Understanding Chronic Pain

Understanding chronic pain and pain systems

This article aims to help you understand more about: 

  • The two types of pain, acute and chronic
  • Pain systems in the body
  • The different theories of pain, including the Gate Control Theory of Pain

Understanding chronic pain

Chronic pain problems are very common. As many as 1 in 7 people are affected by chronic pain, often in different parts of their bodies. Pain is a very personal experience and only you really know how your own pain feels. It can be difficult to find words to describe it to other people. This can make it hard for them to understand how distressing your pain is for you.

Think about how you would describe your pain to someone. For instance, you might use words that describe the pain sensation, such as ‘sharp’, ‘shooting’, ‘nagging’ or ‘aching’. Or you might use words to describe how it makes you feel, such as ‘worried’, ‘scared’, ‘angry’, ‘down’, ‘guilty’ or ‘fed up’. You might also include phrases describing what you think about your pain such as: 

  • I knew I shouldn’t have lifted that heavy container at work.
  • Pain means I’ve been injured. It hurts, so I shouldn’t move.
  • Headaches run in my family. I knew I would get them some time.
  • Bad backs never get better.
  • It’s a damaged nerve after the shingles. It must be serious!

You might also say that you have to do things differently or stop doing activities.

  • I am unable to bend and pick things up from the floor.
  • It alters the way I move – I walk much more stiffly.
  • The pain makes me lie down more often.
  • It stops me going out with friends.
  1. Look at the pain diagram below - picture 1 - and circle the words that describe your pain.
  2. Add any other words that you use to describe your pain.
  3. Add a new branch to the diagram if you need to.

chronic pain mindmap diagram

Pain affects you as a person in many ways. Look at the impact of pain diagram below - picture 2. Add anything to it that you think has been missed out.

chronic pain - the impact of pain mindmap


Acute and chronic pain

A worldwide group of pain specialists (International Association for Study of Pain (IASP) define pain as:

An unpleasant sensory and emotional experience which is due to actual or potential tissue damage or which is expressed in terms of such damage.

This is the definition most doctors and other health professionals use when assessing pain problems.

Doctors, nurses and physiotherapists used to think that pain systems in the body were very simple. However, we now understand that the experience of pain is much more complex. Current research in pain is focusing on how the body’s pain systems work. This will help doctors find ways to reduce pain levels in the future.

What is acute pain?

If you twist an ankle or slip and fall on your knees you will feel acute pain as the muscles, tendons, ligaments, bones, nerves or skin are damaged. You may see a bruise or swelling, and you may feel a lot of pain at the site where the injury has happened. The body releases chemicals and diverts blood to the area in order to help repair damaged tissue. Most pain symptoms usually reduce over six weeks as tissues heal. Nearly all injured tissues are fully healed at six months.

What is chronic pain?

This is pain that continues for longer than three months and it is not normally associated with damaged tissues. We know that all the body’s tissues, even broken bones, are usually healed after six months. Healthcare professionals believe that this type of pain persists for longer than the usual three-month healing period. This is because the nerves originally carrying the pain messages have developed a ‘memory’ for pain and send persistent unhelpful ‘faulty’ messages about pain. These messages are not a signal that the body is damaged or not healed.

Pain puzzles 

Puzzle 1: Some athletes injured in sports events, or soldiers injured in battle, do not notice or feel pain at the time they are injured.

Puzzle 2: People who have had a limb removed can still experience pain in the limb that is no longer there. This is called ‘phantom limb pain’.

Puzzle 3: A person has trodden on a sharp nail. It looks as if it has gone into his foot. The person is in great distress and pain. The foot x-ray shows that the nail has actually broken off in the sole of his boot and has not entered his foot. The person was in severe pain because he thought it had gone into his foot.

These puzzles show that the body’s pain systems are much more complex than people used to realize. They show pain can be linked to the meaning of the event or situation.

Acute and chronic pain systems

These two systems work very differently and it helps to understand them both.

The acute pain system

This is designed to help the body protect itself from damage or harm. For example, if you lift a very hot pan off the stove or have a very hot drink, the heat can cause pain in your hands or mouth. The pain may make you stop what you are doing, as it may cause injury. For example, you may put down the pan, or sometimes even drop it, to avoid being injured by the painful heat.

