About Pain

The Pain System #4 - Some more of the science



"Stress biology is concerned with the physiological mechanisms and behavioural strategies that enable organisms to survive or maintain homeostasis” “Pains prime adaptive purpose is to powerfully motivate the organism to alter behaviour in order to aid recovery and survive” 

(Gifford 1998)

This blog is an appendix to the previous three blogs on pain response and sensitisation. It is intended to give some more detailed background on how the brain in particular manages pain.

Part 1: How our Tissue Responds to Pain

Part 2: Amplifying Pain - Central Sensitisation

Pain 3: Shark Attack, It's all in the Mind

The basic function of pain is:

• To protect you.
• To alert you to danger - often before you are injured or badly hurt.
• To makes you move and think differently
• VITAL for healing

Pain is a normal response to what your brain judges to be a threatening situation.

The basic pain mechanism involves
Input / stimulus (the nerve endings in tissue) => process and evaluate (the spinal cord and brain) => output / response (the whole body). “We need a system that is able to monitor health of organisms own body and provide appropriate recovery response if damage occurs” (Gifford 1) Is Pain is all in your mind? Well, yes. The following areas of the brain are involved in evaluating pain inputs and formulating responses:

• area for organising and preparing movement.
• area for concentration and focus.
• area for problem solving and memory.
• fear, fear conditioning and addiction area.
• sensory discrimination area.
• area for stress response, autonomic regulation and motivation.
• movement and cognition area.

Following a potentially painful stimuli the evaluation and response also involves many different systems of the body:

1. The Sympathetic nervous system - this increases heart rate, mobilises energy stores ready for movement and releases adrenaline into the body.
2. The Motor (muscle) system is very important e.g. remove limb from flame, limp, run away, hide, prevent movement of area under threat. As we have seen, one problem is once trained the body tends to maintain these patterns after the stimulus has gone.
3. The Pain system itself - this lets you know what is going on i.e. you feel pain
4. The Endocrine system - Mobilises energy stores and suppresses any processes that are not vital to save energy (growth, repair processes, inhibition of inflammation, and inhibition of the immune system)
5. The Immune system - responds later and fights invaders, sensitises neurones, makes us sleepy to promote healing.
6. The Parasympathetic system - also responds later, it nourishes cells and heals tissue.

These systems are designed to work really hard for short periods in a threatening situation. They are the same systems that are activated when your body is under acute stress and are responsible to flight / fight responses. In the same way that prolonged stress which maintains long term activity in these systems is is undesirable, pain for a prolonged time causes sustained activity in these systems which causes over-sensitisation.

Persistent, chronic pain:

All pain is real but some pain persists after healing has occurred. This is termed persistent pain or chronic pain. In these situations the brain concludes that a threat remains and you still need protection. The brain can experience similar sensitisation to that described for the spinal chord in blog #2. The pain ignition nodes in the brain increase their sensitivity so less stimulus from the spinal cord activates them. They can even start firing with no stimulus from the spinal cord. The brain also creates more sensors in the pain ignition nodes and produces more chemicals to activate the sensors. This can be particularly powerful when it occurs in the part of the brain that deals with memory - you can relive the pain even though there is no danger to respond to. For example people with whiplash can feel pain when the car ahead stops even though they are not themselves stopping suddenly. The brain areas devoted to different body parts or functions start to overlap making you sensitised to pain in different areas of the body to where the stimulus originally occurred. This is conceptually similar to the chemical flooding of the dorsal horns in the spinal cord. The longer the pain persists the more advance these changes become. When the brain is sensitised it's not just pain that is persistently produced. Other protective systems also increase their sensitivity:

• The Sympathetic Nervous System makes you more aware and vigilant - as if you have turned a CCTV onto your body.
• The Endocrine system directs more energy to muscles for flight or fight.
• The Motor system keeps muscles constantly activated ready for fight or flight.

These systems then send signals to the brain in a self-perpetuating feedback loop. With a sensitive system inputs unrelated to tissue damage are judged as dangerous and can cause pain. You won’t know there is no damage or that its just your brain decided dangerous. It just hurts. Your thoughts are real. Real chemicals are released and real nerve impulses occur. Thought processes alone are powerful enough to maintain a pain state.


