Electromyography (EMG) is a diagnostic test measuring how well the muscles respond to the electrical signals emitted to specialized nerve cells called motor nerves.
If a person has symptoms of a muscular or neurological condition such as numbness or unexplained weakness in the limbs, a doctor may order an EMG test.
Doctors frequently conduct EMG tests in conjunction with NCV tests. An NCV test is another type of electrodiagnostic test which can be used by doctors to detect damaged or impaired nerves.
Monitoring EMG and NCV are healthy procedures with little risk of serious side effects or complications. These can however cause discomfort and bruise at the needle’s entry point.
Learn more about its purpose in this article, what to expect during the procedure and how to prepare for it.
The motor nerve cells, or neurons, transmit electrical signals to the muscles from the central nervous system. The electrical nerve signals induce contractions in the muscles.
Motor nerves regulate the movement of the skeletal muscles, such as walking, talking and breathing.
Weakened or diseased muscle fibers do not function or respond appropriately to nerve impulses.
If the motor nerves are weakened or ill they will give the muscles irregular electrical signals.
If a person has symptoms of a muscle or nerve disorder, a doctor can order an EMG test.
Such symptoms might 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 give information that can be used by physicians to determine the location and severity of muscle and nerve damage.
EMG is an ambulatory treatment that can be performed in a hospital or in an outpatient unit.
Neurologists and doctors in physical therapy and rehabilitation do EMG research. Neurologists specialize in the prevention, diagnosis, and management of nervous system related disorders.
A neurologist can perform an EMG test on his own, or with the aid of a specially trained technician.
How to prepare
A neurologist may explain the operation of the procedure and what to expect during and after the test. At this point, a person can put up with the neurologist any questions they have.
If they do, a person should tell the neurologist:
- 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 electrical impulses are responding to the muscles.
A neurologist or technician who assists will insert one or more thin, sterile needles into the muscle. In some people this can cause some minor discomfort.
The needles detect at rest and while contracting the electrical activity of the muscles.
The needle electrodes pass this information on to an oscilloscope device which displays electrical signals as waves.
The neurologist or technician will remove the needle or needles once the test is complete.
Usually this test 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.
According to the National Institutes of Health (NIH), a neurologist will most likely perform an EMG examination alongside an NCV test.
An NCV test measures the force and velocity of electrical impulses as they move through the nerves. Doctors often use these results alongside an EMG test to get a complete picture of what happens to a person’s nerves.
The neurologist will ask one person to sit or lie down during a NCV test. Once the person is ready, the person under investigation will attach a recording electrode to the skin above the nerve or nerves. They’ll attach about 20 millimeters away from a second electrode.
This electrode emits electrical shocks at low voltage which activate the nerve.
During this part of the test some people may experience mild discomfort. The electric shocks are not supposed to cause pain, however, and any discomfort usually resolves once the test is over.
The electrical impulse is recorded by the recording electrode as it passes through the nerve and transmits the response to a computer monitor.
After the procedure
The neurologist or technician will cleanse the skin after an EMG test, and a person should be able to return to their normal activities.
Though, a few days later they can feel some soreness and bruise.
Tests with EMG carry minimal risk of serious complications or side effects. However, during or after an EMG needle, many people do experience muscle pain.
Resting and taking pain relievers over- the-counter can help relieve muscle pain quicker, but this side effect usually resolves itself within a few days.
In very rare cases, after a needle EMG examination, a person may experience soft tissue swelling (lymphedema), or a skin infection near the puncture site.
During a NCV check, some people may experience more discomfort or pain.
In addition, researchers surveyed 200 people who received both EMG and NCV tests in one 2014 sample, and 58.5 percent said the NCV test was more painful.
If there is a neurologist who ordered the EMG test, they could immediately check a person’s results. Nevertheless, if the examination is performed by another health care professional, the individual will not see their results until a follow-up appointment with their neurologist is arranged for them.
Both EMG and NCV tests will help doctors recognise any neuromuscular symptoms as the underlying cause.
EMG test results
If the muscles are stable, then when the muscle is relaxed, an EMG check will detect Little electrical activity.
When a nerve activates a muscle contraction, a burst of electrical activity, or “potential motor unit motion,” occurs.
Where an EMG test detects electrical activity in a relaxed muscle, this may be because of:
- 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 which can be used by doctors to diagnose muscle and nerve conditions. Once a diagnosis is made a doctor can recommend different treatment options.
Anyone with concerns or questions regarding their test result or treatment plan should talk to their doctor.
The EMG check is a minimally invasive operation used by health professionals to treat and control dysfunctional muscles. Neurologists and qualified technicians are allowed to administer EMG monitoring.
A neurologist must inject small, needle-shaped electrodes into one muscle during the procedure. Such electrodes monitor the electrical activity of muscles relaxing and contracting.
After a NCV test, neurologists tend to perform the EMG test which measures how quickly electrical impulses pass through motor nerves.
Both EMG and NCV tests provide useful information which helps doctors identify the location and extent of muscle and nerve damage.