Acute pain nerve fibres take the pain message from the injury as fast as possible through the spinal cord to the pain centres in the brain. This is a survival mechanism designed to protect the body so the nerves need to send messages quickly to that part of the body to do something immediately, e.g. remove the hand from the hot pan. These are called ‘A’ nerve fibres (standing for ‘acute fast pain message system’). You can think of this system as being similar to dialling straight through to the emergency services for immediate action.

The chronic pain system

This system works differently from the acute pain system. It sends messages to the pain centres in the brain via another type of pain nerve fibre – ‘C’ fibres (standing for ‘chronic pain system’). These fibres send messages very slowly and repeatedly to several pain centres in the brain.

The brain may interpret these persistent pain messages to mean that the pain problem is still happening and is not finished or healed. Alternatively, the ‘C’ fibres may develop a ‘memory’ for pain experiences, and continue to send pain messages for many months or years after an injury, when healing is complete. These fibres are like a set of traffic lights stuck on red, which cannot switch onto green.

The ‘C’ fibre nerve endings can become very sensitive to movement, hot and cold sensations and chemical changes (like inflammation within the body system). Sometimes if the pain area is touched or moved, they send off many, many pain messages to the brain. The nerves seem to magnify the pain feelings or intensity, or cause other sensations like numbness or tingling.

So there seem to be many problems at different places – in the nerve endings, the nerve fibres and the pain centres in the brain. The important point is that feeling chronic pain does not mean there is any harm or damage happening in the body. These are unhelpful ‘faulty’ messages about pain or body sensations, which the pain centres in the brain treat as if they were accurate.

In addition, scar tissue from healed tissues can become tight and stiff. The pain nerves may be wrapped within this tissue. When moving this part of the body, the lack of flexibility (especially in muscles, tendons or joints) can increase pain messages.

There is some good news. It is possible to increase flexibility in stiff, tight tissues and thereby reduce the pain and its consequences. Gradually stretching and strengthening helps the nerve fibres become less sensitive to movement, enabling you to be more active and in less pain.

The best that doctors and physiotherapists can do is to try to help the person to control the pain, possibly by using medications and other treatments. However, this may only change the pain experience a little or in the short term. Doctors and pain scientists still don’t know enough about chronic pain systems and how to switch off the ‘C’ fibre pain messages. This means it is difficult to change:

  • the memory of pain in the ‘C’ fibres and the pain centres in the brain
  • the increased sensitivity in these nerve endings
  • With acute pain or during a setback, it is sensible to reduce many activities for two or three days, especially if there is a lot of bruising or swelling.
  • Most active sports people reduce their sports activities and have longer rest periods. Then, after two or three days, they gradually start to do more, steadily pacing and planning their increased activities   
  • Rest, especially complete rest in bed, is now believed to cause more problems than it solves, except in certain situations, such as cases of severe multiple injuries, e.g. after a car accident.

Theories of pain

The Gate Control Theory of Pain

In the 1960s, two scientists, called Ronald Melzack and Patrick Wall, carried out research to understand pain systems. They developed the Gate Control Theory of Pain.

According to this theory, there are ‘gates’ in the nerve junctions, spinal cord and pain centres in the brain. These gates open and let pain messages through the pain system, so that we feel pain. They can also close to stop messages going through the system, so that the pain is reduced or stopped.

In the 1970s, it was discovered that the body can make its own pain-relief chemicals. These are called endorphins and they work like the pain-relieving drug, morphine. The endorphins can help close the gate. This may explain why some athletes sometimes do not feel pain, even when they are stretching themselves to the limit while doing their sport. Physical activity increases endorphin levels in the body, giving a feeling of well-being and helping to close the pain gate.

In chronic pain there are no treatments that can shut the gate and keep it closed all the time. However, there are ways to close the gate as much as possible so that fewer pain messages pass through the pain system. The brain can focus on very distracting activities. So, for example, someone scoring a winning goal, can have a painful muscle injury and not be aware of much pain.

You can use the skills described in other articles on this website to gain some control over how much the gate is open or closed. In this way, pain can become more manageable and your life more active.

