How should an individual with pain arising from muscle be rated using the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides)? Syndromes of muscle pain include simple muscle strains and two controversial conditions, myofascial pain and fibromyalgia. Tables in the AMA Guides can be used for rating forearm injuries that affect grip or pinch strength; a separate set of tables can be used to rate the injury in a lower extremity. Injuries to some muscles (deltoid, biceps, and triceps) are not described in these sections but almost always test as grade 4. Major injury to muscle is well understood and noncontroversial, but terms such as myofascial pain syndrome and fibromyalgia describe controversial muscle pains. Some physicians attempt to differentiate myofascial pain and fibromyalgia on the basis of taut bands in myofascial pain and tender points in fibromyalgia, but the interrater reliability of these findings is low and the consensus view suggests that the cause of these two conditions is unknown. Muscle pain, like muscle contraction headache, irritable bowel syndrome, and dysmenorrhea, are real symptoms for which no impairment rating is provided. Our understanding of these conditions should improve with future research, enabling us to define criteria for evaluating impairment.