Electromyography, or EMG, measures the electrical activity of the nerves that send signals within and between muscles, called motor neurons, and shows a decrease in electrical activity if nerves are damaged, according to Mayo Clinic. Nerves communicate throughout the body with electrochemical signals.
EMG measures and interprets electrical activity via electrodes, and shows the information in visual or audio format. According to Mayo Clinic, there are several methods of assessing electrochemical activity using EMG. A needle electrode directly measures the motor neuron activity within a muscle. A nerve conduction study is used to measure the activity within a specific muscle or along a nerve via electrodes on the skin. A nerve conduction study can show if the motor neurons within a muscle are sending strong or weak signals, and it also assesses signal speed.
Doctors may order an EMG in patients who have nerve pain, muscle spasms or weakness, tingling and numbness. Some conditions that may cause signs of nerve damage include spinal disorders such as herniated discs, peripheral nerve disorders that affect the limbs, and neuromuscular disorders such as muscular dystrophy. EMG testing can show that there is a decrease in nerve signalling and can be used in conjunction with other diagnostic criteria to determine the cause of the damage.