Electromyography (EMG) is a diagnostic test that measures how well the muscles respond to the electrical signals emitted to specialized nerve cells called motor nerves.
A doctor may order an EMG test if a person has symptoms of a muscular or neurological condition, such as numbness or unexplained weakness in the limbs.
Doctors often conduct EMG tests in conjunction with nerve conduction velocity (NCV) tests. An NCV test is another type of electrodiagnostic test that doctors can use to identify damaged or impaired nerves.
EMG and NCV tests are safe procedures that pose little risk of serious side effects or complications. However, they may cause discomfort and bruising at the entry point of the needle.
In this article, learn more about their purpose, what to expect during the procedure, and how to prepare for it.
Motor nerve cells, or neurons, transmit electrical signals from the central nervous system to the muscles. The electrical signals from the nerves trigger muscle contractions.
Motor nerves control skeletal muscle activity, such as walking, speaking, and breathing.
Damaged or diseased muscle fibers do not function or respond to nerve impulses appropriately.
If the motor nerves are damaged or diseased, they can send abnormal electrical signals to the muscles.
A doctor may order an EMG test if a person has symptoms of a muscle or nerve condition.
Such symptoms may include:
- muscle weakness or stiffness
- muscle wasting
- twitching, cramping, or spasms
- loss of fine motor control
- difficulty speaking, chewing, or swallowing
- persistent pain in the feet, legs, arms, or hands
- numbness, tingling, or paralysis in the limbs
EMG tests also provide information that doctors can use to determine the location and extent of muscle and nerve damage.
EMG is an outpatient procedure that can take place at a hospital or an office clinic.
Neurologists and physical medicine and rehabilitation physicians perform EMG tests. Neurologists specialize in treating, diagnosing, and managing conditions affecting the nervous system.
A neurologist can administer an EMG test alone or with the help of a specially trained technician.
How to prepare
A neurologist will explain how the procedure works and what to expect during and after the test. At this point, a person can bring up any questions they have with the neurologist.
A person should notify the neurologist if they:
- take any over-the-counter or prescription medications, especially blood thinners
- have a bleeding disorder
- have a cardiac defibrillator or pacemaker
To prepare for the test, a person should:
- Bathe or take a shower the night before or the morning of the test to remove excess oil from the skin.
- Avoid applying lotions, creams, or body oils for a few days before the test.
- Dress in comfortable, loose-fitting clothes.
- Remove any jewelry, watches, eyewear, or other metal objects before the procedure.
During the procedure
The following sections describe what to expect from needle EMG and NCV tests.
Needle EMG procedure
A needle EMG test measures how well the muscles respond to electrical impulses.
A neurologist or assisting technician will insert one or more thin, sterile needles into the muscle. This may cause some minor discomfort in some people.
The needles detect the electrical activity of muscles at rest and while contracted.
The needle electrodes transmit this information to a device called an oscilloscope, which displays electrical signals as waves.
Once the test is finished, the neurologist or technician will remove the needle or needles.
This test usually examines several nerves and muscles and lasts about 1 hour, but it may take longer depending on how many nerves the neurologist wants to test.
A neurologist will most often administer an EMG test alongside an NCV test, according to the National Institutes of Health (NIH).
An NCV test measures the strength and speed of electrical impulses as they move through nerves. Doctors often use these results alongside those of an EMG test to get a full picture of what is going on with a person’s nerves.
During an NCV test, the neurologist will ask a person to sit or lie down. Once the person is ready, they will attach a recording electrode to the skin above the nerve or nerves under investigation. They will attach a second electrode about 20 millimeters away.
This electrode emits low voltage electric shocks that activate the nerve.
Some people may experience mild discomfort during this part of the test. However, the electric shocks should not cause pain, and any discomfort usually resolves once the test is over.
The recording electrode detects the electrical impulse as it passes through the nerve and transmits the response to a computer monitor.
After the procedure
After an EMG test, the neurologist or technician will clean the skin, and a person should be able to return to their normal activities.
However, they may experience some soreness and bruising for a few days afterward.
EMG tests carry minimal risk of severe complications or side effects. However, many people do experience muscle pain during or after a needle EMG.
Resting and taking over-the-counter pain relievers can help relieve muscle pain faster, but this side effect usually resolves on its own within a few days.
In very rare cases, a person may experience swelling of the soft tissues (lymphedema) or a skin infection near the puncture site after a needle EMG test.
Some people may experience more discomfort or pain during an NCV test.
In fact, in one 2014 study, researchers surveyed 200 people who received both EMG and NCV tests, and 58.5% of them said that the NCV test was more uncomfortable.
If the neurologist who ordered the EMG test is present, they may review a person’s results immediately. However, if a different healthcare professional administers the test, the person will not get to see their results until they schedule a follow-up appointment with their neurologist.
Both EMG and NCV tests can help doctors identify the underlying cause of any neuromuscular symptoms.
EMG test results
If the muscles are healthy, an EMG test should detect little electrical activity when the muscle is relaxed.
A burst of electrical activity, or a “motor unit action potential,” appears when a nerve stimulates a muscle contraction.
If an EMG test detects electrical activity in a relaxed muscle, it may be due to:
- carpal tunnel syndrome
- inflammation of the muscle tissue (myositis)
If an EMG test shows sporadic, random activity during a muscle contraction, it may indicate:
- amyotrophic lateral sclerosis
- spinal muscular atrophy
- carpal tunnel syndrome
EMG and NCV tests provide valuable information that doctors can use to diagnose muscle and nerve conditions. Once they make a diagnosis, a doctor can recommend different treatment options.
Anyone who has concerns or questions about their test result or treatment plan should speak with their doctor.
An EMG test is a minimally invasive procedure that health professionals use to diagnose and monitor muscle dysfunction. Neurologists and trained technicians can administer EMG tests.
During the procedure, a neurologist will insert thin, needle-shaped electrodes into a muscle. These electrodes record the electrical activity of relaxed and contracted muscles.
Neurologists tend to perform an EMG test after an NCV test, which measures how fast electrical impulses travel through motor nerves.
Both EMG and NCV tests provide useful information that helps doctors determine the location and extent of muscle and nerve damage.