Altered muscle activity:

When you are in pain your brain alters your muscles activity. With pain being a warning sign for danger your body firstly increases activation of muscles to ready you to take action - flight or fight. This reaction is to aid protection of the whole body from further threat.

It also changes how your muscles work to help protect the local tissue where the pain is top prevent further damage. These changes cause bracing / splinting of the area by increasing the tension of muscles around the pain, and altering the movement of the whole area to reduce the load on the painful area (such as limping, or grasping the area). This works through taking load off the injured tissue by putting more load through surrounding tissue.

In the short-term these are all a positive strategy by your brain to protect your body. In the long term it becomes a hindrance not a help. 

Long term over-activation of these muscles makes them feel stiff and tight. This tightness can then change how you use other muscles. Smaller muscles who's role is to control and stabilise stop working as effectively as they perceive the larger muscles to be doing their job.

This altered muscle activity will then change how you move, feel and hold yourself.

So in rehabilitating any injury you need to address these changes in muscle activity. This is done with traditionally stretches and strengthening activities as well identifying and addressing threats and fears that are making your muscle system work so hard to protect you.


References

Gifford L, (1998) Topical Issues in Pain 1. Physiotherapy pain Association

Butler D.S, Moseley L.G (2013) Explain Pain, Noigroup Publications. 

Mense S, Gerwin R D, (2010) Muscle Pain - Understanding the mechanisms, Springer

Melzack R, Wal P.D (2008) The Challenge of Pain, Penguin Books.

Shark attack! It's all in the mind.

The Pain System #3.

"On 31 October 2003. Bethany Hamilton was surfing with her best friend, Alana Blanchard. At first, Hamilton didn’t realize what had happened. She saw a grey flash and felt a short tug. But when she looked down, the water was bright red and her left arm and a large chunk of her surfboard were missing.

“I’ve just been attacked by a shark,” she stated calmly, and started paddling towards the shore with one arm." (The Guardian, 2016) 

We've already seen in previous blogs something of how the body generates pain signals chemically and electrically in response to external stimuli.

Part 1: How our Tissue Responds to Pain
Part 2: Amplifying Pain - Central Sensitisation

But our slippery-tricksy brains have the final say in any pain experience. At the extremes they can generate pain with no external stimulus. Conversely they can ignore external stimulus that is causing the body harm so that no pain is felt at all, usually when a greater threat is present - as Bethany experienced.

For the majority of us there are many factors that cause the brain to respond in a certain way, generating more, stronger pain messages on some occasions or fewer, weaker ones on others. What is useful is that it doesn't take a rocket scientist or brain surgeon to recognise these behaviours. Most of us are reasonably self-aware. Just as we can train our bodies to be fitter for purpose we can train our brains to be better at pain interpretation.

Pain Face. Finishing The Exterminator

The brain is your body's command centre. Danger messages and pain messages arrive at the brain which then processes them alongside other messages such as "there is a lion over there." Even though the pain systems in the other parts of the body can generate signals in response to real stimulus and can become oversensitised, you won't feel pain without the brain's involvement.

The brain's challenge is to construct a sensible story based on all information arriving along with the information already stored in the brain. With any pain experience hundreds of parts of the brain are involved simultaneously.

There are some consistent patterns in this brain activity but the exact parts and amount of activity in each part varies from person to person and within each person. Each and every pain experience is unique. Particularly those of my husband.

“It's the brain that makes the final decision whether or not you should be in pain”

(Butler & Moseley)

Are you experienced?

Your past and recent experiences have a huge effect on how the brain interprets pain signals. Factors include: 

• previous injuries, 
• past experiences, both your own and of others
• your knowledge
• your beliefs
• Past successful behaviours
• Past successful behaviours in others
• and of course those unhelpful behaviours the human resources department keeps going on about.

All pain is produced by the brain. 

No brain = no pain.  

No pain = no gain.

No brain => no gain. QED. 

In an perfect Brave New World - scientific, empirical, logical, evaluated and analytical - we would build a bank of good responses to pain. Our subconscious and conscious decisions would support and reinforce recovery, prevent more damage and maintain function. 

Humans use logic to predict the future (often badly) which enables us to then plan for future events. This gives us the capacity to identify potential dangerous situations and plan appropriately. 

Everyone's an expert.

In the ‘good old days’ there was a very limited amount of outside resources to help us evaluate danger signals. The modern era has dramatically increased this influence of others in how we respond. 

