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(EMG) measures the electrical activity of muscles when they're at rest and when they're being used. Nerve conduction studies measure how well and how fast the nerves
can send electrical signals.
Nerves control the muscles in the body with
electrical signals called impulses. These impulses make the muscles react in
certain ways. Nerve and muscle problems cause the muscles to react in ways that aren't normal.
If you have leg pain or numbness, you may have these tests to find out which nerves are being affected and how much they are affected. These tests check how well your spinal nerves are working. They also check the nerves in your arms and legs.
EMG is done to:
A nerve conduction study is done
Be sure to tell your doctor about all the medicines you take, even over-the-counter ones. Many medicines can change the results of this test.
clothing to make it easier to do the test. You may get a hospital
gown to wear.
The electrodes are attached to your skin. So make sure your skin is clean. Don't use any sprays, oils, creams, or lotions.
You may be asked to sign a consent form that says you understand the risks of the test and agree to have it done.
Talk to your doctor if you have any concerns about the need for the
test, its risks, how it will be done, or what the results will mean. To help
you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).
An EMG is done in a
hospital, a clinic, or a doctor's office. It may be done in a room that stops any outside
electrical activity that can interfere with the test. The test may be done by an EMG
technologist or a doctor.
You will be asked to lie on
a table or bed. Or you may sit in a chair that leans back so your muscles are relaxed.
The skin over the areas being
tested is cleaned. A needle electrode is put into a muscle. The electrode is attached by
wires to a recording machine.
When the electrodes are in place, the electrical activity in that muscle
is recorded while the muscle is at rest. Then the technologist or doctor asks
you to tighten (contract) the muscle slowly and steadily. This electrical
activity is recorded.
The electrode may be moved a number of times. This is done
to record the activity in different parts of the muscle or in different
The electrical activity in the muscle is shown as wavy
and spiky lines on a video screen. It may also be heard
on a speaker. You may hear popping sounds like a machine gun when you contract the
muscle. The activity may also be recorded on video.
An EMG may
take 30 to 60 minutes. When the test is done, the electrodes are removed. The places where a needle was put in the skin are cleaned.
In this test, several
flat metal-disc electrodes are attached to your skin with tape or a paste. An electrode that puts out electric pulses is placed right over the nerve. Then a
recording electrode is placed over the muscles controlled by that nerve.
Several quick electrical pulses are given to the nerve. The time it takes
for the muscle to contract in response to the electrical pulse is recorded. The
speed of the response is called the conduction velocity.
nerves on the other side of the body may be studied. The results from both sides of the body can be compared. When the
test is done, the electrodes are removed.
studies are done before an EMG if both tests are being done. Nerve conduction
tests may take from 15 minutes to 1 hour or more. How long the tests take depends on how many nerves
and muscles are studied.
During an EMG test, you
feel a quick, sharp pain when the needle electrode is put into a muscle.
After the test, you may be sore and feel a tingling in your muscles. This may last
for up to 2 days. Call your doctor if your pain gets worse. You should also call if you have swelling, tenderness, or
pus at any of the needle sites.
If you have pain after the test:
conduction studies, you will be able to feel the electrical pulses. The tests make some people anxious. Keep in mind
that only a very low-voltage electrical current is used. And each electrical
pulse is very quick. It lasts less than a second.
An EMG is very safe. You may
get some small bruises or swelling at some of the needle sites. The needles are
sterile, though. There is very little chance of getting an infection.
There is no chance of problems with nerve conduction studies. Nothing is
put into your skin, so there is no chance of infection. The voltage of
electrical pulses is too low to cause an injury.
Your doctor may be able to tell you some of the results of your nerve studies right after the tests. A full report may take 2 to 3
The EMG recording shows no electrical activity when the
muscle is at rest. There is a smooth, wavy line on the recording with each
The nerve conduction studies show that the nerves
send electrical impulses to the muscles or along the sensory nerves at
normal speeds, or conduction velocities. Sensory nerves allow the brain to feel
pain, touch, temperature, and vibration. Not all nerves have the same normal
conduction velocities. They generally get slower as a
person gets older.
Electrical activity in a muscle at rest shows that there
may be a problem with the nerves used by the muscle. Abnormal wave lines when
a muscle contracts may mean there is a muscle or nerve problem. Examples include
a herniated disc, amyotrophic lateral sclerosis (ALS),
In nerve conduction studies, the speed of nerve impulses is slower than normal for that nerve. Slower
speeds may be caused by injury to a nerve or group of nerves.
The results from EMG and nerve conduction studies are looked at
along with other things. These include your medical history, symptoms, physical and neurological exams, and
the results of other tests. All of these things may help your doctor find the problem or
see how a disease is changing.
You may not be able to
have the test, or the results may not be helpful, if:
Other Works Consulted
Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
ByHealthwise StaffPrimary Medical ReviewerAnne C. Poinier, MD - Internal MedicineSpecialist Medical ReviewerColin Chalk, MD, CM, FRCPC - Neurology
Current as ofMarch 12, 2015
Current as of:
March 12, 2015
Anne C. Poinier, MD - Internal Medicine
& Colin Chalk, MD, CM, FRCPC - Neurology
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