Myofascial pain syndromes
Pain syndromes of suspected myofascial origin are one of the most prevalent problems in clinical neurology today. These syndromes include tension headache, temporomandibular pain, myofascial pain relating to hyperextension injury (‘whiplash’) or located to muscles such as sternocleidomastoid or trapezius, as well as subgroups of chronic low back pain. Many of these conditions are located to cervical or suboccipital muscles and constitute a separate group in the classification scheme for chronic pain published in Pain (Merskey, 1986). The pain appears to originate in muscles or connective tissue associated with muscle. The aetiology is not known, but parameters indicating a negative emotional state (depression, anxiety), stressful conditions at home or at work (time pressure, emotional conflicts, perceived poor psychosocial work environment) or mechanical stress (posture, repetitive work tasks) are often shown to correlate with the pain condition (Holm et al., 1986; Ellertsen & Kløve, 1987; Kamwendo, Linton & Moritz, 1991; Winkel & Westgaard, 1992).
Myofascial pain syndrome in the trapezius muscle is often caused by mechanical stressors at the work place, such as maintained postures or repetitive work tasks. The trapezius muscle is particularly vulnerable in its function as a stabilizer of the scapula and lifter of the shoulder girdle. In this research area work tasks demanding a high level of muscle force, causing muscle fatigue with a feeling of discomfort and presumably causing muscle pain in the longer term, were initially studied.