Myofascial pain syndrome is a chronic type of muscle pain which occurs within sensitive areas of the muscle known as trigger points. The pain is focused in such areas as the pelvis, legs, arms, jaw, lower back, or neck. The area in question may be painful to the touch, with the pain possibly radiating outward through the affected muscle. The pain in question gets progressively worse, in some cases becoming quite severe.
In the wikipedia entry for myofascial pain syndrome (MPS), also known as chronic myofascial pain (CMP), the condition is described as
a syndrome characterized by chronic pain caused by multiple trigger points and fascial constrictions. Characteristic features of a myofascial trigger point include: focal point tenderness, reproduction of pain upon trigger point palpation, hardening of the muscle upon trigger point palpation, pseudo-weakness of the involved muscle, referred pain, and limited range of motion following approximately 5 seconds of sustained trigger point pressure.
For reasons yet unclear, women are more likely to develop MPS than men, and the condition is more common among middle-aged adults than younger adults.