The Central Nervous System

One of the most important things to understand about your body is that it is largely governed by the central nervous system (the “CNS”.)  The CNS is composed of your brain, the spinal cord and the nerves.  It is a lightning fast communication system that controls every aspect of your sensation and movement. The CNS is like the software for your body, and it determines how your hardware (the muscles, bones and joints) performs. The CNS gets to decide what muscles fire, how strong and fast they are, how far they will elongate, what motor patterns and postures you adopt, and whether you will experience pain – in short, everything that matters.

Another important thing to understand is that the priorities of the CNS are not necessarily yours.  The main priority of the CNS is to keep you alive at all costs.  While you might want to run a marathon, climb a mountain, play soccer all weekend, or sit at your computer for eight hours a day without pain, your CNS doesn’t really care about any of that – it just wants to protect you from physical threats and ensure your survival until you procreate.  Further, the CNS’s “beliefs” about what is a danger to survival are not always accurate – they are based on millions of years of evolution in an environment in which one of the main dangers was getting eaten by predators such as saber toothed tigers.  In this environment, a seemingly minor injury such as an ankle sprain or even a pulled groin is a very real threat to continued existence, and the CNS therefore takes it very seriously.  As such, your body is hardwired with a massive overabundance of reflexive and unconscious mechanisms to protect your body from physical damage.

These mechanisms will be activated reflexively and unconsciously whenever you are doing something that the CNS (not you) believes may be dangerous. Two of the most obvious protective mechanisms are pain and the startle reflex, and some less obvious ones are weakness, stiffness, and altered motor programs (e.g. limping.)  These mechanisms act like a parking brake, (or maybe an overprotective mother) in that they keep you safe but prevent you from going anywhere.

From this perspective, the fastest and most powerful way to reduce pain and increase performance is simply lowering your body’s protective mechanisms in regard to movement and posture. So lets talk about each protective mechanism in turn and how a movement training system like Z-Health can help reduce them


The startle reflex is a very primal survival mechanism that is hardwired into the nervous system of all animals.  Its purpose is to protect and guard against injury from an immediate physical threat.  The startle reflex in a human causes involuntary muscular contractions that: move the head forward and down; tense the face and jaw; bring the shoulders up and forward; and tighten the ribs and stomach.  These actions basically make us small and protect our vital areas – the face, neck, head and internal organs.

The startle reflex is flagrantly obvious when a large physical threat comes our way (see picture) but it is also present to a subtle degree when the CNS senses even minor forms of physical danger.  Thus, your muscles will tense into a startled pattern when you are doing anything that your CNS is not totally comfortable with – like lifting a heavy weight, running with less than perfect form, playing contact sports, doing a hard yoga pose, or sitting at a computer for a long time.

To complicate things further, the nervous system does not distinguish very well between physical threats and emotional threats such as traffic, a fight with your spouse, or an angry boss. As a result, emotional stress causes us to assume a physically guarded position – forward head, slumped shoulders, tight muscles in the face and abdomen.

So, although the startle reflex is designed to protect us, its awkward muscular contractions make it impossible to run well, hit a baseball, have good posture, sit at a computer comfortably, or talk to an attractive stranger at a bar.  It is therefore a wise thing to become aware of the movements (or other stimuli) that send us into the startle reflex, and start reassuring the CNS that we can perform these movements safely.  Z-Health is set up to identify movements that the body finds threatening and gently work to reduce those threats.  For example, if you can’t hold perfect posture and a relaxed face while doing a shoulder circle, your CNS is obviously threatened by this motion and you need to slow it down and reduce the range of motion until the CNS becomes comfortable with it.  Once this occurs, there is one less movement in your life that will activate the reflex and reduce your performance level.


Most people consider strength to be solely a function of how big the muscle is.  Size counts, but the more important factor is usually how many fibers the CNS allows the muscle to fire at one time.  Most people cannot get their nervous system to fire more than 30% of available muscle fibers in a particular muscle at one time.  Why?  Mostly because strength is dangerous to the integrity of the joints and the CNS knows it.  If all the fibers fired at once, the contraction would be so strong that it would be dangerous to the joints.  This sometimes occurs when someone is struck by lightning, and the incredible strength of the resulting muscular contraction can actually break bones. The CNS knows that great strength is dangerous to tendons, joints and ligaments, and only to be deployed when necessary.  In this sense, weakness can be seen as a protective mechanism of the CNS, in that it protects the body from applying sufficient force to cause injury.

One easy way to convince the CNS to allow more strength is to show it that the movement in question is safe.  For example, if your shoulder is in pain, uncoordinated, and poorly stabilized by its surrounding muscles, it is likely to buckle and experience injury if you try to press a heavy weight overhead.  The CNS knows this and simply will not allow the strength to perform the dangerous movement.  If on the other hand the shoulder is very stable, coordinated and pain free, the CNS will be “convinced” that it can handle the force, and will allow the contraction necessary to accomplish it.  So you can increase strength by coordinating the joints, reducing pain, and reducing the overall threat level related to movement.