Other theories of pain

Our understanding about chronic pain and theories about its development are constantly changing. One emerging theory is based on the neuromatrix. This theory helps explain the complex changes that occur in the body’s nerve and sensory system for pain as these systems adapt and evolve to deal successfully with threats. This newer theory helps us understand further why getting good pain relief is so difficult. It explains why there are many different problems in different sites, including the brain’s centres for processing and interpreting pain messages. This theory likens the brain’s pain centres to an orchestra, with different groups of instruments trying to play music without a conductor. It highlights the importance of developing coping skills to manage your activities, moods and unhelpful thinking so that you are in control of the pain and independent, and the pain is not in control of you.

What closes the gate and stops the pain?

Circle those things or activities that you know affect your own gate and add more if you can.  

What opens the gate and lets pain through?

Circle those things or activities that you know affect your own gate and add more if you can.

What other parts of the body can send pain messages?

The human body is a complex, tough structure, designed to heal itself while still being active. Our bodies are made up of tissues that help them to move: bones, joints and cartilage; muscles and tendons; ligaments; nerves and nerve receptors; and blood vessels.

  • Bones are strong supporting structures, linked to each other by thick, strong, elastic tissues called ligaments.
  • Joints are places where two bones meet (for example, the shoulder joint, which allows big movements in many directions). Other joints move in fewer directions (like the knee joint, which moves in just two directions).
  • Cartilage lines the ends of the long bones, e.g. the thigh bone, and helps with smooth movement during activity. 
  • Muscles provide power to move the body via joints and to keep it upright. Muscles are very strongly fixed to the bones and around joints by tendons. There are many large and small muscles in the body that are arranged in layers, a bit like an onion.
What happens to these tissues when they are injured?

Following injury, muscles become tight to protect the body and prevent movement for a short time – perhaps hours or days. This helps the body’s healing process.

In chronic pain, when the pain does not reduce, then muscles may stay very tense. The person may be fearful of the pain and avoid being active and stretching. Gradually, over several days and weeks, the muscles, together with the ligaments and tendons, become short and stiff and feel very tight.

The vicious circle shown overleaf may help to explain why people often say, for instance, ‘the pain started in my lower arm and has now gone into other areas’.

Frequently asked questions

Q. Is it possible to loosen stiff, tight, painful muscles and joints?

A. It is possible to loosen many joints in the body, and lengthen and strengthen muscles, through gradual exercises and stretches. Learning relaxation skills helps the muscles to ‘let go’ again and become supple and flexible.

Q. If chronic pain cannot be relieved, then what?

A. It is possible to make day-to-day life more manageable despite the pain. In following articles, you will learn skills that will enable you to:

  • Feel less frustrated, worried and depressed
  • Be more physically active
  • Use medicines in helpful ways
  • Have more of a social life with family and friends
  • Become more independent in everyday activities
  • Manage setbacks confidently
  • Become better at planning, pacing and prioritizing activities

Q. Why is it difficult for doctors to understand my pain problem?

A. It is difficult for anyone to truly understand your pain experience. It can seem invisible. For doctors and physiotherapists, it is more difficult because they are unable to see, feel, hear, smell, touch or measure the pain itself using an instrument, a scan or an x-ray. For example, they can measure blood pressure or blood sugar levels but cannot measure or scan pain itself.

Q. Why don’t people take my pain seriously?

A. It can sometimes feel as if your pain is not being taken seriously. Most health professionals will believe that it is very distressing and disabling for you. Family, friends and health professionals will often be frustrated at not being able to change things for you. You could perhaps check whether they understand about the different pain systems. If not, you can use the information in this chapter. It may help them understand more about pain systems, the difficulties caused by chronic pain, how they affect you and ways to manage pain. You could also write down a list of questions to ask your doctor or physiotherapist about the pain and your body’s pain systems.

Article summary

  • Chronic pain is a different pain system in the body from acute pain. This helps to explain why pain symptoms can continue for many months or years and be difficult to relieve.
  • There is no clear link between the level or amount of pain experienced and tissue damage or injury. 
  • The Gate Control Theory of Pain helps to explain what factors can change the pain experience. Identifying what helps close your own ‘gates’ on pain messages can help you manage pain better. The euro-matrix theory begins to unravel some of the problems in the pain systems, which are complex but emphasize being in control of pain by using specific skills.
  • Muscles, joints and ligaments can lose their flexibility and become stiff and tight. These factors also help to explain why pain can sometimes persist.