Also called acute stress response, fight or flight response is a physiological reaction in case of a perceived threat. It was first described by the American physiologist Walter Bradford Cannon in 1915.
Fight or flight response is governed by the sympathetic nervous system, one of the branches of the autonomic nervous system in charge of largely unconscious mechanisms such as heart rate, digestion, respiratory rate, and pupillary response. Perception of threat triggers the sympathetic nervous system, which brings about various physiological changes to help us survive. The release of hormones such as norepinephrine and epinephrine prepare the body to either stay and deal with the situation (fight) or run away from it (flight).
Increased heart rate, dilation of blood vessels and bronchi, increased conversion of glycogen to glucose, dilatation of the pupils are some of the changes caused by the fight or flight response. These cause an increase in blood flow and increased oxygen availability in the blood, increased oxygen and energy availability to the heart and muscles, and improved visual acuity to assess the threat better.
The fight or flight response may be triggered when facing a physical threat such as a growling dog. However, in our daily lives, it is more likely to be falsely triggered in the absence of imminent danger and instead due to a psychological source of stress, such as having to give a big presentation. In that case, the physiological changes that help us survive during a real threat become a source of anxiety and stress.
Although fight or flight response and the changes caused by it are primarily autonomic functions, there is a way to calm the body down: Breathing. By intentionally taking deeper, slower, diaphragmatic breaths, we can slow down our heart rate and help to put the brakes on the acute stress response.
Deeper breaths, especially diaphragmatic breaths, help to trigger the opposite response called rest and digest, which is governed by the parasympathetic nervous system, another branch of the autonomic nervous system. You may be suffering from severe anxiety and panic disorders, or you may just want to manage daily stress more effectively. Learning about the fight or flight response and turning to relaxing breathing exercises could help you.
You can find more on relaxing breathing exercises here.