The internet has brought forth an army of experts, pesudo-experts and self-styled opinion makers, some well-meaning, others purely opportunistic. Many are unhelpful. 

There is also access to a wide array of health professionals; GPs, nurses, consultants, physio's, osteopaths and chiropractors. All put their own slant on our pain stories. 

A good experience with health experts can increase your knowledge, calm your fears and give you a good plan of how to move forward. 

Alternatively each expert offers his own opinion, you receive lots of conflicting advice causing doubt, increasing uncertainty and even fear. The bedside manner of some busy health professionals leaves much to be desired and it is common for them to deliver catastrophising messages without meaning too which we then filter and reinforce 

“I need to strap my calf to stop it snapping", 

"My back is twisted"

"My spine is crumbling"

"I have chronic arthritis in my knee, therefore I can't do anything" 

"I must never run again" 

"My core is weak" 

The Cosmo Pain Management Quiz - which one are you?

Score 0 - 10:  The Ostrich:

You ignore your pain. You're an ignorer. The ultimate ignorers have no pain sensation and don't tend to live very long!  

There is a rare condition called congenital insensitivity to pain (CIP) and sufferers are unable to feel any pain. Sadly their life expectancy is significantly reduced as a result. 

Other people have a high tolerance to pain, tend to ignore it and push on. Such people are likely to ’get away with’ pushing on through many pains but they will eventually hit a pain that doesn't resolve. It's possible Alastair Brownlee has been one of these.

Push-on'ers can end up in a very confused place once the injuries build up. They can then become Yo-Yos.

Score 10 - 20: The Spooks:

Him indoors loves his spy stories, both real and fictional. A common theme is that once you start thinking like a spy setting up plays, misinformation and double-crosses then everything becomes evaluated through that distorted prism.

Spooks tend to listen too much to their pain and consequently act too much. 

"Pain is harmful therefore I must rest until it completely goes". 

"I’m not running again until I am pain free." 

In the mind of the spook pain means "damaged", no pain means "healed".

"It hurts a lot so I will tape it to stop it breaking." 

"I can’t do X/Y/Z because it hurts and I will break."

Score 30 - 500: The Yo-Yos:

Yo-Yo oscillate between the Ostriches and the Spooks. They do too much, often too quickly, which leads to pain and possibly injury. In response they STOP. Everything.

But stopping training reduces the body's tolerance to load and general robustness. But they've stopped so the pain goes. Then they start again, perhaps tentatively but they very quickly return to the loading levels they were putting the body through that caused the injury with obvious consequences.

With each cycle the body becomes more sensitised, less tolerant and more fearful of pain in a feedback loop that increases the magnitude of the Yo-Yo.

At Kim Baxter Physiotherapy we see many Yo-Yos. I regularly treat runners who have been Yo-Yoing for long periods and for whom it has been many years since they have put together sustained periods of injury-free training.

The key to successful management for Yo-Yos is to break the cycle. This is done by starting with a base load the body can tolerate and systematically building up the load and training. This is easier said than done. 

Understanding pain helps reduce your fear

Fear has a huge effect on your pain experience. Anything that increases the brain's perception of the need to protect can increase pain.

Here are some common fear factors related to pain:

• Fear of the seriousness of the cause of pain - is it cancer, is it very damaged etc
• Fear of the unknown - not knowing what it is
• Fear of not being believed, not being listened to
• Fear of certain movements / activities
• Fear of re-injury
• Fear of delaying / preventing injury
• Fear that it hasn’t healed
• Fear of doing more damage
• Fear of not being able to work, train, garden, look after kids etc
• Fear of not being able to do race or having to pull out of race
• Fear of injury reducing performance
• Fear of the garden turning into a jungle or the house becoming a bombsite
• Fear of pain meaning you're getting old
• Fear that your joints are wearing out
• Fear that this is it - its never going to get better than this and will only get worse
• Fear of having a nervous breakdown 
• Fear of gaining weight
• Fear of what other's think
• Fear of possibly having to have surgery
• Fear of the treatment - it might hurt, don't like needles, anaesthetic
• Fear the medical professionals won't be able to help
• Fear I am doomed

Fear affects your mood. Your mood affects your pain. Yet another feedback loop.

