An electromyogram (EMG) measures the electrical activity of muscles when they are relaxed and contracted. Your muscles move when they receive signals from the brain, and an electromyogram measures how well your muscles respond to those signals. During an EMG, a needle electrode is put to a muscle and also attached to a recording machine. Once the electrodes are in place, the electrical activity in that muscle is recorded while the muscle is at rest. Your doctor will ask you to contract the muscle slowly, and that electrical activity is recorded as well. Throughout the test, the electrode may be moved a number of times to assess the activity in different parts of the muscle or in different muscles altogether.
This test helps to diagnose neuromuscular disorders. Your doctor may order an EMG if you have signs or symptoms of a nerve or muscle disorder, which may include tingling, numbness, muscle weakness, muscle pain, or cramping.