Electromyography (EMG) is a test that is used to record the electrical activity of muscles. When muscles are active, they produce an electrical current. This current is usually proportional to the level of the muscle activity.

EMG measures muscle response or electrical activity in response to a nerve's stimulation of the muscle. The test is used to help detect neuromuscular abnormalities.

EMGs can be used to detect abnormal electrical activity of muscle that can occur in many diseases and conditions, including muscular dystrophy, inflammation of muscles, pinched nerves, peripheral nerve damage (damage to nerves in the arms and legs), and others.

During the test, one or more small needles (also called electrodes) are inserted through the skin into the muscle. The electrical activity picked up by the electrodes is then displayed on an oscilloscope (a monitor that displays electrical activity in the form of waves). An audio-amplifier is used so the activity can be heard.

EMG measures the electrical activity of muscle during rest, slight contraction, and forceful contraction. Muscle tissue does not normally produce electrical signals during rest. When an electrode is inserted, a brief period of activity can be seen on the oscilloscope, but after that, no signal should be present.

After all of the electrodes have been inserted, patient may be asked to contract the muscle. The action potential (size and shape of the wave) that this creates on the oscilloscope provides information about the ability of the muscle to respond when the nerves are stimulated. As the muscle is contracted more forcefully, more and more muscle fibers are activated, producing action potentials.

A related procedure that may be performed is nerve conduction velocity (NCV). NCV is a measurement of the speed of conduction of an electrical impulse through a nerve. NCV can determine nerve damage and destruction, and is often performed at the same time as EMG. Both procedures help to detect the presence, location, and extent of diseases that damage the nerves and muscles. For example cervical or lumbar radiculopathy, Peripheral nerve deficits, Sciatica nerve pain cubital tunnel syndrome and carpal tunnel syndrome etc.

 
EMG/NCV Patient pre-test instructions


Things to tell the doctor prior to the test:

  1. Are you on blood thinners like conmadin, aspirin or heparin?
  2. Do you have a pacemaker?


Instructions to patient before doing test:

  1. Don't put oil, cream or lotion to the body or extremities.
  2. Don't shave the legs prior to the test.
  3. Tell the doctor if you are sensitive to electric current or have a fear of needles.


The approximate testing time required is as listed below:

  1. Upper extremity is about one hour (60 mins). 
  2. Lower extremity is about one and one half hours (90 mins).
  3. Both upper and lower extremities about two and one half hours (150 mins).