Brain & Nervous System Health Center
Electromyogram (EMG) and Nerve Conduction Studies
An electromyogram (EMG) measures the electrical activity of muscles at rest and during contraction. 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 specific ways. Nerve and muscle problems cause the muscles to react in abnormal ways.
If you have leg pain or numbness, you may have these tests to find out how much your nerves are being affected. These tests check how well your spinal cord, nerve roots, and nerves and muscles that control your legs are working.
Why It Is Done
An EMG is done to:
- Find diseases that damage muscle tissue, nerves, or the junctions between nerve and muscle. These problems may include a herniated disc, amyotrophic lateral sclerosis (ALS), or myasthenia gravis (MG).
- Find the cause of weakness, paralysis, or muscle twitching. Problems in a muscle, the nerves supplying a muscle, the spinal cord, or the area of the brain that controls a muscle can cause these symptoms. The EMG does not show brain or spinal cord diseases.
A nerve conduction study is done to:
- Find damage to the peripheral nervous system, which includes all the nerves that lead away from the brain and spinal cord and the smaller nerves that branch out from those nerves. This test is often used to help find nerve problems such as carpal tunnel syndrome or Guillain-Barré syndrome.
How To Prepare
Tell your doctor if you:
- Are taking any medicines. Certain medicines that affect the nervous system can change electromyogram (EMG) results. You may need to stop taking these medicines 3 to 6 days before the test.
- Have had bleeding problems or take blood thinners, such as warfarin or heparin. If you take blood thinners, your doctor will tell you when to stop taking them before the test.
- Have a pacemaker.
Do not smoke for 3 hours before the test.
Do not eat or drink foods that contain caffeine (such as coffee, tea, cola, and chocolate) for 2 to 3 hours before the test.
Wear loose-fitting clothing so your muscles and nerves can be tested. You may be given a hospital gown to wear.
For an EMG, you may be asked to sign a consent form. Talk to your doctor about any concerns you have regarding 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
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How It Is Done
An EMG is done in a hospital, clinic, or doctor's office. It may be done in a room that stops any outside electrical interference. The test may be done by an EMG technologist or a doctor.
WebMD Medical Reference from Healthwise