Fear makes your pain worse

A study of patients post breast-surgery found that those who attribute pain to returning cancer experience more intense and unpleasant pain than those who attribute it to other causes regardless of what is actually happening to the tissue. 

The reporting of pain is also affected by social factors: studies show males have a higher pain threshold if tested by females whilst patients with an attentive caring spouse has a lower pain threshold than patients with uncaring spouses. This of course explains why my husband is so pain sensitive.

We need to train our brains to really understand pain, what it is and what it is not. This is especially important when pain persists, spreads or seems unpredictable. 

So what does this mean for you? 

It is important to understand pain and how it works. The more understanding you have of pain the better you can manage pain events. This is the art of listening when you need to and ignoring at other times. 

Understanding and practice can help you make sense of new pain events and break old patterns of behaviour. 

Hurt does not equal harm. But hurt does need to be listened to and evaluated. 

And, as everyone is individual i.e. different, this must necessarily be empirical but it can still be logical and scientific. You need to objectively evaluate what works for you and what doesn't.

Butler D.S, Moseley L.G (2013) Explain Pain, Noigroup Publications. 

Mense S, Gerwin R D, (2010) Muscle Pain - Understanding the mechanisms, Springer
Melzack R, Wal P.D (2008) The Challenge of Pain, Penguin Books.

Amplifying pain: Central Sensitisation

Anyone remember William of Ockham? (Thanks Wikipedia). Occam’s razor? The simplest explanation is usually the best?

Well, it’s rarely like that when explaining the body. It turns out the pain system has a middle bit. A bit between the nerve endings and the brain. Who knew? And why? Why make it so complicated?

In this article we concentrate on this middle bit of the pain system, the spinal cord. It starts at the coccyx and travels all the way up your back to your brain.

The peripheral nerves, discussed in the last blog, provide the inputs to the system. They can be thought of as alarm bells. They feed messages to the spinal cord from all parts of the body: skin, tendon, muscle, bone, organs and even nerve tissue itself. 

These messages are simply danger signals. It is then the job of the spinal cord (the preprocessor), and the brain (the main command centre) to analyse them and create a meaningful experience/response. This experience may or may not include pain.

The messages from the peripheral nerves are quite basic e.g. the temperature in the tissue has increased, the acid level has decreased, there is more pressure etc.The complex sensations that we feel in response such as strong pain, tearing, stretching, throbbing, aching, crawling etc are all created by the brain. 

What occurs in our tissues is only one part of the pain experience. The messages from the tissue require evaluation by the rest of nervous system. The spinal cord is the first part of this evaluation process and it determines what messages are transferred from the peripheral nerves up to the brain. 

The spinal cord is a network of nerves with vertical lines up to the brain and back down from the brain along with collateral lines connecting the vertical lines. There are many junctions or synapses where peripheral nerves connect.

The spinal cord acts as a preprocessor, "sorting" the incoming signals. It can both block and amplify messages. 

Blocking: 

One of the nerves back down from the brain is able to flood the junction of the peripheral nerve and the spinal cord with chemicals that block any messages travelling up. It does this when the brain perceives that the whole body is in imminent danger of some external threat and it needs to act to escape the threat. 

Blocking pain in this way enables someone with a broken leg to run away from a lion or to complete a 400m relay race in the Olympics - as Manteo Mitchell did for the U.S. Team in the 2012 Olympics qualifying race.

Amplifying (Central Sensitisation): 

The peripheral nerves from different parts of the body have their junction with the spinal cord at different levels of the back. The foot connects at the very bottom of the back whereas the hand connects at the bottom of the neck. On one side of the body there are thirty one entry points called dorsal horns that run down the spine from the neck to the lower back. 

A message from the peripheral nerve causes the end of the nerve to release chemicals into the gap or junction at the dorsal horn. These chemicals attach to the end of the nerve coming down from the brain causing a message to fire up to the brain.

When we get a long lasting or strong input from a peripheral nerve to the spinal cord and up to the lower brain (the brain stem) the neurons (the cells of the nervous system) change their reaction to the input. They become more sensitive and send up a greater reaction than the input represents.

Such changes do not take long to develop. 

A few minutes of strong input from a peripheral nerve is sufficient to change the sensitivity. 

This “central sensitisation” is similar to an unwanted learning process. Once it has occurred the pain experienced can become more intense and continuous than the stress or load in the tissue warrants. In this state messages from the junction can be fired up the spinal cord to the brain even when there has been no input from the peripheral nerves. 

