The nerves in the body control how the muscles work by sending electrical impulses. An electromyogram (EMG) is a test that measures the electrical activity of muscles both at rest and during contraction. Nerve conduction velocity studies (NCVs) measure how fast the nerves can send electrical signals.
Neck or back pain, weakness, muscle twitching, or pain and numbness in the extremities could all indicate a problem or disease which may be diagnosed by performing EMGs and NCVs. Some conditions that are diagnosed using these tests include carpal tunnel, neuropathies, and herniated discs, as well as more serious conditions such as amyotrophic lateral sclerosis (ALS), Guillain-Barre syndrome and other neurological diseases.
There is no special preparation for these tests, except having clean skin with no lotions or oils. Also, keeping your hands and feet warm until the test will help in obtaining accurate results.
An EMG is performed by inserting small needles into the muscles of the arm, leg or back to examine the electrical activity caused by a muscle contraction.
When the electrodes are in place, the electrical activity in that muscle is recorded while the muscle is at rest. Then the doctor asks you to contract the muscle slowly and steadily. This electrical activity is recorded. The electrical activity in the muscle shows as wavy lines on a monitor and also heard as popping noises when the muscle is contracted. The electrode may be moved a number of times to record the activity in different areas of the muscle or in different muscles.
Nerve Conduction Studies
In this test, several electrodes are attached to your skin with tape or a paste. A shock-emitting electrode is placed directly over the nerve, and a recording electrode is placed over the muscles controlled by that nerve. Several quick electrical pulses are given to the nerve, and the time it takes for the muscle to contract in response to the electrical pulse is recorded. The speed of the response is called the conduction velocity. The same nerves on the other side of the body may be studied for comparison.
Nerve conduction studies are done before an EMG if both tests are being done. Nerve conduction/EMG tests may take from 15 minutes to 1 hour or more, depending on how many nerves and muscles are studies.