This study will investigate problems with muscle weakness and control using electromyography-a test of nerve-muscle cell communication. Advanced techniques called single fiber electromyography and macro-electromyography, which evaluate individual muscle fibers, will be used. Besides aiding in diagnosis, these tests provide information about disease progression that may be useful in guiding therapy.

Adult patients with suspected neurological disorders of muscle control and weakness may be eligible for this study. Normal volunteers may also participate. For the electromyography procedure, a special needle is inserted into a muscle. The patient will slightly tense the muscle and maintain the tension while electrical signals from the muscle fibers are being recorded. The electrical signals are played through a loudspeaker, providing feedback to help the patient tense the muscle the appropriate amount. The test, which is usually done for only one muscle, takes 1 to 2 hours. If needed, short breaks can be taken.

If the patient cannot maintain tension in the muscle for the entire test period, a nerve will be stimulated to activate the muscle. A thin needle is inserted near the nerve, and a series of small electrical shocks are given to activate a nerve fiber. The electromyography needle is inserted into the muscle to measure the response, as described above.

A neurologist receiving specialized training in clinical neurophysiology will do the electromyography procedure under the direct supervision of an experienced neurologist.