What is EMG?

EMG stands for ElectroMyoGraphy. An EMG test measures the electrical activity of muscles when they are at rest and when they are being used.

What are they used for?

EMG and nerve conduction studies are used to help diagnose a variety of muscle and nerve disorders. An EMG test helps find out if muscles are responding the right way to nerve signals. Nerve conduction studies help diagnose nerve damage or disease. When EMG tests and nerve conduction studies are done together, it helps providers tell if your symptoms are caused by a muscle disorder or a nerve problem.

These tests are done separately, but they are usually done at the same time.

Procedure for a nerve conduction study:

  • You will sit or lie down on a table or bed.
  • Your provider will attach one or more electrodes to a certain nerve or nerves using tape or a paste. The electrodes, called stimulating electrodes, deliver a mild electrical pulse.
  • Your provider will attach different types of electrodes to the muscle or muscles controlled by those nerves. These electrodes will record the responses to the electrical stimulation from the nerve.
  • Your provider will send a small pulse of electricity through the stimulating electrodes to stimulate the nerve to send a signal to the muscle.
  • This may cause a mild tingling feeling.
  • Your provider will record the time it takes for
    your muscle to respond to the nerve signal.

The speed of the response is called the conduction velocity.

Procedure for an EMG test:

  • You will sit or lie down on a table or bed.
  • Your provider will clean the skin over the muscle being tested.
  • Your provider will place a needle electrode into the muscle. A needle electrode is a special wire that a mild electric current flows through. You may have slight pain or discomfort when the electrode is inserted.
  • The machine will record the muscle activity while your muscle is at rest.
  • Then you will be asked to tighten (contract) the muscle slowly and steadily. The machine will record this activity.
  • The electrode may be moved to record activity in different muscles.
  • The electrical activity is recorded and shown on a video screen. The activity is displayed as wavy and spiky lines. The activity may also be recorded and sent to an audio speaker. You may hear popping sounds when you contract your muscle.

If you are having both tests, the nerve conduction study will be done first.

Why do I need an EMG test and a nerve conduction study?

You may need these tests if you have symptoms of a muscle or nerve disorder. These symptoms include:

Nerve compression, neck pain, mid back pain, low back pain, paresthesias (numbness, tingling, burning) and/or weakness of the arms and legs ,Muscle weakness, Pain, Tingling or numbness in arms, legs, hands, feet, and/or face, Muscle cramps, spasms, and/or twitching, Paralysis of any muscles

Some of the common disorders that can be diagnosed by nerve conduction studies are:

  • Carpal tunnel syndrome, a condition that affects nerves in the hand and arm. It’s usually not serious, but can be painful.
  • Herniated disc, a condition that happens when a part of your spine, called a disc, is damaged. This puts pressure on the spine, causing pain and numbness
  • Guillain-Barre syndrome, an autoimmune disorder that affects the nerves. It can lead to numbness, tingling, and paralysis. Most people recover from the disorder after treatment
  • Myasthenia gravis, a rare disorder that causes muscle fatigue and weakness.
  • Muscular dystrophy, an inherited disease that seriously affects muscle structure and function.
  • Charcot-Marie-Tooth disease, an inherited disorder that causes nerve damage, mostly in the arms and legs.
  • Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease. This is a progressive, ultimately fatal, disorder that attacks nerve cells in your brain and spinal cord. It affects all the muscles you use to move, speak, eat, and breathe.