All You Need To Know About Electromyography.


What is Electromyography (EMG)?

Electromyography (EMG) measures the muscle action or electrical activity in response to a nerve’s stimulation within selected muscle fiber in our muscle. Our muscles move when nerve received signals from the brain.

Electromyography test will measures how well our muscles in response to those signals. This test may help differentiate between a muscle disorder and a nerve disorder, which can help the doctor to make an accurate diagnosis.

If the test picks up a problem, we may be diagnosed with what is called a neuromuscular disorder.

During an EMG, a thin and tiny needle as well as electrode is inserted through our skin into a specific muscle. The electrodes will pick up the electrical activity then displays on a monitor in the form of waves. Sometimes an audio-amplifier is employed so the activity can be heard as well. Often, several muscles are tested one at a time, the number and location of muscles will depends on what the doctor is aiming for.


As we relax and contract the muscle, the electrical impulses are recorded on an oscilloscope, a device that displays the electrical impulses in a wave-like pattern. Additionally, the doctor may listen to the results through a speaker with the help of audio-amplifier.

EMG measures the electrical activity of our muscle during rest, slight contraction, and forceful contraction. A brief period of activity can be seen when an electrode is inserted. But after that, there should be no signal. Generally, muscle tissue does not normally make electrical signals during rest, it will only show it when it contracts. But if our muscle is damaged or has lost input from nerves, it may have abnormal electrical activity during rest. Electrical activity may make abnormal patterns when it contracts.

The action potential (size and shape of the wave) that makes by our reflexes or motions will display on the monitor which gives information about how our muscle responds to nerve stimulation. As we contract our muscle more forcefully, more and more muscle fibers are activated, thus making more action potentials.

What is Evoked Potential (EP)?

Evoked potential tests measure the time it takes for the brain to respond to sensory stimulation either through audio, video, or touch.

Doctors use this test to help diagnose multiple sclerosis (MS) and other conditions that can cause a person’s reactions to slow. The test can detect unusual responses toward stimulation.

The body are connected through a series of cells that communicate with electrical signals by the nervous system. When the body receives stimulation, electrical signals will reach the nervous system to the brain through the fatty layer of myelin that protects the nerve cells.

Stimulation can either be visual, capturing through the eyes, auditory, listening through the ears or somatosensory stimulation or touch, when sensations reaches the skin. When we see an object, for example a drain is right in front of us and the image captures and stimulates the sensory receptors in our eyes. The receptors then send the electrical signals to the brain for processing in order to decide the next step we should take is either to turn around or jump across the drain.

The signal that image stimulates arrives to the brain are slower than one that touch stimulates. The reason behind this mechanism is due to when we sees an image, the body must first convert the image into an electrical signal before sending it to the brain for processing.

Unfortunately, there are some medical conditions that affect this signaling time, resulting in an unusually slow response time, causing massive inconveniences and which sometimes could be lethal in certain situations. One of the well known medical conditions that falls under this category is Multiple Sclerosis.

MS occurs when the immune system damage the fatty layer of myelin sheath that coats and protects nerve cells fiber in the brain and spinal cord. This damage affects the speed of the electrical signals to travel across the nerve cells.

What is Nerve Conduction Velocity (NCV)?

A nerve conduction velocity (NCV) test is also known as a nerve conduction study, it is used to assess nerve damage and dysfunction. The procedure will measure the speed of electrical signals to travel through our peripheral nerves.

Our peripheral nerves are located outside of our brain and along with our spinal cord. These nerves help us control our muscles and experience different senses. Healthy nerves tend to send electrical signals more quickly and with greater strength compare to the damaged nerves.

The NVC test helps our doctor to differentiate between an injury to the nerve fiber and an injury to the myelin sheath, the coats and protective layer covering surrounding the nerve cells. It can also help our doctor to tell the difference between a nerve disorder and a condition where a nerve injury has affected the muscles.

During an NCV, patch-like electrodes are applied to our skin in several desired places over the nerve to be tested. Low-level electricity is then dispensed through the electrodes in order to stimulate the nerve. The amount of the output of the electricity is similar to a shock from static electricity. The screen will displays and measures the velocity at which the electrical signal flows through the nerve.

Nerve signals are electrical signals that travel quickly throughout our nervous system. Sometimes, the problems with the electrical activity in our nerves can cause pain, tingling, or weakness in our muscles.