An EMG is done to help diagnose diseases that damage muscle tissue, nerves, or the junctions between nerve and muscle. This diagnostic test can help find the cause of weakness, paralysis, or muscle twitching. EMG measures the electrical activity of muscles at rest and during contraction. Nerve conduction studies measure how well and how fast the nerves can send electrical signals. This diagnostic test is done to find damage to the peripheral nervous system, which includes all the nerves that lead away from the brain and spinal cord and the smaller nerves that branch out from those nerves.