What Are EMG and NCS?

Electromyography (EMG) and nerve conduction studies (NCS) are special tests used to detect neuromuscular disorders. An EMG measures the electrical activity of muscles, and NCS measure the speed and intensity of electrical signals that travel through nerves and the time it takes muscles to respond to these signals. Nerve conduction studies also are referred to as nerve conduction velocity tests (NCV).

Why EMG and NCS Are Important

These tests function as important diagnostic tools and provide vital information about the health of your nerves and muscles. They can detect the cause of such problems as muscle weakness, numbness, spasms, paralysis or pain. They also determine if the problem involves the nerves, muscles, spinal cord or brain.

How EMG and NCS Function

Both nerve and muscle cells produce minute amounts of electricity. Nerves send electrical impulses to muscles, instructing them to contract or relax. If nerves or muscles are affected by injury, disease or another condition, their electrical activity changes.

How EMG and NCS Equipment Detects Changes

Electrodes record the electrical activity of muscles or nerves, and then the data is displayed, analyzed, stored and printed by a computer. The monitor displays the electrical activity in wave patterns, and speakers audibly broadcast the activity.

What EMG and NCS Diagnose

These tests are used to detect the following:

• Pinched nerves and inflamed muscles due to injury, a ruptured disk, disease or other conditions

• Carpal tunnel syndrome, characterized by pressure on a major nerve that causes pain in the wrist or hand

• Primary muscle disorders such as muscular dystrophy (a disease that causes certain muscles to atrophy, or waste away)

• Neuromuscular disorders such as myasthenia gravis (a dysfunction in nerve impulses that leads to chronic muscle weakness)

• Nerve disorders such as amyotrophic lateral sclerosis (commonly known as Lou Gehrig’s disease)

The EMG Procedure

Some procedures may vary, but most follow these guidelines:

• While seated or lying down, certain areas of your skin may be cleaned.

• One or more needle electrodes are gently inserted into the muscle. You may experience some discomfort such as a dull ache or pressure as the electrode is inserted. The other electrodes are attached to your skin.

• The muscle is tested while at rest. Typically, there is no electrical activity within a resting muscle, and your healthcare provider may reposition electrodes to obtain readings from different sections of muscle.

• The muscle is tested when you are asked to flex. This records electrical activity, which is normal within a contracted muscle. Again, the electrodes may be moved.

• The choice of which other, if any, muscles will be tested will depend on your symptoms.

• The duration of the test ranges from about 30 minutes to more than an hour.

After Your EMG

Recovery and return to your activities of daily living may involve the following:

You may feel soreness or tenderness in the tested muscles for a few hours afterward.

If you do feel discomfort, apply ice or a cold pack, but do not apply ice directly to the skin. Instead, wrap the ice in a cloth.

Be sure to ask your healthcare provider about taking a pain reliever.

You may return home or to your hospital room. Contact your healthcare provider for the test results. They usually are available within 24 hours.