Electromyography (EMG)

Electromyography (EMG) measures the electrical discharges produced in muscles. A thin needle electrode is inserted into the muscle your doctor wants to study. An instrument records the electrical activity in your muscle at rest and as you contract the muscle, such as by bending your arm. The size, duration and frequency of these signals helps determine if there's damage to the muscle or to the nerves leading to the muscle. The test takes about one hour to complete.

A doctor may recommend EMG if you have weakness or numbness. EMG helps evaluate and diagnose muscle and nerve disorders, such as:

• Muscular dystrophy and other muscle disorders (myopathies)
• Peripheral neuropathy
• A pinched nerve (nerve root compression)
• Amyotrophic lateral sclerosis (ALS)

Another part of the EMG is a nerve conduction study. Electrodes are placed on your skin over a nerve that your doctor wants to study. A small electrical impulse is passed through one electrode. An instrument measures the resulting electrical activity, such as the time it takes for the impulse to travel to another electrode. In some nerve disorders, the speed of the signal is dramatically slowed. This test may be used to diagnose peripheral nerve disorders, such as carpal tunnel syndrome.