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Understanding Pain, A Ten+ Week Ecourse: Part 8

By Jonathan Blood Smyth

Week 8. Pain and Movement Control

Welcome to the eighth instalment of my Ten+ Week Ecourse, I hope you find it interesting and stimulating.

Part Eight considers the effect pain has on the motor system, the system responsible for our movements and postures. Pain often interferes with what people want to do and the postures they can do it in.

The nerves responsible for movement are very close to the nerves responsible for pain reception and there are strong links between the two. It couldn’t be any other way. When we do something which results in a significant risk to ourselves, it’s our body’s role to move us away from danger.

However, in more long-term pain states, the pain still has strong effects on the movement system, with negative results. If we are going to manage our or others’ pain, we need to know how this fits in.

Dysfunction of the motor/movement system

Changes in movement and other functions such as circulation, temperature and sweating, are common in pain conditions.

The central pain neurons make many connections in the spinal cord which could affect the activity of other nerve groups working in different areas such as movement.

The Flexor Withdrawal Response
We all have this. When you stand on a sharp stone with your bare foot, suddenly your leg comes up towards you and you find you are standing on the other one. The flexor muscles in you leg have responded to a pain input by lifting your leg away from harm.

The development of central sensitization has been shown to be connected to an increase in the withdrawal response. Once it is stimulated, it may remain elevated for days or weeks.

This may be important when we do clinical tests on people who have heightened pain states. Tests such as straight leg raise can bring on the response early in chronic pain sufferers.

A vicious cycle?
Apart from having effects on movement control nerves, pain could also affect the nerves which help regulate the tension which is normally present in our muscles.

One idea that has developed is a kind of vicious cycle being set up in the system. It sounds believable but evidence is not good.

The idea is that the incoming pain excites the nerves which set the tension in the muscle spindles, structures which contribute to the regulation of muscle tension.

Increased activity in the spindle control nerves is thought to lead to increased muscle stiffness. This then leads to increased levels of waste products in the muscle, leading to more muscle stiffness.

However, studies have not shown an increase in muscle electrical activity in these cases, so this idea, while appealing, is not proven to occur.

Adaptation to Pain
This idea, from Lund, suggests a different approach. Incoming pain messages are thought to alter the behaviour of the interconnecting nerves, the nerves which take the incoming messages and pass them on to the necessary places.

This incoming painful stream of messages is thought to inhibit the action of the main moving muscles and increase the actions of opposing muscle groups. Overall this will limit the movement available and reduce its speed.

The result of this should be greater difficulty in getting the muscle concerned to activate, a delay in activation and a degree of weakness.

These kinds of problems have been found in low back pain patients and produced experimentally by injecting salt solution into the back muscles of normal volunteers.

Even though this idea may occur in people with pain, the problems of abnormal movement are likely to be more complex.

Newer ideas

Researchers have gone on to investigate more complicated ideas which may be closer to what happens in reality. The influence of pain on patterns of nerve firing and muscle activity may delay or inhibit key muscle patterns which normally limit movement.

This inhibition is thought to occur mostly in deep muscles which are responsible for joint stability.

The new fashion for core stability and Pilates as the latest exercise craze is partly based on this idea. The deep lumbar stabilizing muscles undergo changes in their effectiveness and control due to pain, but can be helped by targeted muscle work.

This lack of control can continue after the acute pain period and become a chronic problem.

Summary

Tissue damage and acute pain causes alterations in the control and patterns of muscle activity. These abnormalities commonly settle down as the area heals and the pain reduces.

Unfortunately this situation can persist beyond the acute injury phase and become chronic, leading to a long-term problem.

This is an important issue for anyone with pain or anyone trying to help people in pain. The inability to do things is often the most challenging problem facing pain patients. Yes, the pain is a problem, but not being able to do the things you want is often the most distressing part of the situation.

If we are going to help people get over their disability, we have to recognize the altered muscle patterns and the reasons for them. Then we can design a logical strategy to counter the abnormal muscle behaviour and promote normal movement and stability.

Next time we move on to the way pain is integrated and altered in the brain and spinal cord.


Understanding Pain, A Ten+ Week Ecourse by Jonathan Blood Smyth.
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replacement, physiotherapy and pain.
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