Electromyography, or EMG, measures the muscle's response or electrical activity in response to a nerve's stimulation of the muscle, states John Hopkins Medicine. Doctors use the EMG neurological test to detect neuromuscular abnormalities.
Before an EMG test, the patient needs to remove metal objects, change into a gown, and lie down or sit. After the neurologist has located the muscle he wishes to test, he cleans the skin with an antiseptic solution and inserts one or more needles into the muscle through the skin. He positions a ground electrode under an arm or a leg and may ask the patient to relax or slightly contract or fully contract the muscle.
The needles detect the electrical activity in the muscle, and a monitor displays the results in the form of waves. The size and shape of the wave displayed on the monitor provides information about the ability of the muscle to respond when the nerve stimulates it. The provider measures the electrical activity of the muscle during rest, slight contraction and forceful contraction, according to John Hopkins Medicine. The test may require five or more needle insertions. After the test, the patient may experience some soreness in the muscle.
The doctor may perform the EMG test together with a nerve conduction study or NCS test, notes Johns Hopkins Medicine. The NCS test measures the amount and speed of the conduction of an electrical impulse through a nerve. Doctors use the NCS test to detect nerve damage.