What is EMG and Nerve Conduction Study?

Medically Reviewed by Christopher Melinosky, MD on May 12, 2023
4 min read

When your muscles are sore or weak and you don’t know why, there are a couple of tests that can help give you answers.

One is electromyography (EMG). The other is a nerve conduction study (NCS). They are often done at the same time.

Your doctor can use the results of these tests to figure out whether you have a muscular problem or a nerve problem.

Your muscles move when nerve signals from the brain tell them to get to work. Electromyography measures how well your muscles respond to those signals.

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.

NCS measures how fast and how strong the electrical activity is in a nerve. 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 lifting something heavy, for example.

For many people, though, 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 other body part, one or both of these tests 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 tests can help doctors diagnose what’s wrong with you. They can also help rule out conditions that you don’t have. EMG and NCS are helpful in diagnosing:

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

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

  • Bathe or shower, but don’t put on any lotions or moisturizers
  • Avoid caffeine and sugary beverages for at least 2 or 3 hours before a test
  • Don’t smoke before a test

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, you should tell your doctor before they schedule NCS or EMG.

EMG and NCS are done in a hospital or office setting. They can be “outpatient procedures,” meaning you don’t stay overnight and you expect to 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 are doctors who specialize in the brain and nervous system. A hospital technician may be the person who actually does the NCS or EMG.

Nerve conduction study: 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 able to repair an injured nerve.

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

Electromyography: This is more involved than NCS. It may also be a little more uncomfortable.

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 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:

Neither NCS nor EMG should lead to any complications. You may have some soreness for a day or two where the needles were inserted during EMG. If you notice any swelling or signs of infection around the needle marks, tell your doctor.

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

If the studies suggest that 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, surgical procedures, or lifestyle changes.

Neither NCS or EMG will solve your muscle or nerve problems, but they will give doctors key information about how to help you start feeling better soon.