Muscle pain: sensory implications and interaction with motor control.

Muscle hyperalgesia and referred pain plays an important role in chronic musculoskeletal pain. New knowledge on the involved basic mechanisms and better methods to assess muscle pain in the clinic are needed to revise and optimize the treatment regimes. Increased muscle sensitivity is manifested as (1) pain evoked by a normally non-nociceptive stimulus (allodynia), (2) increased pain intensity evoked by nociceptive stimuli (hyperalgesia), or (3) increased referred pain areas with associated somatosensory changes. Quantitative sensory testing provides the possibility to evaluate these manifestations in a standardized way in patients suffering from musculoskeletal pain or in healthy volunteers. Some manifestations of sensitisation, such as expanded referred muscle pain areas in chronic musculoskeletal pain patients, can be explained from animal experiments showing extrasegmental spread of sensitisation. An important part of the pain manifestations (eg, tenderness and referred pain) related to chronic musculoskeletal disorders may be due to peripheral and central sensitization, which play a role in the transition from acute to chronic pain. In recent years, it has become evident that muscle pain can interfere with motor control strategies and different patters of interaction are seen during rest, static contractions, and dynamic conditions.