Originally published by Harvard Health.
What is the test?
Electromyography (EMG) tests analyze nerve and muscle electrical activity. Some types of electrical activity are normal, whereas some patterns of electrical activity suggest a disease of nerves or muscles. Nerve conduction studies are tests that are often used in combination with the EMG evaluation. For nerve conduction studies, the muscles and nerves are stimulated with small bursts of electricity to see whether the nerves and muscles respond in a normal way.
How do I prepare for the test?
No preparation is necessary.
What happens when the test is performed?
For the EMG, thin needles are inserted one by one into the muscles being tested. These needles are not hollow, and they are thinner than the type of needle used to draw blood. Each needle is attached to a wire that gives signals to a machine. The needle acts like an antenna to detect electrical patterns inside the muscle and the nerves that are attached to that muscle. Most patients find this test mildly uncomfortable.
If you have nerve conduction studies done, small pads are taped to the skin on your hands or feet. These pads can both deliver mild electric shocks and detect electric signals coming through the skin. The shocks that are used are too small to be harmful. They feel similar to the kind of shock you might feel if you rubbed your feet on the carpet and then touched a doorknob. You might feel one of your muscles twitch when the electricity is delivered.
Testing times vary, depending on how many muscles are being tested. EMG testing takes 20 to 30 minutes. If nerve conduction studies are also done, testing may require as long as one hour.
What risks are there from the test?
There are no risks. The needles used in the EMG are too small to put you at significant risk for bleeding or infection. The shocks do not shock your whole body and are too mild to cause any damage.
Must I do anything special after the test is over?
How long is it before the result of the test is known?
A neurologist interprets the electrical signals measured in your muscles and sends a report to your doctor within a few days.