Electromyography (EMG) is a recording of electrical activity within the muscles after placing a small needle electrode into the muscle. In people, EMG is done fully awake. Since we cannot explain to animals that they might be a little uncomfortable, this procedure is performed under general anesthesia.
There should be no recordable electrical activity in animals that are asleep and not moving. However, in animals with peripheral nerve or muscle disease, EMG often shows abnormal spontaneous electrical activity. EMG is used in combination with nerve conduction velocity testing and muscle/nerve biopsies to help diagnose neuromuscular disorders.