What is electromyography?
Electromyography involves measuring the electrical activity of muscle fibers and recording it as a so-called electromyogram. A distinction is made between:
- Surface EMG: Here, the measuring electrodes are stuck to the skin.
- Needle EMG: Here the doctor inserts a needle electrode into the muscle.
In both cases, the activity of the muscle is measured both during movement and at rest. Based on the type and intensity of the measured activity, the physician can draw conclusions about the origin and extent of a disease.
Electrical muscle activity
If a muscle is to be moved, the brain transmits an electrical impulse via a nerve to the so-called neuromuscular end plate – the “contact point” between a motor nerve and a muscle cell. Here, the impulse releases messenger substances that lead to the opening of ion channels in the membrane of the muscle cell. The resulting ion flow through the membrane creates an electrical voltage: the so-called muscle action potential (MAP) spreads throughout the muscle cell, causing small muscle twitches and can be measured as a potential.
When do you do an electromyography?
In the meantime, electromyography is also used in biofeedback – a special method of behavioral therapy – which can give the patient information about muscle tensions that he does not perceive himself. Thus, he learns to influence them in a targeted manner.
The most common reasons for electromyography are:
- Muscle inflammation (myositis)
- Muscle diseases (myopathies)
- muscle weakness (myasthenia)
- pathologically prolonged muscle tension (myotonia)
What do you do during an electromyography?
The needle EMG begins with the insertion of the electrode into the muscle, which shows up in the electromyogram as a short derivable electrical potential. If no potential is measured, this indicates muscle atrophy. If the potential is significantly prolonged, the physician assumes inflammation or muscle disease.
Muscle activity at rest is then measured. Since a healthy muscle does not emit any electrical impulses, no muscle activity should be measured except for smaller, very short potentials.
Permanent excitation of the muscle can occur if the connection between nerve and muscle is interrupted or the nerve itself is damaged.
In contrast, a surface EMG with adhesive electrodes does not record the individual muscle fibers, but the entire muscle or muscle group. This type of electromyography is mainly used in sports physiology or biofeedback. The electrodes are attached to the skin. The potentials are measured during tension and at rest.
What are the risks of electromyography?
Electromyography is a relatively uncomplicated examination. Because the needle electrode for needle EMG is thinner than a conventional needle, most people feel only a brief prick when it is inserted into a muscle, as with an acupuncture needle. Tightening the muscle may then cause mild pain.
Muscles or nerves are not injured by electromyography. In rare cases, infections or bleeding occur as a result of needle EMG. Therefore, a bleeding tendency should be excluded in advance.
Adhesive electrodes can cause irritation of the skin. A patch allergy is also possible.
What do I have to consider after an electromyography?
You can go home after the outpatient electromyography. If redness or inflammation occurs in the examined body area, please notify your doctor immediately.
