Pain is unpleasant, but it’s also useful. It tells us that there’s a problem. It prompts us to get out of a dangerous situation. When the danger passes, so should the pain – but sometimes it doesn’t. In some cases it can linger for years. So what do we understand about pain and why it sticks around?

We look at what’s happening when you experience pain, examine the latest theories about how chronic pain develops, and consider the best ways to tackle it.

Acute and chronic pain

One common way of categorising pain relates to how long it persists.

Acute pain lasts for up to three months, whereas pain lasting longer is deemed to be chronic.

Why this time limit? Because most tissue damage, such as a strained muscle or broken bone, heals in three months, so we might expect the pain to stop at the same time.

Pain can persist because of an ongoing condition, such as arthritis. However, sometimes it happens because the nervous system continues to think there’s a threat, even after all the danger has passed.

To understand chronic pain, we need to look at how pain works.

Understanding the pain mechanism

In its simplest form, pain occurs when certain receptors send a signal via the spinal cord to the brain. If the brain decides the signal is sufficiently important, you experience pain, which encourages you to take action to protect yourself.

The critical step is how the brain makes that decision. It considers a lot of factors, including visual stimuli, context and memories, to work out whether there’s a risk.

In fact, researchers have been able to alter the amount of pain people experience by changing some of these factors.

In one study, researchers applied cold metal to people’s arms whilst showing them a blue light or a red one.

Although there was no difference in the stimulus, people who saw the red light reported severe, burning pain. Our association of red with heat changes how our brain interprets the signal.

And, along with visual signals, our experiences, memories and beliefs have a similar impact.

The placebo effect, in which people feel benefit from a ‘dummy’ treatment if they believe it works, demonstrates this. It’s the expectation of success that persuades the brain to experience less pain and symptoms.

Therefore, we know the things we believe and understand about pain are important in determining the extent to which we experience it.

In this way, we can see that pain is complex. It’s not a simple response to nerve inputs, but a multi-factorial decision process, based on our experiences and our interpretation of the circumstances.

The vicious cycle of chronic pain

According to the Chartered Society of Physiotherapists, between 20% and 50% of people in the UK experience chronic pain. But why is it so common?

It seems that pain can affect the central nervous system’s processing and become a self-perpetuating cycle.

Pain researchers have found that chronic pain can alter the brain’s representation of a painful body part.

One researcher, investigating pain in osteoarthritis, found that patients perceive the size of their arthritic joints as smaller than they are in reality, and that artificially changing that perception can reduce, or even stop, their pain.

Similarly, other studies have shown that people with chronic pain have a faulty sense of their body movement. When the brain initiates a movement, it monitors the progress of that movement through visual and sensory feedback.

But research shows that, in people with chronic pain, there’s an incongruence between what the brain expects and what it senses is happening. Researchers think this discrepancy may trigger pain – a bit like the way disjointed visual and balance sensations can lead to motion sickness.

In addition to these sensory errors, ongoing pain can change neural pathways in a way that makes us more likely to feel pain.

Nerves in the spinal cord have a threshold of firing – a point below which they won’t relay an incoming signal. However, if they are continuously being triggered, such as during pain, that threshold can lower.

This means a smaller incoming signal will set these nerves off. In effect, the nervous system becomes more sensitive to pain, and more likely to feel it.

In fact, this sensitisation means warning signals are still sent to the brain even when injuries have completely healed. An injury can leave a legacy of pain in the nervous system in the same way it can leave a scar on the skin.

As we begin to understand how chronic pain occurs, we can develop new ways to treat it.

Treatment for chronic pain

Increasing our understanding of chronic pain increases the possibilities for treatment.

We know chronic pain can occur solely within the nervous system, separate from any damage in the body. But people associate pain with damage, and so may avoid normal activity. Reduced function leads, in turn, to greater pain and more fear. This cycle of pain-fear-pain needs to be broken.

Retraining the nervous system using a graded programme can re-establish normal movement, reducing pain and improving function.

One study looked at pain intensity in 138 patients with chronic low back pain. They underwent an 18-week, three-step treatment programme. The first step involved education, to help the patients understand their pain. The second used mental rehearsing and movement precision training. This step improves the brain’s perception of body movements and develops confidence. Finally, patients progressed from simple movements to complex ones, such as squats, lunges and lifting.

This progressive, confidence-building plan enabled patients with chronic pain to regain function, while their pain was significantly lessened.

Other research, on physiotherapy interventions for chronic pain, had a similar focus on education and sensorimotor training of patients, for whom previous treatments hadn’t worked. The treatment improved scores for pain, function and overall health.

And osteopathy, too, is effective at treating chronic low back pain. One clinical trial looked at the effect of six osteopathic sessions, given to 230 patients over eight weeks. It found significant improvements in both pain and function, compared to patients treated with ‘sham’ osteopathy.

Physiotherapists and osteopaths understand chronic pain, how it develops and how it can affect your life. They are ideally placed to create a treatment plan, working with you to achieve your goals – whether that’s a return to competitive sport, or simply living life in greater comfort.