Electromyography (EMG) and Nerve Conduction Velocity (NCV) are tests your doctor may order to measure muscle action potential and nerve conduction. These tests are performed to determine if symptoms (e.g. weakness, sciatica) are caused by a disorder of the muscle or the nerve supply. Both tests may be performed.
An EMG measures muscle response to nerve stimulation and evaluates electrical activity within selected muscle fibers. The test can help to differentiate between a muscle and nerve disorder.
Test Preparation and Performance
There is usually no special preparation required. The patient may lie down or sit during the test. During the test one or more needle electrodes are inserted through the skin into a specific muscle or muscle group. Then the patient may be asked to contract the muscle (e.g. bending the knee).
The muscle contraction causes a waveform to be traced and detected by an oscilloscope. The oscilloscope displays a visual representation of the electrical variations on a CRT screen. The muscle at rest is displayed as inactive (e.g. small wavy line). When the muscle is contracted the waveform spikes denoting electrical activity in the muscle.
Discomfort and Risks
Some discomfort may occur as the needle electrodes are inserted. The muscle(s) tested may feel sore after the EMG.
The risks are minimal. There may be some minor bleeding and there is a small risk of infection where the needle electrodes are inserted.