Muscles are suggested to be the most frequent source of the pain in musculoskeletal disorders [11]. The nociceptive afferents, as well as the dorsal horn neurons signaling pain from the muscles, are susceptible to sensitization [12]. The attributes of sensitization are hyperalgesia, but sensitization also implies that innocent mechanical stimuli like touch, muscle contrac- tions, and thermal stimuli are experienced as painful. A high percentage of patients with chronic pain show hyperalgesia, which is enhanced responses to noxious stimulation [13,14]. Sensiti- zation is suggested to be the mechanism behind this increased response and is also of importance for development of chronic pain [15].