General Adaptation Syndrome

General Adaptation Syndrome

An article by Daniel Hunt

Once upon a time, in a sandy kingdom far, far away - the physicians of ancient Egypt believed that the heart was the centre of all bodily function (REF 1), and that other important organs functioned simply to support the heart. This included intelligence, thought, emotions, and even digestive function. It is fairly common knowledge in today’s age that our emotional responses to external events are caused by chemicals released within the body. In terms of our response to stress specifically - that hormone responsible is called cortisol (REF 2). Often referred to as the ‘stress hormone’, cortisol is released by the adrenal glands in response to perceived threats from our external environment. Cortisol is the body’s alarm system, and as soon as our brain identifies a possible threat - the message is sent through the nervous system to begin the appropriate response. What qualifies as a ‘threat’ is fairly flexible, since we all feel stress for many different reasons - and the word ‘threat’ likely makes you think of something deadly. Whilst life threatening stimulation was probably more common in ancient Egypt, the modern era (at least in the Western world) is more concerned with ‘first-world problems’. We individually respond to what our bodies perceive as ‘stressful’ - whether this is a physically demanding situation, or an ongoing experience of psychological stress. Importantly, the threats that trigger our stress response can be actual or perceived - it is entirely up to how your brain interprets the external environment. What’s consistent about all of these; past, present and future - is that they elicit a stress response. 

Stress responses, like all hormone driven reactions, cause physical changes to happen to the body. Heart rate, breathing, blood pressure, and other easily observable indicators increase or change in response to the release of cortisol - these physical changes, along with the less obvious (but equally as important) internal ones - are done in the name of survival. By making these physical changes, your body can respond to and tolerate external stressors more effectively - whether that’s fighting off an attacker or fleeing from a threat.

GAS & Sympathetic Nervous System

In my last article (REF 3), I laid out the basic foundations of the human nervous system - including the major players and the lesser known ones. Whilst I did briefly touch on it in that article, the focus point for this discussion will be the Sympathetic Nervous System (SNS) - more accurately, General Adaptation Syndrome (GAS). While you may not have heard of GAS, you’ve likely heard of ‘fight or flight’ - or ‘fight, flight or freeze’, as it is becoming known. Fight, flight or freeze are the instinctive human reactions to immediate threats - a primal response fueled by survival instinct. Were this response to be triggered, you would have the following automatic reaction - much like a reflex, the body has evolved to make these kinds of survival instincts as fast as possible to improve chances of survival. It is worth noting that your individual reaction can be influenced by training and re-conditioning, much like what is done in the military to combat soldiers - through repetition, a person’s instinctive reaction can become a practiced pattern. Hence the saying, “You won’t rise to the occasion, you’ll fall back to your level of training”. This may not sound very heroic, but it is more often than not the reality. However, the vast majority of the population has not been re-conditioned through military training - and fight, flight or freeze are more relevant.

GAS breaks down these primal reactions into three phases - alarm, resistance, and exhaustion. These phases begin at initial exposure to a perceived threat, and span over an extended period of stress - detailing the bodies coping strategies for longer term exposure. Essentially, as time progresses, the body can only keep up with high levels of stress for a limited amount of time - that timeframe differs from person to person due to many individual variables. Like any other biological or mechanical system, working at excessive operating levels will cause ‘burn out’ - reducing the efficiency and capability of that system. For the human body, this means organ systems begin to shut down, and experience greatly reduced cognitive ability - with long enough periods of high stress and low energy-intake potentially contributing to death. That’s the very extremes, and while not everyone reaches the final phase of GAS - some certainly do. Examples of this exhaustion would include working long hours and having subpar sleep for a long period (several weeks or months), where you begin to feel ‘run down’ - commonly followed by a flu, as the body's immune system cannot maintain enough energy to effectively fight off sickness. High demand on our time and sacrificing sleep are common in the Western world, so it’s an easy example to make. 

I’ll now touch on each phase of General Adaptation Syndrome, and as I do so - you may be able to identify times where you have reached particular phases.

