Nerve and muscle disorders cause the muscles to react in abnormal ways. Measuring the electrical activity in muscles and nerves can help detect the presence, location and extent of diseases that damage muscle tissue (such as muscular dystrophy) or nerves (such as amyotrophic lateral sclerosis: Lou Gehrig's disease). In the case of nerve injury, the actual site of nerve damage can often be located. In a clinical setting, EMG and nerve conduction studies are usually done together.