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Electromyography (EMG) is an electrical recording of muscle activity that aids in the diagnosis of neuromuscular disease.


Muscles are stimulated by signals from nerve cells called motor neurons. This stimulation causes electrical activity in the muscle, which in turn causes contraction. This electrical activity is detected by a needle electrode inserted into the muscle and connected to a recording device. Together, the electrode and recorder are called an electromyography machine. EMG can determine whether a particular muscle is responding appropriately to stimulation, and whether a muscle remains inactive when not stimulated.
EMG is performed most often to help diagnose different diseases causing weakness. Although EMG is a test of the motor system, it may help identify abnormalities of nerves or spinal nerve roots that may be associated with pain or numbness. Other symptoms for which EMG may be useful include numbness, atrophy, stiffness, fasciculation, cramp, deformity, and spasticity. EMG results can help determine whether symptoms are due to a muscle disease or a neurological disorder, and, when combined with clinical findings, usually allow a confident diagnosis.
EMG can help diagnose many muscle and nerve disorders, including:
  • muscular dystrophy
  • congenital myopathies
  • mitochondrial myopathies
  • metabolic myopathies
  • myotonias
  • peripheral neuropathies
  • radiculopathies
  • nerve lesions
  • amyotrophic lateral sclerosis
  • polio
  • spinal muscular atrophy
  • Guillain-Barré syndrome
  • ataxias
  • myasthenias


No special precautions are needed for this test. Patients with a history of bleeding disorder should consult with their treating physician before the test. If a muscle biopsy is planned as part of the diagnostic work-up, EMG should not be performed at the same site, as it may effect the microscopic appearance of the muscle.


During an EMG test, a fine needle is inserted into the muscle to be tested. This may cause some discomfort, similar to that of an injection. Recordings are made while the muscle is at rest, and then during the contraction. The person performing the test may move the limb being tested, and direct the patient to move it with various levels of force. The needle may be repositioned in the same muscle for further recording. Other muscles may be tested as well. A typical session lasts from 30-60 minutes.
A slightly different test, the nerve conduction velocity test, is often performed at the same time with the same equipment. In this test, stimulating and recording electrodes are used, and small electrical shocks are applied to measure the ability of the nerve to conduct electrical signals. This test may cause mild tingling and discomfort similar to a mild shock from static electricity. Evoked potentials may also be performed for additional diagnostic information. Nerve conduction velocity and evoked potential testing are especially helpful when pain or sensory complaints are more prominent than weakness.


No special preparation is needed. The doctor supervising and interpreting the test should be given information about the symptoms, medical conditions, suspected diagnosis, neuroimaging studies, and other test results.


Minor pain and bleeding may continue for several hours after the test. The muscle may be tender for a day or two.


There are no significant risks to this test, other than those associated with any needle insertion (pain, bleeding, bruising, or infection).

Normal results

There should be some brief EMG activity during needle insertion. This activity may be increased in diseases of the nerve and decreased in long-standing muscle disorders where muscle tissue is replaced by fibrous tissue or fat. Muscle tissue normally shows no EMG activity when at rest or when moved passively by the examiner. When the patient actively contracts the muscle, spikes (motor unit action potentials) should appear on the recording screen, reflecting the electrical activity within. As the muscle is contracted more forcefully, more groups of muscle fibers are recruited or activated, causing more EMG activity.

Abnormal results

The interpretation of EMG results is not a simple matter, requiring analysis of the onset, duration, amplitude, and other characteristics of the spike patterns.
Electrical activity at rest is abnormal; the particular pattern of firing may indicate denervation (for example, a nerve lesion, radiculopathy, or lower motor neuron degeneration), myotonia, or inflammatory myopathy.
Decreases in the amplitude and duration of spikes are associated with muscle diseases, which also show faster recruitment of other muscle fibers to compensate for weakness. Recruitment is reduced in nerve disorders.



Falck, B., E. Stalberg, and L. Korpinen. The Expert Electromyographer. 〈http://www.tut.fi/∼korpinen/EMG.htm〉.

