Myalgia also called muscle ache is the medical term for muscle pain. Myalgia is a symptom of many diseases. The most common cause of acute myalgia is the overuse of a muscle or group of muscles; another likely cause is a viral infection, especially when there has been no trauma. The most common causes of myalgia are overuse, injury, and strain. Myalgia might also be caused by allergies, diseases, medications, or as a response to vaccination.