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What is an EMG (electromyography)?
Electromyography (EMG) is a diagnostic test that evaluates the health and function of your skeletal muscles and the nerves that control them. It’s one form of electrodiagnostic testing.
Every body movement you make, from lifting your leg to nodding your head, involves complex communication between your central nervous system (your brain and spinal cord), nerves and muscles. To produce movement, your motor (movement) nerves send electrical signals to your muscles. An EMG can detect issues with your motor nerves, muscles or the communication between the two.
Neurologists often perform an EMG test alongside a nerve conduction study (NCS). An NCS measures the flow of electrical current through a nerve before it reaches a muscle. An EMG measures the response of muscles to electrical activity and how much electrical activity a muscle contraction produces.
Your healthcare provider may recommend an EMG if you have symptoms such as muscle weakness or numbness and tingling. You may have an EMG in an outpatient setting or as part of your stay in a hospital, depending on your situation.
What can an EMG diagnose?
An EMG can help diagnose several injuries or diseases that affect your motor nerves and muscles. It can help determine the presence, location and extent of these injuries and diseases. Providers may also use EMG tests to rule out conditions.
Categories of conditions an EMG can help diagnose include:
- Issues that affect your peripheral nerves, such as peripheral neuropathy and nerve compression syndromes like carpal tunnel syndrome.
- Issues that affect the nerve roots that exit your spinal column, such as pinched nerves, cervical (neck) radiculopathy or sciatica.
- Muscle disorders (myopathies), such as muscular dystrophy, polymyositis and dermatomyositis.
- Conditions that affect the motor neurons in your brain or spinal cord, such as amyotrophic lateral sclerosis (ALS) or post-polio syndrome.
- Conditions that affect the connection between your nerves and muscles, such as myasthenia gravis.
Providers use other tests in conjunction with electromyography to diagnose these conditions, such as imaging tests, blood tests and muscle biopsies.
How does an EMG test work?
To understand how an EMG test works, it helps to understand how your muscles work.
Your motor nerves (motor neurons) send electrical signals to your muscles to tell them what to do. (These signals originate in your brain, travel down your spinal cord, through your motor nerves and to your muscles.) This electrical stimulation causes electrical activity in your muscles, which causes them to contract (tighten). The muscle contraction itself also produces electrical activity.
Normally, a muscle at rest has no electrical activity. A slight contraction of the muscle results in some electrical activity, which increases as the muscle contracts more intensely.
In electromyography, a healthcare provider inserts a small needle with an electrode into one of your muscles to record its electrical activity. The provider doesn’t deliver electrical stimulation through the needle. Instead, you can think of the needle as being similar to a microphone — it’s only a recording device.
As you rest or contract your muscle, the needle electrode records the electrical activity. The needle is attached through a cable to a computer that allows the provider to see what your muscle is doing both at rest and with movement. It appears as waves on a screen. They may also use an audio amplifier so they can hear the pulses of electrical activity.
The provider then analyzes these readings to look for signs of issues. For example, if your muscle is damaged, it may have abnormal electrical activity when it’s resting. When it contracts, its electrical activity may make abnormal wave patterns.
How do I prepare for an EMG test?
Before you have an EMG, you should:
- Bathe or shower and wear comfortable, loose-fitting clothing.
- Avoid putting cream, lotion or perfume on your skin. Creams and lotions can affect the test’s accuracy.
- Tell the healthcare provider who’s performing the EMG if you’re taking a blood thinner medication (anticoagulant) such as warfarin. Blood thinners may increase your risk of bleeding after an EMG. But don’t stop taking your medication without talking to the provider who prescribes the medication.
- Tell the provider if you have a pacemaker or any other electrical medical device.
In some cases, your provider may instruct you to not smoke cigarettes or drink caffeinated beverages, such as coffee or tea, two to three hours before testing. These substances may interfere with the test.
What happens during an EMG test?
Neurologists usually perform an EMG test right after a nerve conduction study. During the nerve conduction study, a provider will put electrodes (stickers) on the surface of your skin. They’ll then deliver a small electrical impulse that will feel like a shock to nerves and record the response. In most cases, they’ll test several different nerves.
The process can vary for an EMG, depending on the reason for the test and which muscles and nerves the provider is assessing. But in general, you can expect the following during an EMG test:
- You’ll sit or lie down for the test.
- A provider will locate the muscle(s) they want to test.
- They’ll then insert a small needle with an electrode through your skin and into your muscle. These needles will stay in your muscles, and the duration of the examination for each muscle generally takes one to two minutes. You may feel slight discomfort or pain when they insert the needles.
- The provider will ask you to relax and then use your muscles in certain ways, such as lifting or flexing one of your limbs, at certain times. A machine will measure and display the electrical activity of your working muscle. There will also be an audio (sound) component to the machine.
- After the provider has recorded enough data from your muscle, they’ll remove the needle. They’ll repeat the same process in the next muscle until the test is concluded.
How painful is an EMG test?
You may feel some pain or discomfort when your provider inserts the needle into your skin and muscles. But most people can complete the test without issues.
After the test, the muscles they tested may feel tender for a few days.
How long does an EMG test take?
The test usually takes 60 to 90 minutes. It depends on how many muscles your provider needs to test.
What should I expect after an EMG test?
You may have sore or tender muscles for a few days after the test. The muscle soreness isn’t usually severe and should get better in less than a week. You may also see some bruising where the needles entered your skin.
What are the risks of an EMG?
EMG is generally safe. Complications are rare. Some people (especially people who take blood thinner medications) may bleed after the test.
Results and Follow-Up
What do the results of an EMG test mean?
Although EMG tests can be very helpful, they alone don’t usually provide a diagnosis. Your healthcare team providers will assess the results in conjunction with other medical tests to determine a diagnosis.
When should I know the results of an electromyography (EMG) test?
You can expect to receive the results of the test typically within 24 to 48 hours after the testing is completed.
When should I call my doctor about my EMG?
Call your healthcare provider if you have:
- Bleeding that doesn’t stop.
- Severe pain or tenderness where the needles entered your skin.
- Redness, warmth, swelling or a fever. These may be signs of an infection.
Frequently Asked Questions
Will an EMG show a pinched nerve?
An EMG can help diagnose a pinched nerve and issues related to it, but it can’t “show” a pinched nerve. Imaging tests like X-rays, CT scans and MRI scans help healthcare providers see a pinched nerve and what’s causing it (such as a herniated disk).
A note from Cleveland Clinic
If you have signs of muscle disease, nerve damage or injury, an electromyography (EMG) test will help your provider learn more about what’s going on. It also helps your provider plan treatment. If you have any questions about the test, don’t hesitate to ask. Your provider is available to help and support you.
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