While the exact cause of myofascial pain is unknown, there are some working theories that may explain the symptoms of the disease. Muscle injury or repetitive strain may be an underlying cause, which activate myofascial trigger points. Psychological stressors and physical strain may also increase muscle tension along fibers referred to as the taut band, a hardened ropelike stretch of muscle fibers in which triggers are present. Myofascial pain may also originate from postural stressors, such as poor body posture at a desk, held for prolonged periods.
The word "myofascial" comes from "myo," meaning muscle tissue, and "fascia," the connective tissue in and surrounding the muscles. When a trigger point within the muscle is activated, the muscle fibers contract. The resulting sensation from trigger point activation may take the form of referred pain or pain in an area other than the point of origin. For example, a trigger in the trapezius muscle, which helps raise the shoulder, can shoot pain up the shoulder to the neck and head and can be experienced as a headache.
It is believed that active muscle trigger points can be formed in several ways:
- repetitive overuse injury
- habitual poor posture
- direct injury
- sustained heavy lifting
- regular muscle tension and clenching as shown in the image to the right
- prolonged inactivity
When a trigger point becomes active due to injury or irregular use, the muscle fibers containing that trigger point tighten to create a taut band that keeps the muscle in a continuously contracted state. The muscle, in turn, becomes weak and inflexible and may even trap adjacent nerves, leading to secondary pain sensations, such as numbness and aching. If left untreated, surrounding muscles may eventually become overworked as they make up for the affected muscle's inefficiencies. These overstressed muscles may then develop trigger points as well, creating complex networks of referred pain and myofascial pain patterns.
Trigger points may also be present within the muscle structure in a latent state. In these cases, discomfort is felt primarily if pressure is applied directly to the trigger point. A latent trigger point can become active if the muscle in which it resides is aggravated due to injury, overuse, illness or stress.