Myofascial pain syndrome (MPS), also known as chronic myofascial pain (CMP), is a syndrome characterized by chronic pain in multiple myofascial trigger points ("knots") and fascial constrictions. Characteristic features of a myofascial trigger points 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.