Key terms

Motor neurons — Nerve cells that transmit signals from the brain or spinal cord to the muscles.
Motor unit action potentials — Spikes of electrical activity recorded during an EMG that reflect the number of motor units (motor neurons and the muscle fibers they transmit signals to) activated when the patient voluntarily contracts a muscle.


the recording and study of the intrinsic electrical properties of skeletal muscle. adj., adj electromyograph´ic. When it is at rest, normal muscle is electrically silent, but when the muscle is active, an electrical current is generated. In electromyography the electrical impulses are picked up by needle electrodes inserted into the muscle and amplified on an oscilloscope screen in the form of wavelike tracings. The visual recording may be accompanied by auditory monitoring in which the sounds are amplified.ƒ

Electromyography is useful in diagnosing disorders of the nerves supplying the muscle (as in amyotrophic lateral sclerosis and poliomyelitis) and in disorders affecting the muscle tissues. Recordings usually are obtained while the muscle is relaxed, during voluntary contraction, and during muscle activity that is produced by nerve stimulation. In this way it is possible to determine the presence of a disorder, localize the site, and identify the specific disease producing muscle weakness.


1. The recording of electrical activity generated in muscle for diagnostic purposes; both surface and needle recording electrodes can be used, although characteristically the latter is employed, so that the procedure is also called needle electrode examination.
2. Umbrella term for the entire electrodiagnostic study performed in the EMG laboratory, including not only the needle electrode examination, but also the nerve conduction studies.
[electro- + G. mys, muscle, + graphō, to write]


EMG Neurology A technique that measures minute electrical discharges produced in skeletal muscle, at rest and during voluntary contraction; EMG is used to diagnose neuromuscular disease; the electrode for EMG is inserted percutaneously and the resulting electrical discharge or motor unit potential is recorded


(EMG) (ĕ-lek'trō-mī-og'ră-fē)
1. The recording of electrical activity generated in muscle for diagnostic purposes; both surface and needle recording electrodes can be used; the latter are more common.
2. Umbrella term for the entire electrodiagnostic study performed in the EMG laboratory, including not only the needle electrode examination, but also nerve conduction studies.
[electro- + G. mys, muscle, + graphō, to write]


A diagnostic method in which the electrical events associated with muscle contraction are amplified and recorded for analysis. The signals may be picked up by surface electrodes or a needle consisting of two insulated, coaxial conductors may be pushed into the muscle. The method allows distinction to be made between various nerve disorders, disorders affecting the junction between the nerve and the muscle and various muscle disorders.


(EMG) (ĕ-lek'trō-mī-og'ră-fē)
1. Recording of electrical activity generated in muscle for diagnostic purposes.
2. Umbrella term for the entire electrodiagnostic study performed in the EMG laboratory, including not only needle electrode examination, but also nerve conduction studies.
[electro- + G. mys, muscle, + graphō, to write]
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The effect of forward walking and backward walking on quadriceps muscles with treadmill inclination: surface electromyographic analysis.
(1994) Electromyographic analysis of knee rehabilitation exercises.
The objective of this study was to evaluate the electromyographic activity of the supra-hyoid muscles during deglutition in participants with Angle's Class II, division 1 malocclusion.
Electromyographic analysis of knee push up plus variations: what's the influence of the kinetic chain on scapular muscle activity?
Electromyographic reliability and analysis of selected lower extremity muscles during lateral step-up conditions.
The purpose of the present study was to analyze the levels of localized muscle fatigue by means of the electromyographic signal, as well as to use the [f.sub.med] to estimate the recovery rate of the rectus femoris and biceps femoris muscles that are constantly in use by handball players.
Electromyographic findings of voluntary muscle contraction, recruitment of muscle units and spontaneous potentials were supportive in such pathological differentiation.
Early investigation of the electromyographic characteristics of children could facilitate the development of treatment strategies aimed at normalizing muscle activity so as to achieve functional improvement in these patients.
Electromyographic analysis of masticatory and neck muscles in subjects with natural dentition, teeth-supported and implant-supported prostheses.
The next generation SedLine enhances the PSI to make it less susceptible to electromyographic (EMG) interference and to improve performance in low-power EEG cases.
The reliability of surface electromyographic (sEMG) variables during swallowing determines the potential usefulness of these measures in swallowing assessment and treatment.