EMG Test: What It Is, How It Feels and Results

01The test

What an EMG test measures

Muscles contract when nerve cells called motor neurons send them electrical signals. As muscles tighten, they produce electrical activity of their own that can be measured. Mayo Clinic explains that an EMG uses tiny devices called electrodes to translate these signals into graphs, sounds or numerical values, which are then interpreted by a specialist.

MedlinePlus explains that a healthy muscle should not give off electrical signals when it is at rest. If a muscle is damaged, it may show electrical activity at rest, or abnormal activity when it is used. EMG results can therefore reveal problems in the nerve, in the muscle or in the transmission of signals from nerve to muscle.

02Reasons

Why a doctor may request it

According to Mayo Clinic and MedlinePlus, a doctor may order an EMG if you have symptoms that could point to a nerve or muscle disorder, such as:

• tingling or numbness in the arms, legs, hands, feet or face
• muscle weakness
• muscle pain, cramps, spasms or twitching
• certain types of limb pain
• paralysis of any muscles

Mayo Clinic adds that EMG results are often needed to help diagnose or rule out conditions such as muscle disorders, diseases affecting the connection between nerve and muscle, disorders of the nerves outside the spinal cord such as carpal tunnel syndrome, disorders of the motor neurons in the brain or spinal cord, and problems with a nerve root, such as a herniated disk in the spine.

03Two parts

Needle EMG and surface electrodes

Mayo Clinic describes two parts of the study. In a needle EMG, a needle electrode inserted directly into a muscle records the electrical activity in that muscle. In a nerve conduction study, electrode stickers applied to the skin (surface electrodes) measure the speed and strength of signals traveling between two or more points along a nerve.

MedlinePlus explains that the two tests can be done separately, but are usually done at the same time; when both are done, the nerve conduction study is done first. Together, they help tell whether symptoms come from a muscle or a nerve disorder. The muscles and nerves examined depend on where your symptoms are, so the number of needle insertions varies from person to person.

04Preparation

How to prepare: skin, medicines and devices

Mayo Clinic and MedlinePlus give similar preparation advice:

• shower or bath shortly before the test to remove oils from your skin, and do not apply lotions, creams or perfumes beforehand, as they can change the results
• wear loose, comfortable clothing that gives easy access to the area being tested
• tell the team if you have a pacemaker, cardiac defibrillator or any other electrical medical device, as special steps may be needed
• tell them if you take blood-thinning medicines or have a bleeding disorder such as hemophilia
• when you book, ask whether you need to stop any prescription or over-the-counter medicines before the test

Mayo Clinic notes that people who take pyridostigmine, a medicine used for myasthenia gravis, should specifically ask whether it should be paused for the test. Do not stop blood thinners or any other medicine on your own: the decision belongs to the doctor who prescribes them and the team doing the test.

05Procedure

What happens during the test, step by step

You may be asked to change into a gown and sit or lie on an examination table. For the needle part, MedlinePlus explains that the skin over the muscle is cleaned and a small needle electrode is placed in the muscle. The machine records activity while the muscle is still, and then while you tighten it slowly. The electrode may be moved to record activity in different muscles.

During the needle EMG, Mayo Clinic explains that the specialist looks for spontaneous electrical activity at rest, which is not present in healthy muscle, and at the degree of activity when you slightly contract the muscle. You will be told when to relax and when to tighten, and you may be asked to change position. The activity is shown on a screen as wavy and spiky lines and may also be played through a speaker as popping sounds.

06Comfort

What it feels like and how long it takes

MedlinePlus explains that you may feel slight pain or discomfort when the needle electrode is inserted, and a tingling feeling, like mild static electricity, during the nerve conduction part. Mayo Clinic notes that needle discomfort usually ends shortly after the needle is removed, and that the small pulses from surface electrodes may be felt as a twinge or spasm.

How much it bothers people varies. If the discomfort becomes very uncomfortable, say so: MedlinePlus notes this may affect the results, and Mayo Clinic suggests asking for a short break. MedlinePlus gives 30 to 60 minutes for an EMG and 15 minutes to over an hour for a nerve conduction study, depending on how many nerves and muscles are tested.

07Aftercare

Aftercare and possible soreness

Mayo Clinic describes EMG as a low-risk procedure with rare complications. There is a small risk of bleeding, infection and nerve injury where the needle is inserted. When muscles of the chest wall are examined, there is a very small risk of air leaking around the lung and causing it to collapse (pneumothorax).

MedlinePlus notes that the muscles tested may be sore for a few days and that small bruises may appear where the needles were placed. Mayo Clinic advises contacting your doctor if bruising persists beyond several days. Sudden chest pain or breathlessness after a test of the chest muscles needs urgent medical attention.

08Results

How results are interpreted with your symptoms

The specialist who performs the EMG interprets the recordings and prepares a report. Mayo Clinic explains that the doctor who ordered the test then discusses the report with you at a follow-up appointment. The timing of results depends on the service.

MedlinePlus lists conditions that abnormal results may point to, depending on which nerves or muscles are affected, including carpal tunnel syndrome, a herniated disk, Guillain-Barré syndrome, myasthenia gravis, muscular dystrophy, Charcot-Marie-Tooth disease and amyotrophic lateral sclerosis (ALS). It stresses that to understand the results, the doctor will consider your symptoms, medical history and other test results.

09Sources

Where the sources differ

Both sources agree on what the test measures, how to prepare and what it may feel like. Mayo Clinic’s page (May 2019) is older and gives more detail on risks, including the rare pneumothorax with chest wall muscles and the question of pausing pyridostigmine. MedlinePlus (April 2024) adds approximate durations, the order of the two tests and a list of conditions linked to abnormal results.

Neither source says that an abnormal EMG equals one specific disease, or that a normal EMG rules out every nerve or muscle problem. An EMG answers a question asked by your doctor and is read together with your history, examination and other tests. If your doctor has requested an EMG or nerve conduction study, our clinical neurophysiology service in Bilbao performs these tests and explains what will be examined and why (consultations are in Spanish); diagnosis and treatment remain with your referring doctor.

10Summary

In summary

An EMG records the electrical activity of muscles at rest and during contraction, usually together with a nerve conduction study that measures how signals travel along nerves. It is requested for symptoms such as numbness, tingling, weakness or cramps. Prepare with clean skin and no creams, and tell the team about electrical devices, blood thinners and bleeding disorders. Mild discomfort and a few days of soreness or bruising are common.

Before the test, it helps to write down a few questions: which muscles and nerves will be studied, which question the test is meant to answer, and how and when you will receive the results. Results are interpreted together with your symptoms and other tests.