Overview

Motor neurons transmit electrical signals that cause muscles to contract. An EMG uses tiny devices called electrodes to translate these signals into graphs, sounds or numerical values that are then interpreted by a specialist.

During a needle EMG, a needle electrode inserted directly into a muscle records the electrical activity in that muscle.

A nerve conduction study, another part of an EMG, uses electrode stickers applied to the skin (surface electrodes) to measure the speed and strength of signals traveling between two or more points.

Why is this test for me?

Your doctor may order an EMG if you have signs or symptoms that may indicate a nerve or muscle disorder. Such symptoms may include: tingling, numbness, muscle weakness, muscle pain, or cramping.  EMG results are often necessary to help diagnose or rule out a number of conditions such as:

Muscle disorders such as muscular dystrophy or polymyositis

Diseases affecting the connection between the nerve and the muscle such as myasthenia gravis

Disorders of nerves outside the spinal cord (peripheral nerves) such as carpal tunnel syndrome or peripheral neuropathies

Disorders that affect the motor neurons in the brain or spinal cord such as amyotrophic lateral sclerosis (ALS) or polio

Disorders that affect the nerve root such as a herniated disk in the spine