Electromyography (EMG) is useful in diagnosing and assessing many neuromuscular conditions, including—perhaps most commonly—back pain. It can be performed in one of two ways: attaching an electrode pad to the surface of the skin or inserting a needle electrode through the skin. The electrodes transmit and detect electrical signals and analyze the electrical activity associated with muscle contraction. An EMG study then translates the data into graphs and charts. When muscle tissue is at rest, it normally does not show any electrical activity. However, when muscle contracts, action potentials—which are short-lasting events in which a cell’s electrical membrane potential quickly spikes and then falls—begin to appear. Doctors often order EMGs when patients are experiencing tingling, numbness, pain, or weakness in their muscles and/or limbs. The main reason for completing an EMG study is to determine whether a muscle is active or inactive. It also can be used to measure muscle fatigue or to diagnose neuropathies, neuromuscular junction diseases, and myopathies—including muscular dystrophy, polymyositis, carpal tunnel syndrome, amyotrophic lateral sclerosis, polio, or herniated disks. While EMG testing is a relatively low-risk procedure, there is a very small risk of nerve injury, bleeding, or infection at the site of electrode insertion. There may be certain procedural restrictions for patients who have pacemakers or similar devices; take blood-thinning medications; or have any blood-clotting disorders, including hemophilia.