Electrical muscle stimulation -- often called "e-stim" or "TENS" -- is a type of treatment often used in physical therapy or other rehabilitation settings. The two primary uses for this treatment are pain relief and muscle re-education. In most settings, there is a machine that provides an electrical current. Wires from the machine are connected to adhesive patches that are placed on the skin over a predetermined area. Electrical current is then sent from the machine to the patches and delivered into the muscle tissue below, causing a sensory or motor response.
For Pain Relief
Electrical stimulation can be used for pain relief. There are two theories as to why it relieves pain. The Gate Control Theory says that pain signals are sent to the brain via nerves but must pass through a "gate." The stimulation sensation from e-stim is said to pass through the gate, thus blocking the nerves that deliver pain sensations. Another theory is that the stimulation causes the brain to release the body's natural painkillers -- endorphins and enkephalins -- resulting in pain relief. Studies have shown marked increases in these chemicals after the use of low-frequency electrical stimulation.
For Muscle Re-Education
Electrical stimulation is also used for re-training muscles that are having trouble contracting. Though used for various conditions, it is commonly used for people who have had a stroke or an orthopedic surgery. Many times these patients have trouble trying to move a muscle or joint. When the electrical impulse is sent into into the muscle tissue with e-stim, under the appropriate settings, the muscle can contract without the help of the patient. Doing this while having the subject actively try to contract the muscle can sometimes get the brain to re-learn how to contract the muscle on its own.
Controversy and Research
Although numerous research studies have been conducted on the use of electrical stimulation, its clinical effectiveness is questionable. Many studies have found little or no benefit from electrical stimulation when compared to a placebo. In fact, electrical stimulation is often classified under alternative medicine due to the lack of evidence on its usefulness. Still other studies find just the opposite. For example, a 2014 study on people with moderate to severe acute pain showed that e-stim produced a clinically significant reduction in pain severity. Research continues to be performed on its effectiveness for pain relief.
Benefits and Shortcomings
Electrical stimulation has many benefits that support it in being an effective way to manage pain and re-train muscles after injury or disease. E-stim is non-addictive. The machines are often compact and user-friendly. They are cost-effective and provide many with an alternative to taking pain medications. There are few risks associated with the use of e-stim. The main shortcoming of e-stim usage is that it will not solve the underlying condition when it comes to pain. For muscle re-education, the main shortcoming is that even though it can cause a muscle to contract, function may not return if the neurological damage is severe. E-stem also will not lead to significant strength gains, despite some advertisement claims.