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Understanding the Fight or Flight Response

The fight or flight response is a natural physiological reaction to stressful situations. It helps humans to respond quickly to threats, however when triggered by normal daily stressors, it can cause long term problems for both physical and mental health.

What is the Fight or Flight Response?

The fight or flight response, also known as the stress response, is a survival mechanism that humans evolved to react quickly to life threatening situations. It is an instantaneous series of physiological responses that help a person deal with a threat, either by fighting it off, or fleeing to safety.

The idea of the fight or flight response was first put forward in 1915 by American physiologist Walter Bradford Cannon in the book Bodily Changes in Pain, Hunger, Fear And Rage. He observed the response in animals when threatened, which was to release the hormone adrenaline and go through a series of changes in the body which resulted in additional oxygen being delivered to the muscles, allowing the animal to have more energy for fighting off the predator or running away.

Since then, other researchers have refined our understanding of this natural response and studied the psychological responses in humans that coincide with these physiological changes.

What is the Freeze and Fawn Response?

In more recent years, psychologists have agreed that a third response that humans use to protect themselves is to freeze. This is also called attentive immobility, or reactive immobility. It causes people to stay completely still as the body takes in information and prepares for the next move. Typically, this freeze response is followed by either a fight or flight response, but it can happen independently. Dr Stephen Porges, describes shutdown in Polyvagal Theory, this can happen when the autonomic nervous system is activated.

Physiological Reaction

When the fight, flight or freeze response is activated, it causes a cascade of hormonal changes in the body that produce physiological responses. The sympathetic nervous system is activated, and several body systems are affected.

  • The heart rate increases, resulting in increased blood flow and more oxygen to the heart and muscles
  • Dilation of bronchi in the lungs leads to an increased respiration rate
  • The liver converts glycogen to glucose more rapidly
  • Blood flow is diverted from non-essential parts of the body, making the skin appear paler
  • Pupils dilate, allowing in more light for improved visual ability.

In addition, the brain can allow a person under threat to focus their attention more keenly on the source of the threat and avenues for escape.

When to Seek Help

The fight, flight, or freeze response is a natural and important part of human evolution which allows us to survive in threatening situations. However, in the modern world, this response can sometimes be activated by stressors which are not life-threatening. Stressful situations such as work pressure, running late, or a fight with a partner can all trigger this cascade of physiological responses.

In the long term, repeated activation of the stress response causes problems such as high blood pressure and problems sleeping. It can also contribute to depression, anxiety, and other mental health issues.

If you recognise that your body is regularly responding to situations with some of the physiological changes listed above, it is a good idea to speak with an experienced psychotherapist who can assist you to find ways to more accurately perceive levels of threat to avoid ongoing anxiety and to more effectively manage hypervigilance and your stress response.


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