Just like strength, most people consider flexibility to be solely a function of the physical tissues, in the way that rubber is more flexible than leather or that one rope is longer than another.  Although the physical tissues themselves are important, the CNS still plays a large role in deciding how the tissues are allowed to extend.  If it feels that the muscle has gone too far, the CNS limits flexibility by causing the muscle to contract.  Why is the CNS threatened by a large range of motion?  Because the CNS knows that extending a muscle too far can cause damage to ligaments, tendons, nerves, or even a joint dislocation.  In this sense, stiffness is a protective mechanism of the CNS.  When we are under anesthesia, and this mechanism is turned off, flexibility increases dramatically.  In fact, surgeons need to be careful when moving a patient under anesthesia because joints may be dislocated.  When we are awake, the CNS is alert to stiffen muscles whenever the body is in pain or when movement seems unsafe, or uncontrolled.  This might happen in a very local focused way – e.g. a painful ankle causes a stiff calf, or a more general global way – e.g. a painful low back and uncoordinated hips cause stiffness in the entire midsection.

You will notice when doing a stretch that if you move quickly, haphazardly or without warning, the muscle will quickly stiffen.  On the other hand, if you move into the stretch in a smooth, nonthreatening and controlled manner, you will go further in your stretches.  The simple reason is that the CNS is allowing you to do so because it knows you are under control.

Z-Health or other gentle movement systems like feldenkrais or tai chi are excellent ways to gently encourage the joints to move safely through their full range of motion.  Also, because these systems will cause a global and general lowering of the pain and threat level associated with movement, there will be a corresponding general lowering of stiffness throughout the body, even in areas that have not been specifically targeted.


Most people believe that pain is determined solely by the state of our physical tissues – if we have pain, then there must be something wrong with the tissues. Recent advances in pain science show conclusively that this is simply not true.  Although the condition of the tissues is obviously important, pain is in the brain, not the body. The brain has a great amount of discretion in “deciding” when to cause pain, and we can change the brain’s decisions in this respect.  Pain occurs when the brain “decides” that the physical tissues are in danger and that something needs to be done about it.

For example, it is very common for a man in the middle of a battle to experience no pain even after losing a limb in an explosion.  The reason is that the CNS simply decides that pain is not a useful thing at this time – getting out of the emergency situation is more important.  It is also very common for people to be pain free even when they have bulging or herniated discs in their back.  According to a famous study, in a random group of people with no back pain, 52% had bulging discs and 28% had herniated discs.  Many coroners performing dissections discover severely impinged nerves or joints that are “bone on bone” in people who did not experience pain at that joint during their life.  In other words, a great many people are able to live pain free lives even despite objective physical issues in their back or elsewhere that would cause many doctors to (perhaps foolishly) recommend surgery. On the other hand, people can experience massive pain even when there is no tissue damage at all.  The same man who felt nothing when his arm was blown off might later in life experience constant “phantom limb” pain in the missing arm.  The reason is that although the real arm is gone, the virtual arm remains in the brain, and this confuses the brain into thinking that the arm is in danger and in need of a pain signal to protect it.  Amazingly, phantom limb pain can often be cured by placing the opposite limb in a mirror box in such a way that it appears to be the phantom limb.  This fools the eyes and brain into thinking that that the phantom limb is healthy and whole, which reduces the pain.  Another example of pain without tissue damage is the condition called allodynia, which can cause massive pain even upon mere stroking of the skin.  Although the stroking does not cause any damage, the CNS misinterprets the normal sensory signals from the tissues as threatening pain signals.

To sum up, one can have significant tissue damage such as a herniated disc or arthritis without pain.  Or one could have excruciating pain with absolutely no tissue damage when the brain makes a mistake about the condition of the tissues.  The take home message is clear – if you want to reduce your pain, your target for change must include the brain, not just the body. Many prominent physical therapists on the cutting edge of recent pain science believe that a significant percentage of common pain complaints do not involve significant tissue damage, but are instead caused by the CNS getting inappropriately “wound up” and defensive about very trivial physical issues.

This is very good news for chronic pain sufferers because the CNS is very plastic and capable of change. A good movement program should be directed towards changing the way the brain thinks about the body. A good way to do this is by showing the brain novel and interesting movements that are pain free.  The CNS considers the new movement option to be “good news”, and immediately lowers the overall threat level associated with that movement and similar movements.  In fact, studies show that one of the best predictors of back pain is not the objective condition of the tissues in the back but the patients’ fear of certain movements.  This is why the safe gentle movements in Z-Health can often lower pain levels dramatically and easily.


Another protective mechanism of the CNS is altered motor programs, in other words a change in the way your muscular movements are coordinated by the CNS.  One obvious example of an altered motor program is limping.  If you injure your ankle, your CNS will immediately begin working beneath your conscious awareness to protect the ankle when walking.  It does this by using nearly all of the other muscles and joints in the body in a slightly different way to walk without hurting the ankle.  The same things goes for any other pain in your body, even small subtle pains - the CNS will immediately start working around the pain by changing movement patterns in subtle or obvious ways.  This is a good idea in the short term – it protects the injured area and gives it a chance to heal. But in the long term, the altered movement programs can persist as habits even after they are useful. This means that anyone who has experienced an injury, even years ago – may be subtly guarding the injury even now as a result of persisting altered compensatory patters.

In fact, nearly all of your basic motor patterns such as the lunge, squat, reach and twist, are likely “infected” with subtle little compensations that are below your conscious awareness.  Trying to perfect these movements on their own will likely not correct but only reinforce the altered pattern because the compensations are below conscious awareness.  In order to identify and correct the little movements that you have started avoiding unconsciously, you may need to isolate these movements joint by joint in a very precise and systematic manner.  This will restore the movements that have been lost, and encourage your CNS to change old habits that are no longer useful.