Electromyography (EMG) and Nerve Conduction Study

Medically Reviewed by Zilpah Sheikh, MD on March 14, 2024
7 min read

Your muscles move when nerve signals from the brain tell them to get to work. Electromyography (EMG), a diagnostic test, measures how well your muscles respond to those signals.

Movement is a complex interaction between your central nervous and muscular systems. Your doctor can use the results of an EMG to determine whether you have a muscular problem, a nerve problem, or both.

Motor neurons are the nerve cells that send signals to your muscles to move. During the test, a needle probe is inserted into your muscle to measure its electrical activity. The EMG turns the electrical activity into sounds, graphs, or numbers for your doctor to interpret.

If the test picks up a problem, you may be diagnosed with what is called a neuromuscular disorder.

Nerve signals are electrical impulses that travel quickly throughout your nervous system. Sometimes, problems with the electrical activity in your nerves can cause pain, tingling, or weakness in your muscles.

A nerve conduction study (NCS) tests the health of your peripheral nerves, the nerves located outside your central nervous system (the brain and spinal cord). An NCS measures how fast and how strong the electrical activity is in your motor (muscle) and sensory nerves. The test can tell whether a nerve has been damaged.

It’s natural to have soreness or numbness in a muscle once in a while. You might strain a wrist muscle by lifting something heavy, for example.

However, for many people, a sore wrist is caused by an injured nerve, not an injured muscle. When it’s not clear why you’re having problems with your wrist, back, legs, or any other body part, one or both of these tests (EMG and NCS) may be helpful.

The tests may be given to people who have the following symptoms that don’t go away:

  • Pain or cramping
  • Tingling or numbness
  • Muscle weakness

Both EMG and NCS can help doctors diagnose what’s wrong with you. They can also help rule out conditions that you don’t have. EMG and NCS can help diagnose:

NCS can also help your doctor see how well you’re recovering from a nerve injury.

An EMG is generally safe to undergo and there are few complications.

Very rarely, there may be:

  • An infection at the insertion site, especially if your skin is swollen there
  • Bleeding, typically if you have a bleeding disorder or are on blood thinners or certain other medicines, including some herbal supplements
  • Nerve injury in certain "high-risk" muscle areas, such as your diaphragm (the muscle you use to breathe), rib cage, rotator cuff, back and spine.

Is having an EMG painful?

When the EMG needle pricks your skin, it may feel uncomfortable. Most people expect the test to be painful but later report that the pain was much less intense than they had feared.

After the test, you may have some bruising or muscle soreness, but both should go away in about a week.

You don’t need to do anything special before either test. Doctors do recommend that on the morning of EMG monitoring, you:

  • Bathe or shower, but don’t put on any lotions or moisturizers
  • Don’t smoke 

You should also talk with your doctor about taking medications before a test. There may be certain medicines you should avoid taking until after the test.

If you have a pacemaker or implanted cardiac defibrillator (ICD), you should tell your doctor before they schedule an EMG, as it may affect how they work.

What to wear. Loose-fitting clothing that you can easily remove or that won't restrict your movement. Avoid wearing any shaping underwear, pantyhose, or long underwear.

Food and drink. You can eat as usual, but your doctor may ask that you avoid caffeine and sugary beverages for at least 2 or 3 hours before a test.

Medication. Tell your doctor what prescription, over-the-counter, or herbal medicines you take.

EMG and NCS are done in a hospital or office setting. They can be "outpatient procedures," meaning you don’t have to stay overnight and can go home the same day, or they can be done during a hospital stay.

Several types of doctors may oversee the procedures. That includes neurologists, who specialize in the brain and nervous system. A hospital technician may be the person who actually does the NCS or EMG test.

Nerve conduction study. An NCS detects damage to nerves the way an EMG tests muscle function. During the test, the technician puts electrode patches on your skin over the nerve that may be causing your symptoms. A stimulating electrode sends a mild electrical impulse to the nerve. The other electrodes record the nerve’s response.

If the signal travels at a slower rate than it should in a healthy nerve, it means the nerve is probably damaged. More tests may be needed to learn whether the nerve can become healthy again.

Sometimes, nerves injured in an accident or surgery just need time to improve. In other cases, surgery may be needed to repair an injured nerve.

An NCS is usually done before an EMG if both procedures are done in the same session.

Electromyography. This is more complex than NCS.

An EMG uses an electrode on the skin, too. However, the test uses a very thin needle that penetrates the skin and goes into your muscles.

You will be asked to relax and to contract (or flex) your muscles. You’ll be given instructions on how and when to contract the muscle being studied.

If the EMG shows that your muscles responded well to nerve signals, your doctor may look for other causes of your muscle soreness or weakness.

Some common causes are:

The neurologist supervising either or both procedures will review the results and write a summary for your doctor.

If the studies suggest you have a neuromuscular disorder or a damaged nerve, you will probably be referred to a specialist.

They may order further tests to learn more about your condition. Then a treatment plan will be drawn up. It may include medications, operations, or lifestyle changes.

Neither NCS nor EMG will solve your muscle or nerve problems, but they will give doctors key information about how to help you start feeling better soon.

Getting the results of your EMG should take 1 or 2 days. Your doctor usually won't rely solely on the results of your EMG to make a diagnosis but will instead consider it along with other tests.

Normal EMG results

Your muscles display little activity at rest. When the EMG needles are inserted, your muscles may show some electrical activity that should fade quickly. As you move and contract your muscles, an electrical pattern becomes evident. Your doctor will be able to detect normal electrical activity.

Abnormal EMG results

If your EMG results are abnormal, your doctor should be able to arrive at a diagnosis by looking at how your muscles react at rest or with activity. For example, if your EMG results are abnormal and your NCS results are normal, it may indicate a muscle condition such as myopathy, a group of disorders that cause muscle weakness. In diseases that affect your motor neurons, your EMG may show abnormal muscle activity at rest.

Abnormal EMG results can indicate numerous conditions such as carpal tunnel syndrome, sciatica, peripheral neuropathy, myasthenia gravis, amyotrophic lateral sclerosis (ALS), and various forms of muscular dystrophy.

Post-EMG complications

Call your doctor if you have any of these symptoms:

  • Continued bleeding
  • Tenderness or pain at any puncture site
  • Muscle warmth, redness, and swelling, or fever

Your muscles move because of a complex connection between them and your nervous system. The EMG and NCS tests help determine if one or both of these systems are not working well. Both these tests are usually outpatient procedures and done together, and they typically have minimal or no side effects.

What does an EMG test diagnose?

An EMG examines how well your muscles and the nervous system's motor neurons are working together.

What does a positive EMG mean?

A positive EMG indicates that you do have a condition affecting your muscles or the nerves that control them. Your doctor will follow up to make a definitive diagnosis.

Is a nerve conduction study painful?

A nerve conduction study uses mild electrical stimulation to test your nerve function. It may tingle intensely or mildly, but any discomfort should go away after your test is over.

What does a nerve conduction study diagnose?

An NCS diagnoses peripheral nerve conditions that may affect the nerves beyond your central nervous system (the spinal cord and brain).

How long does a nerve conduction study take?

It may take about 15 minutes to an hour, sometimes longer, depending on how many nerves are examined.

Are nerve conduction studies worth it?

Nerve conduction studies are just one of the tools your doctor will use to diagnose what type of nerve damage or nerve injury you have.