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What is a TENS Unit?


A TENS unit is a safe, easy-to-use, and drug-free method of pain relief used by hospitals and physiotherapists for over 50 years. TENS is an abbreviation for Transcutaneous Electrical Nerve Stimulation. The TENS unit is a small battery-operated device that produces pain relieving electrical impulses. Four self-adhesive electrodes are applied to the skin and attached to the TENS unit with lead wires. Tiny pulses are then passed from the TENS unit via the lead wires and electrodes to the nerves underneath the skin's surface. The electrodes are normally positioned around the area of pain. TENS units are medical devices regulated by the Food and Drug Administration (FDA). While many TENS units require a prescription, more and more FDA approved, over-the-counter (OTC) TENS units are becoming available.


TENS units work through 2 different mechanisms: 

First, electrical stimulation of the nerves can block a pain signal as they travel from the site of injury to the spine and upwards to the brain.  If these signals arrive at the brain we perceive pain - if they are blocked en-route to the brain we do not perceive pain - this is known as “Gate Control Theory.”  When using TENS we “close the gate” using one of the modes (Modulation, Burst, Continuous).  TENS 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. 

Secondly, the body has its own built in mechanism for suppressing pain. It does this by releasing natural chemicals called endorphins in the brain and spinal cord and these chemicals act as very powerful analgesics.  The Continuous Modulation mode produces pulse, which should be strong enough to produce a “twitch” in the muscles underneath the electrodes.  This muscle “twitch” helps to perform two benefits.  First, the “twitch” releases endorphins and also helps the pain “switches” in the brain to be activated through muscular and reflex activity.  Secondly, the “twitch” helps reduce post-operative edema if used for pain relief after surgery. 


EMS (Electrical Muscle Stimulation) is a proven way of treating muscular injuries. EMS is widely used in hospitals and sports clinics for the treatment of muscular injuries and for the re-education of paralyzed muscles, and to prevent atrophy in affected muscles. Powered muscle stimulators should only be used under medical supervision for adjunctive therapy for the treatment of medical diseases and conditions. 


EMS works by sending electronic pulses to the muscle needing treatment; this causes the muscle to exercise passively. It is effective in treating:

Relaxation of muscle spasms
Prevention or retardation of disuse atrophy
Increasing local blood circulation
Muscle re-education
Immediate post-surgical stimulation of calf muscles to prevent venous thrombosis
Maintaining or increasing range of motion. 


- Do not use this device for undiagnosed pain syndromes until consulting a physician. 
- Patients with an implanted electronic device, such as a cardiac pacemaker, implanted defibrillator, or any other metallic or electronic device should not undergo TENS treatment without first consulting a doctor. 
- Patients with heart disease, epilepsy, cancer, or any other health condition should not undergo TENS treatment without first consulting a physician. 
- Stimulation delivered by this device may be sufficient to cause electrocution.  
- Electrical current of this magnitude must not flow through the thorax or across the chest because it may cause a cardiac arrhythmia. 
- Do not place electrodes on the front of the throat as spasm of the Laryngeal and Pharyngeal muscle may occur.  
- Stimulation over the carotid sinus (neck region) may close the airways, make breathing difficult, and may have adverse effects on the heart rhythm or blood pressure. 
- Do not place the electrodes on your head or at any sites that may cause the electrical current to flow trans cerebrally (through the head.) 
- A TENS device should not be used while driving, operating machinery, close to water, or during any activity in which involuntary muscle contractions may put the user at undue risk of injury. 
- Isolated cases of skin irritation may occur at the site of electrode placement following long term application. If this occurs, discontinue use and consult your physician. 
- If TENS therapy becomes ineffective or unpleasant, stimulation should be discontinued until its use is re-evaluated by a physician. 
- Keep this device out of the reach of children unless prescribed. 
- The device has no AP/APG protection.


- The long-term effects of chronic electrical stimulation are unknown. 
- Stimulation should not be applied over the carotid sinus nerves, particularly in patients with a known sensitivity to the carotid sinus reflex.
- Stimulation should not be applied over the neck or mouth. Severe spasm of the laryngeal and pharyngeal muscles may occur and the contractions may be strong enough to close the airway or cause difficulty in breathing. 
- Stimulation should not be applied transthoracically in that the introduction of electrical current into the heart may cause cardiac arrhythmias. 
- Stimulation should not be applied transcerebrally. 
- Stimulation should not be applied over swollen infected or inflamed areas or skin eruptions, e.g., phlebitis, thrombophlebitis, varicose veins, etc. 
- Stimulation should not be applied over, or in proximity to, cancerous lesions. 


Electrical stimulators should not be used on patients with cardiac demand pacemakers. 


Although it is rare, skin irritation and burns beneath the electrodes have been reported with the use of electrical stimulators. If irritation occurs, discontinue use and consult your physician.