Electromyography

What is Electromyography?

Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect medical abnormalities, activation level, recruitment order or to analyze the biomechanics of human movement.

EMG is an outpatient procedure that usually takes about 30-60 minutes. During an EMG, your physician will test nerve function by applying small electrical impulses to specific nerves and measure their response. Then a small, thin needle is placed into the muscle to record the electrical activity during relaxation and contraction. EMG tests involve no radiation or medication and are very safe. You may experience slight discomfort during the test and your muscles may be a bit sore following the procedure, but there are no long-term side effects.

Why the Test is Performed:

EMG is most often used when people have symptoms of weakness, and examination shows impaired muscle strength. It can help to tell the difference between muscle weakness caused by injury of a nerve attached to a muscle and weakness due to neurologic disorders.

Disorders or Conditions Causing Abnormal Results:

An EMG can detect problems with your muscles during rest or activity. Disorders or conditions that cause abnormal results include the following:

Alcoholic neuropathy
Amyotrophic lateral sclerosis (ALS)
Axillary nerve dysfunction
Becker's muscular dystrophy
Brachial plexopathy
Carpal tunnel syndrome
Cervical spondylosis
Common peroneal nerve dysfunction
Denervation (reduced nerve stimulation of a muscle)
Dermatomyositis
Distal median nerve dysfunction
Duchenne muscular dystrophy
Facioscapulohumeral muscular dystrophy (Landouzy-Dejerine)
Familial periodic paralysis
Femoral nerve dysfunction
Friedreich's ataxia
Guillain-Barre syndrome
Lambert-Eaton syndrome
Mononeuritis multiplex
Mononeuropathy
Myopathy (muscle degeneration caused by a number of disorders, including muscular dystrophy)
Myasthenia gravis
Peripheral neuropathy
Polymyositis
Radial nerve dysfunction
Sciatic nerve dysfunction
Sensorimotor polyneuropathy
Shy-Drager syndrome
Thyrotoxic periodic paralysis
Tibial nerve dysfunction
Ulnar nerve dysfunction

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Electromyography

What is Electromyography?

Why the Test is Performed:

Disorders or Conditions Causing Abnormal Results: