENS treatment unless the doctor advises its use.
The above recommendation applies to the following people:

• Pregnant Women: She should avoid using it in the abdominal and pelvis regions
• People with Epilepsy: Applying electrodes to the head or neck of people with epilepsy may induce a sudden disturbance in the brain
• People with Heart Problems
• Self-management strategies
• People with a pacemaker or another type of electrical or metal implant

Treatment Parameters:

• Pulse shape - usually rectangular.
• Pulse width - is measured in microseconds and is between 100 and 500us.
• Frequency - can be as low as 2 Hz or as high as 60 Hz. A frequency of 150 Hz is commonly used. The frequency can be selected and altered by the therapist.
• Intensity – can be varied from 0 to 60 milliamps (mA) on many units. The patient or therapist can control the intensity and a tingling sensation should be felt.

The wide range of variations in pulse width, frequency, and intensity gives flexibility in terms of the treatments applied to patients with chronic pain syndromes.

Vacuum electrodes or rubber electrodes are strapped or fixed with adhesive tape and covered with a conductive gel and then placed on the patient’s skin. The wires connecting the electrodes to the unit can be concealed by clothing.
Positioning of Electrodes
A number of approaches may be used. Electrodes can be placed over

• Acupuncture points, motor points, or trigger points.
• Area of greatest intensity of pain
• Appropriate dermatome or spinal segment
• Appropriate peripheral nerve

Whichever position is chosen for electrode placement, it is best if the skin below them has an intact sensory mechanism as it is the large-diameter afferent sensory stimulation produced by the TNS current acting on the skin that produces the effect on pain. Once the electrodes have been positioned, the TENS can be applied by setting the parameters.