Electromyography (EMG) is a diagnostic exam that evaluates the health of the muscles and the nerves that control them by measuring muscle electrical activity. This test is most commonly performed to determine the cause of muscle weakness and identify cases that are caused by neurologic disorders such as carpal tunnel syndrome, peripheral neuropathy and others rather than primary muscle conditions.
During the EMG exam, thin needle electrodes are inserted through the skin and into the muscle, where they detect electrical activity while the muscle is at rest and contracting. Patients may experience mild pain when the electrodes are inserted, but this is tolerable for most. This test is usually performed in conjunction with a nerve conduction velocity test.
Normal results of an EMG test indicate muscles that do not produce any electrical activity while at rest and progressively increasing with contraction. After the test, patients may experience feelings of tenderness or bruising on the affected muscle.