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Review of Mechanisms and Assessment of Muscle Pain

Scientists around the world are studying pain mechanisms of all kinds. In this article, the characteristics and causes of muscle pain are reviewed. Methods used to conduct experiments to better understand pain are explained.

For example, muscle pain can be evoked by internal versus external sources. Ischemia (decreased blood flow) and exercise are two ways to induce muscle pain. Electrical stimulation and mechanical and chemical causes of muscle pain are also discussed.

Exploring the causes and effects of muscle pain in an experimental fashion has shown researchers many new things. For example, muscle hyperactivity is not caused by muscle pain in the normal adult. But for someone with chronic musculoskeletal pain, increased electrical activity has been measured in the muscles. This occurs both at rest and after activity.

Recent studies have shown us that muscle pain can alter motor control. Muscle pain can cause changes in muscle coordination and changes in motor strategies. The exact effects depend on the specific motor task.

Maximal muscle contractions are less in people with muscle pain. But this is not as a result of changes in the muscle fibers. It appears to be a central effect. That means there has been a change in the motor control function (not in the muscle itself). Messages from the brain and/or spinal cord result in fewer motor units firing.

At the same time, muscle activity of other muscles that work together with the primary (painful) muscle are also inhibited. As a result, tenderness and referred pain in chronic musculoskeletal disorders are common.

The new information that motor control is affected by muscle pain has been a major breakthrough discovery. Experimental models of muscle pain will continue to help us understand how and why pain becomes chronic. Finding clues to stop pain messages is the desired effect. New treatment interventions for chronic pain may be the final outcome.

References: Lars Arendt-Nielsen, PhD, Dr Med Sci, and Thomas Graven-Nielsen, PhD, Dr Med Sci. Muscle Pain: Sensory Implications and Interaction with Motor Control. In Clinical Journal of Pain. May 2008. Vol. 24. No. 4. Pp. 291-298.

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