Electromyography (EMG) is a diagnostic tool.
The electromyography definition is simply that it is “an electrodiagnostic machine technique for evaluating and recording the electrical activity produced by skeletal muscles”. The tool used is called an electromyograph and the record made is referred to as an electromyogram. When the muscle cells are activated, neurologically or electrically, the electromyography can detect their “electrical potential”. Then the signals are analyzed to find “medical abnormalities, activation level, or recruitment order”, or they can analyze biomechanics. The patient’s skin is prepared by cleansing with alcohol, and then a needle electrode is inserted. The placement of the electrode depends on the size of the muscle and the muscle selected. It is very important to place the needle properly for accuracy, but “EMG is more effective on superficial muscles”. Body fat also interferes with the signal. In fact, the best location for the EMG sensor is “the belly of the muscle: the longitudinal midline”. There does not seem to be a hazard in performing electromyography on patients with implanted defibrillators or pacemakers. There are no known contraindications for performing EMG on patients who are pregnant, either. However, patients with lymphedema are “cautioned to avoid percutaneous procedures in the affected extremity, namely venipuncture”. Although the risks are low, care should be taken to avoid cellulitis or other infections, and any needle examination benefits should be weighed against the potential complications. There are actually two kinds of electromyography. Surface EMG records activity “from the surface above the muscle on the skin”. This provides a limited activity assessment. Fat tissue can affect the recordings, for example. Intramuscular EMG, on the other hand, uses different recording electrodes. It involves using either a concentric or a monopolar needle electrode inserted into the muscle tissue. To get the most accurate picture, the electrode has to be placed in multiple sites. The limitations of this type of EMG are that it involves “voluntary activation of muscle” and is not as useful in certain patients who cannot cooperate (infants, children, and the paralyzed).1
What is Electromyography Used For?
Electromyography can detect if muscle tissue is behaving normally. It should be inactive, electrically, when it is at rest. Only when it is contracted voluntarily should it show action potentials. EMG can also find abnormal results. There are many conditions that can cause those readings, including muscle, nerve, plexus, root, motor neuron, and neuromuscular junction disorders. These include carpal tunnel syndrome, various neuropathies, muscular dystrophy, ALS, and various other conditions. EMG is used, medically, to find neuromuscular diseases, but also for studying kinesiology and detecting “disorders of motor control”. Sometimes electromyography can be used to “guide botulinum toxin or phenol injections into muscles” or as “a control signal for prosthetic devices such as…limbs”. EMG may be useful for “neuromuscular monitoring in general anesthesia”. Electromyography is usually performed with another test that measures nerve functioning. This is NCS, or nerve conduction studies. EMG and NCS are useful tests for when a patient has limb pain, spinal nerve compression weakness, or certain other neurologic disorders or injuries. 2 With NCS, the surfaces electrodes are taped onto the skin to measure the strength and speed of the signals between points.3 The nerve conduction velocity test is “almost always performed during the same visit as the EMG”. These tests are important when patients have abnormal sensations, pain, or weakness. The hope is that these tools can tell whether or not muscle weakness is caused by nervous system disorders, muscle diseases, or injury to a nerve. The test risks are infection or bleeding, but these risks are minimal. Before the test, patients should avoid lotions or creams. In addition, they should, if it is very cold outside, “wait in a warm room for a while before the test”. Any patients who take anticoagulants or blood thinners should tell the practitioner before the exam.4 Smoking should be avoided for at least 3 hours prior to the procedure. While the risks are low, patients may be sore after the exam, and they might have bruising or swelling. Usually the nerve conduction study is performed first, followed by the needle EMG. Patients who have symptoms of numbness, tingling, weakness, cramping, muscle pain, twitching, or paralysis could have muscle disorders (muscular dystrophy), myasthenia gravis, radiculopathies, peripheral nerve disorders (carpal tunnel syndrome), other nerve disorders (ALS), or a herniated disk.5
EMG and Chiropractic
Static and Dynamic Surface Electromyography (sEMG), CLA’s INSiGHT™ scanning technology, can support chiropractic care, according to the Chiropractic Leadership Alliance website. The technology is said to read action potential, or electrical activity, to “measure paraspinal tension, similar to the use of electromyography in EKG/heart rate measurement machines”. Muscles on each side of the spine should be balanced. If they are not balanced, the body compensates, and this uses up energy. The imbalance can be monitored with sEMG, and the technology could “shed light on the muscular changes linked to vertebral subluxations”. With this system, chiropractors can see normal, amplitude (tension), or asymmetry scans, as well as get a dynamic graph to track muscle activity, or the “sEMG-Pattern view…(which) highlights patterns in how energy is distributed throughout the spine and whether this system is efficient or not”. A normal scan will looked “pear-shaped” in the pattern along the spine. The amplitude scan is color-coded to show if a patient is normal (white), if there is mild tension (green), moderate elevation (blue), or high elevation (red). Yellow indicates “below normal amplitude”. The asymmetry scan “depicts the amount of muscle pull from one side to another”. It is also color-coded in the same manner.6