These changes in firing patterns occur not only at the level that the initial strong input was experienced, but also to adjacent junctions above, below and on the opposite side of the spine.

Current research is investigating theories that phantom pains which manifest in areas of the body disconnected from the original injury can be caused by chemicals flooding the gaps between the dorsal horns. Whilst an oversimplification it perhaps helps understand what might be happening.

The theory is that whilst a referred pain may be bio-mechanical it may also be, in effect, chemical i.e. caused purely by the pain system’s chemical transmission of the original stimulus, not by a bio-mechanical consequence of the original stimulus. 

What happens when central sensitisation develops?

The result of this increased sensitivity is that the brain is being fed messages which do not represent the true state and abilities of the tissue, so that an area that hurts a little can hurt a lot, and an area that didn’t hurt at all can start hurting.

Once sensitisation has occurred preventing the pain becomes more difficult.It may not simply be a case of removing the stimulus that caused the initial nerve signal or allowing the tissue to heal. 

You also have to unlearn the pain response.

A patient who has suffered a sudden short-lived pain that is relatively mild is unlikely to have central sensitisation. Treatment can often produce a dramatic resolution of symptoms and the patient can sometimes feel immediately better.

However if central sensitisation has occurred this sudden turnaround rarely happens and in some cases hands-on treatment can make the patient feel worse as it further stimulates the irritated nerves. 

Changing this learned behaviour requires a gradual calming down of the system, which takes time.

What are the indicators of a sensitised nervous system? 

In the clinic I start to suspect that sensitisation is part of the picture when:

• Pain continues after the expected healing time
• Pain starts in a very local spot where the ‘injury’ first occurs then spreads and moves around the tissue.
• The pain becomes ‘illogical’ in that it doesn't fit the pattern of how much stress or load has been put on the tissue. It becomes less predictable.
• Random stabs and twinges are experienced for no apparent reason
• Random pains occur in other tissue e.g. a hamstring starts to hurt when it is the calf that has been injured. 
• The pain is mirrored on the other side of the body. 

Case study - no central sensitisation 

The physical input e.g. load, damage is proportional to the physical output e.g. pain, swelling, etc.

Note this is an idealised scenario comprising an amalgamation of the experiences of several patients.

Active fellrunner Mr T arrived at the clinic with achilles pain. He had just done his first parkrun. When asked where the pain was he pointed with one finger to an exact spot on his achilles. 

His achilles tendon wasn’t used to the different loading patterns of running flat out on tarmac for a relatively short period of time. 

The pain worsened with any faster running and uphill running, but did not occur with activities such as walking and long slow runs, which place less load on the achilles.

There was a consistent pattern to the manifestation of the pain - it was very localised and increased and decreased with increasing and decreasing load. 

After tuning his training load and adding extra strengthening work he returned to normal training but understood that he needed to build up to races that would place his achilles and other tissues under different loads.

Case study - with central sensitisation

Mr P booked in for physio 3 weeks after he sprained his ankle. The pain he was experiencing seemed commensurate with the severity of his initial injury, a quite nasty sprain right at the start of a fell race which was very swollen for several days with significant bruising. 

Three weeks on he had regained full movement and reasonable balance and could hop with only mild ache. He was set for moving forward with rehabilitation to get back to running and racing.

However Mr P was concerned. The ankle was still painful. He could feel it throughout the day even with walking and especially worrying was that the light pressure of his trouser leg or the duvet caused pain. Due to this pain he was trying to protect the ankle and avoid anything that could harm it further. 

Assessment of strength, movement and function combined with knowledge and experience of typical healing times lead me to feel confident the ankle was mending well.

So why the pain? This was a classic example of a type of central sensitisation called allodynia - “Mechanical allodynia (other pain) is a painful sensation caused by innocuous stimuli like light touch (Lolinger et al 2015).”

Once this was explained to Mr P his concerns regards damage and harm were alleviated and the process of building up strength to return running could begin. 

References:

Lolignier S, Eijkelkamp N, Wood JN (2015) Mechanical Allodynia, Pflugers Archive

Butler D.S, Moseley L.G (2013) Explain Pain, Noigroup Publications. 

Mense S, Gerwin R D, (2010) Muscle Pain - Understanding the mechanisms, Springer