Also called a nerve conduction study (NCS), the test finds out how fast an electrical impulse moves through the nerve. Healthy nerves transmit electrical signals more rapidly than damaged nerves. It allows your doctor to differentiate between a nerve disorder and a condition where a nerve injury has affected the muscles. Your doctor may advise this test to diagnose carpal tunnel syndrome, cubital tunnel syndrome, Charcot-Marie-Tooth (CMT) disease, herniated disc disease, and muscle disorders.