Electromyography (EMG) is that biofeedback device that tests the electrical activity of the muscles. It is often performed in conjunction with the nerve conduction study. The electrical current used during this test is very low and involves the action of the muscles and nerves.

In certain cases, the electrical activity of the muscles or nerves is abnormal. Finding and describing the electrical properties in the muscle or nerve can be a great source of help to your doctor to diagnose your condition.

EMG is known to help with the diagnosis of nerve compression or injury (e.g. carpal tunnel syndrome), nerve root injury (e.g. sciatica), and with other problems related to the muscles or nerves. It also helps with amyotrophic lateral sclerosis, myasthenia gravis, and muscular dystrophy.

EMG preparation:

This test requires no specific preparation.

How it is performed:

A small needle or pin is inserted into the skin or muscle to measure electrical activity. These needles or pins are far different from the needles used for injections. They are small and solid, and because no medication is called for, they do not cause any discomfort. This electrical activity is displayed on an oscilloscope, and can be heard on a speaker.

After placing the electrodes, you will be asked to contract the muscle by bending your arm. The presence, size, and shape of the wave form-or the action potential-is seen on the oscilloscope and provides information about the muscle’s ability to respond to a stimulus from a nerve. Along with an EMG, a nerve conduction velocity test is also performed. Along with nerve conduction studies, small electrodes are usually taped on to the skin or wound around the fingers. They give rise to a mild and brief tingling, which you may find unpleasant.

How you will feel during the test:

You may feel a certain degree of discomfort when the test is conducted.

Why the test is performed:

If you show symptoms of weakness and, on examination, impaired muscle strength becomes apparent, an EMG is conducted. This test usually takes between 30 and 60 minutes.

After the procedure:

If a doctor performs this test in his office, he will send you home once it is over and without restricting your activities in any way. You could suffer from minor aches and pains. Later, the muscle will feel tender or sore for a few days.

Normal values:

At rest, muscle tissue is usually electrically silent. Once you have gone through the trauma of the needle being inserted into your muscle, there will be no need for action on the oscilloscope.

With the muscle voluntarily contracted, action potentials will begin to appear. Once it is contracted to a greater extent, more and more muscle fibres produce action potentials until a disorderly group of action potentials with differing rates and amplitudes appear with full contraction.

What abnormal results mean:

Abnormal results include the presence of the following disorders or conditions: Polymyositis; Denervation; Carpal tunnel syndrome; Amyotrophic lateral sclerosis (ALS); Myopathy; Myasthenia gravis; Alcoholic neuropathy, among others.

EMG is a powerful tool in the world of science and medicine and its potential should be fully explored.