There are several other names which have been used to describe similar syndromes. Myofascial pain is an important component of other pain syndromes. If you have arthritis, and are protecting your hands, you may strain your neck or shoulders. If you have post-herpetic neuralgia, or another condition with increased sensitivity of the skin, you have probably made certain changes in the way you move. Your body will work to reduce a particular pain, though this may put strain on the upper and lower back.
Back pain is an example where muscular pain can be a major contributor.
And discs can be slipped without causing any pain at all. But there are large amounts of muscle in the back which are continually susceptible to injury, causing back or even leg pain. Often, people who have pain, do not even realize when it is coming from the muscles. Or, people who have pain do not realize that painful muscles are making their symptoms worse. Muscles are injured by both sudden strains, and repetitive injury over the years.