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Fight-or-flight is the acute stress response first described by Walter Cannon in 1915, in which a perceived threat triggers coordinated activation of the sympathetic nervous system and adrenal medulla. Within seconds, epinephrine and norepinephrine flood the bloodstream, raising heart rate, diverting blood to skeletal muscle, and mobilising glucose to fuel immediate defensive action.
The original model, derived largely from male subjects, does not capture the tend-and-befriend pattern observed in females, mediated partly by oxytocin rather than catecholamines alone.
How it works
The response unfolds in two overlapping waves. The first is immediate: within seconds of a perceived threat, the hypothalamus triggers the sympathetic-adrenal-medullary (SAM) axis, releasing epinephrine and norepinephrine from the adrenal medulla into circulation 12. The catecholamine surge produces a coordinated peripheral cascade: cardiac output climbs, bronchodilation allows greater oxygen intake, blood is shunted away from the skin and gut, and glycogenolysis in the liver raises circulating glucose for immediate fuel.
The second wave runs on a slower timescale, taking minutes rather than seconds. The hypothalamus releases corticotropin-releasing hormone; the anterior pituitary responds with ACTH; the adrenal cortex releases cortisol, which sustains the arousal state and suppresses non-essential immune and digestive activity 2. Together, the two axes constitute what Cannon termed the sympathoadrenal axis, the first formally described integrated nervous-hormone unit in physiology 1.
Cannon's original model was built primarily on male subjects and framed fight or flight as the universal stress response. Taylor et al. showed that a distinct pattern, characterised by affiliation and nurturing behaviour, is common in females and is mediated partly by oxytocin rather than catecholamines alone 3. This tend-and-befriend pattern extends the conceptual framework without displacing the core SAM-axis mechanism.
Example
A competitive athlete standing behind the starting blocks at a major event will notice an elevated heart rate, heightened sensory alertness, and muscle tension before the signal fires. The SAM axis has already engaged: epinephrine is circulating, glucose is elevated, and non-essential functions have been deprioritised. The body is prepared to move at maximal output the moment the starting signal arrives.
Pre-competition arousal is the fight-or-flight system operating as designed; the practical question is whether that arousal remains regulated or becomes overwhelming.
Why it matters
The fight-or-flight response evolved to handle acute, time-limited physical threats. The system does not distinguish between a predator and a sustained period of professional pressure. Chronic psychological stressors keep the SAM axis in a state of sustained activation, producing hypertension, immune dysregulation, and disrupted sleep 2. Because the response carries no built-in termination signal for non-physical threats, the arousal that is adaptive in a short sprint becomes pathological across months of unrelenting activation.
Cognitive costs compound the physiological ones. Across 113 studies, acute stress produced a medium-to-large impairment in working memory and cognitive flexibility 4, capabilities central to sound decision-making under pressure. For the high-performance individual, this trade-off is concrete: the catecholamine surge that primes physical performance simultaneously degrades the prefrontal executive functions required to adapt tactics, read a situation accurately, and avoid impulsive error.
What triggers the fight-or-flight response?+
Any stimulus perceived by the brain as threatening can trigger the response, including physical danger, social threat, and psychological anticipation of harm. The hypothalamus activates the sympathetic nervous system within seconds of threat detection, releasing epinephrine and norepinephrine regardless of whether the danger is physical or imagined.
How long does a fight-or-flight response last?+
The initial SAM-axis surge peaks within minutes. Catecholamines are cleared from the blood relatively quickly, typically within 20 to 30 minutes, though the slower HPA-axis component extends the response via cortisol, which can remain elevated for hours. Recovery to baseline depends on whether the perceived threat has resolved.
Does fight-or-flight differ between men and women?+
Cannon's original model was derived largely from male subjects and emphasises fight or flight as the dominant stress response. Taylor et al. documented a distinct pattern in females, characterised by affiliation and nurturing behaviour (tend-and-befriend), mediated partly by oxytocin. Both patterns activate the SAM axis; the behavioural expression differs.
How does fight-or-flight affect thinking and decision-making?+
Acute stress produces a medium-to-large impairment in working memory and cognitive flexibility, replicated across 113 studies. The catecholamine surge that prepares the body for physical action simultaneously impairs the prefrontal functions needed for deliberate, adaptive decision-making. High stress may preserve reaction speed while degrading strategic judgement.
