Impact of clinical and experimental pain on muscle strength and activity.

A reorganized motor control system is a key factor in musculoskeletal pain conditions, and its relevance in the transition from acute pain to chronic pain is most likely underestimated. The interaction between muscle pain and motor control depends on the specific motor task. Muscle pain causes no increase in electromyographic activity at rest and reduces maximal voluntary contraction and endurance time during submaximal contractions. Furthermore, muscle pain causes an adaptive change in the coordination during dynamic exercises. Increased muscle activity reflecting reorganized muscle coordination and strategy is also a component of the functional adaption to muscle pain. In general, the "vicious cycle" hypothesis is not supported by these findings. Instead, they support an adaptive model predicting reduced agonistic muscle activity eventually advanced by changed antagonistic muscle activity. The motor control assessment procedures provide complementary clinical information and give further support for optimizing treatment regimens and prevention procedures for musculoskeletal pain.