Electromyography Systems, Surface and Intramuscular EMG Devices, Nerve Conduction, Muscle Function Testing

What is Electromyography or EMG?

Electromyography, also referred to as EMG, is defined as the recording of the electrical activity of muscle tissue, or its representation as a visual display or audible signal, using electrodes attached to the skin or inserted into the muscle. EMG systems detect the electric potential generated by the muscle cells when they are activated either electrically or neurologically and then produce a record of these signals which is referred to as an electromyogram. This record can then be analyzed in order to detect and diagnose medical abnormalities or to research and analyze the biomechanics of human or animal muscle motion.

Most frequently EMGs are used to identify neuromuscular diseases and disorders of motor control. Examples of conditions diagnosed by EMG are:

• Muscular disorders including things like muscular dystrophy, inflammatory myopathies, or polymyositis
• Diseases affecting the connection between the nerve and the muscle as in myasthenia gravis and botulism poisoning,
• Disorders of the peripheral nerves, or those nerves outside the spinal cord, like carpal tunnel syndrome or peripheral neuropathy
• Disorders that affect the motor neurons in the brain and/or spinal cord which would include conditions like amyotrophic lateral sclerosis or polio
• Disorders that affect the nerve root, examples being cervical, thoracic, lumbar, or sacral radiculopathy (pinched nerve), spinal stenosis, or a herniated disc.

Electromyography tests can be performed with either surface or intramuscular electrodes depending on the patient’s needs and the clinician’s preferences. Surface EMG assesses muscle function by recording the muscle’s activity from outside the skin above the muscle. These readings can be recorded by a pair of electrodes or by a more complex array of multiple electrodes, displaying the potential difference between them. Surface EMG is ideal for recording energy in superficial muscles, closer to the surface of the body, but can be limited by large quantities of body fat and older users with less compliant skin. Intramuscular EMG can be performed with a wide variety of electrode types, but most commonly utilizes stiff, insulated monopolar or concentric needles with a surface electrode for reference in diagnostic procedures. This needle is inserted into the muscle tissue and then moved to multiple spots within a relaxed muscle to evaluate insertional and resting electrical activity in the muscle, then the patient is asked to contract the muscle to test the resulting electrical changes. Intramuscular EMG is ideal for testing both deep and surface muscles, but is limited by its intrusiveness and reliance on patient cooperation and voluntary muscle contraction.