Alarm Phase

The first phase of GAS is where your instinctive responses are triggered, and activated by perceived threats. Again, examples vary in extremity, yet everyone has experienced this - despite how tough someone might think they are. Whether you’ve jumped at a scary movie, pushed away an aggressor, or frozen like a deer in headlights - the human body has adapted very well in the name of avoiding possible damage. Even the freeze response serves a function to deter threat. Internally, physical changes taking place include an increased heart rate, blood pressure, and release of cortisol and adrenaline from the adrenal glands (REF 4). The body undergoes a kind of ‘prioritisation of bodily functions’, where things like reproductive and digestive organs inhibit their functions to allow more blood flow to the heart, muscles and brain. To support the body in doing so, energy stores get used in larger quantities to fuel the possible fight or flight.

Resistance Phase

Once the initial shock of a perceived threat subsides, and the fight, flight or freeze reaction is completed - the body begins to return to its pre-stress state. The amount of cortisol being produced decreases, and heart rate and blood pressure begin to normalise. Assuming the stressor is removed, your body returns to what is called ‘homeostasis’ - simply put, that’s just your own ‘normal levels’. If the stressor is not removed, then the body will still attempt to normalise the aforementioned levels - however, it remains on high alert. By remaining in this level of hypervigilance, stress hormone continues to be released and your blood pressure remains elevated. Without you realising it, your body attempts to cope with the elevated stress by adapting - and if you feel your ability to cope with high stress levels is productive, these adjusted physical changes can lead to the third and final phase of GAS.

Common signs that you may be experiencing this phase include irritability or frustration, and poor levels of concentration - indicators for reduced cognitive ability.

Exhaustion Phase

The resistance phase can last weeks or months, but once the stress has become prolonged or chronic enough - your body reaches exhaustion. In this phase, you’re rapidly reducing your body’s resistance to ongoing stressors - with the signs and symptoms you experience becoming more severe and damaging. Mentally, someone experiencing stress exhaustion may display increased levels of cognitive decline, along with depression and anxiety-like symptoms. Physically, your body simply doesn’t have the energy to function at its most effective level - causing fatigue and reduced capability in organ systems, such as the poor immune response example I mentioned earlier. Extreme examples of the negative effects of exhaustion can include death or chronic illness, however in the Western world - stress is more likely going to be a contributor to chronic illness as opposed to the sole reason.

Rest Is For The Strong

You may have seen the phrase “Rest is for the weak” or “I’ll sleep when I’m dead” on a T-Shirt or some motivational social media post - however, they more than likely exist to validate poor lifestyle choices than anything else. Resistance to stress is influenced by age, health, and other general lifestyle choices - what this doesn’t change is that everyone will experience stress during the course of their life regardless of their resistance ability. To effectively deal with this, there needs to be coping strategies in place which can assist you in ‘easing off the accelerator’. By this I mean taking some time to slow yourself down mentally and physically, for the sake of recovery. The way you achieve this is fairly dependent on what you personally find beneficial, and the context - you may just need to dedicate more time to sleep each night, or you could find breathing techniques helpful when immediate tasks are causing stress during the work day. It’s also necessary to differentiate between what is ‘fun’ and what is actually recovery - as social drinking may be fun and relaxing, but not very conducive to recovering from a physically intense week. Exercise, breathing techniques, even meditation - are all viable strategies for dealing with stress, and should be utilised consistently for the sake of maintenance. These strategies must be sustainable - and like any other skill, are built with time and practice. If you are struggling to find strategies that are most supportive for you - reaching out to a health professional can be beneficial.


The human body responds to stress in the best way it can, adapting to stressors over thousands of years to best serve our survival instinct. The benefit of the GAS response is that it does improve your ability to respond and resist stress, primarily during the alarm phase - hence the ‘adaptation’. Short-term stress is normal and generally won’t cause damage, but as I’ve discussed above, prolonged periods will cause negative effects which should be taken seriously - with the use of coping strategies and recovery. Choose your own adventure when it comes to finding an effective coping and recovery method, because methods that may suit myself or others may not be most supportive for you as an individual. Keep the strategies sustainable, as there can be a fine line between ‘letting off some steam’ and outright counterproductive choices. If you have further questions or are just generally curious, I recommend looking at the references I’ve included below - or taking the time to research some for yourself. The human body is very interesting to read about, especially if you can find a source which limits the amount of complex science words so that us normal people can understand it.


Train Smart. Train Hard.






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Anvil Training and Development is a group of Australian veterans who care about the physical and mental health of veterans and emergency service workers. We’re passionate about ongoing education and working with others to implement positive change.

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(Article Edited, Proof Read, and Fact-Checked by Charlotte Officer)

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