Electromyogram (EMG) and nerve conduction studies measure electrical activities in the muscles. An electromyogram (EMG) analyzes electrical activity when the muscles are in use and at rest, while a nerve conduction study measures how quickly and efficiently the nerves in muscles send electrical signals. These diagnostic tests may be administered to patients suffering from leg pain or numbness. An EMG is usually done to find problems that may damage muscle tissue and nerves, such as herniated discs or amyotrophic lateral sclerosis (ALS). Alternatively, a nerve conduction study is usually done to identify problems within the peripheral nervous system. Results from the studies may take two to three days to complete.