A myotome is the group of muscles on one side of the body that are enervated by one spinal nerve. A myotome may include parts of muscles.
Doctors use their knowledge of the location of myotomes (and dermatomes) during the physical exam. They perform tests that evaluate loss of strength, disruption of reflexes and loss of feeling in each of the respective myotome or dermatome zones. Testing the myotomes helps the doctor to locate the specific spinal nerve(s) that underlie any loss of movement or physical function you may be experiencing. Testing the dermatomes helps the doctor locate the nerve(s) that give rise to your pain.