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Explaining pain

Patient information A-Z

What is pain?

Pain has been defined as: “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” (International Association for the Study of Pain, 1979).

How do we respond to pain?

The important bit to note here is ‘potential’ tissue damage. Actual tissue damage does not have to occur for pain signals to be made.

Stimulus / response model

In a simple injury such as a cut, the initial injury causes nerves to send lots of impulses to the brain to tell it that tissue has been damaged. As the healing process starts, other nerves are activated to protect the vulnerable area by making it more sensitive. As the tissue heals and gets stronger the pain signal should slowly fade. However, in some cases this does not happen.

The ‘pain gate’ model

This theory suggests there is a ‘gate’ in the spinal cord, which can be opened or closed to varying degrees. This 'gate' is designed to be able to increase or decrease the pain you feel following an injury.

Opening the gate

  • Fear
  • Anxiety
  • Depression
  • Poor sleep
  • Overdoing it
  • Stress

Closing the gate

  • Happiness
  • Excitement
  • Interest
  • Pacing
  • Exercise
  • Relaxation

So what goes wrong in chronic pain?

In most people, once the initial injury has healed, the pain signal starts to fade. It eventually goes away completely. In some people, however, the pain signal does not decrease, even after the injury is fully healed. In these cases, the nervous system has ‘learnt’ the pain. The signal effectively becomes stuck and the gate is left open. The pain signal is no longer a useful signal to prevent injury or to encourage us to protect an area as it heals. In addition, the ‘open gate’ may mean that even normally pain free sensations such as a stretch may be painful. This means that injury is not the problem. The problem is the pain. This is often made worse as people will try to protect painful joints and muscles by not using them. This leads to weakness and tightness, which can further lower the pain thresholds.

The ‘constantly learning’ nervous system

This theory recognises the nervous system is constantly learning and adapting to events. Your background, beliefs, past experiences (good and bad), physical health, relationships and work happiness can all affect the way you experience your pain. A chronic pain problem can have a devastating affect on all areas of a person's life. In effect, many people find that their pain becomes their main focus. They become trapped in a pain ‘bubble’.

Managing your pain

Sometimes we are not trying to ‘cure’ the pain but hopefully to burst the bubble and put the pain back in its place. As a result of managing the pain better, improving your fitness and regaining control of your life, you will find that your pain levels can improve. More importantly it will have less impact on your life.

Pain relief

To help us optimise your treatment it is important that you have adequate pain relief. If you are suffering high levels of pain please seek advice from your pharmacist or GP.

Further advice

Please be aware that this handout is to be used as a guide.


Please contact our reception on 01223 216633 to leave a message for your physiotherapist, or to enquire about appointments.

This information has been compiled by the physiotherapy team at Addenbrooke’s hospital. You may receive this information during an appointment with a physiotherapist, from your GP or via the CUH physiotherapy webpage.

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Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151