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The Physiology of Combat Stress Reaction

This article discusses how intense combat stress may result in extreme physiological reactions that become so overwhelming they affect your ability to function during the event, and may also be re-experienced after the event is over, sometimes for many years.

What a Combat Stress Reaction May Look Like

During an intense firefight in Afghanistan, a soldier became confused and disoriented, and began recklessly charging up and down the field between his unit and the enemy. The medic found the soldier's heart rate and blood pressure were dangerously high and he was taken to an aid station. After some rest and reassurance, his heart rate slowed and he returned to his normal state. He was returned to duty the next day.

This story from a forward-deployed mental health provider is an example of a Service Member experiencing an extreme combat stress reaction, also known as a CSR. CSRs are intense but predictable responses to extreme life-threatening combat stressors, or put another way, considered "normal" responses to abnormal events. CSRs may look different in different people, and symptoms can include a "power up" response with a dramatically increased heart rate, agitated behavior, intense anger or fear, and a single-minded focus on the threat. Conversely, CSRs can include a shutdown response with lower heart rate and blood pressure, frozen behavior, numb emotions, and detachment from surroundings and the mission.

How our Body Responds to Life-threatening Combat Stressors

Our bodily systems like to maintain a state of balance, in which bodily functions are running optimally. Typically, our heart rate, hormones, oxygen level, body temperature, etc., are all perfectly balanced under non-stressful conditions. Stressors, or stressful situations, may knock us out of balance, and extreme stress may knock us extremely out of balance.

When you encounter a life-threatening situation in combat, your body's first instinct is survival. Our autonomic nervous system (ANS) manages our body's response to stress, and has two parts: the sympathetic nervous system (SNS) – the arousal, or "power up" system, and the parasympathetic nervous system (PNS) – the shutdown, or "power down" system. Under extremely stressful conditions, our bodies can naturally power up or power down to an extreme. If you are in a combat setting, these reactions can help you survive, fight, find cover, or escape. But it's possible the reactions may be so extreme they impair your operational performance, which may also affect the unit. A recent study reported 51.7% of Soldiers previously deployed to Iraq or Afghanistan said they encountered team members who were so mentally stressed during combat they were unable to function for a period of time.

Where Do You Go from Here?

CSRs are hardwired survival responses triggered by the ANS; the reactions are instant, automatic survival reactions to life-threatening situations. Understanding this biological process can help you recognize a CSR in yourself and in other Service Members. It can also help you realize anyone exposed to life-threatening combat stressors can experience a CSR and it is not a sign of weakness.

If you experienced a CSR while deployed and you have been re-experiencing the event with some of the reactions listed above, there might be a connection between these occurrences. You may also be at risk for experiencing another CSR if you deploy again or participate in a combat-related field operation. Working with a mental health provider can help you break the link between the past CSR and any current re-experiencing, and lower the risk of a future CS

Talk to a Professional and Get Support

Reach out to a health care professional if you need additional support, show signs of CSR, or for any other mental health support. For immediate help, call the Military & Veterans Crisis Line by dialing 988 and selecting Option 1 or the Disaster Distress Helpline at 800-985-5990. The inTransition program is standing by 24/7/365 to help Service Members and veterans get connected to care in their area. Military OneSource is another great resource for service members and their families who may need support. Lastly, call the Psychological Health Resource Center at 866-966-1020 or use the Real Warriors Live Chat for help accessing care and resources.

For immediate help, especially when feeling suicidal, call:

Additional Resources:


  1. Adler, A. B., Svetlitzky, V., & Gutierrez, I. A. (2020). Post-traumatic stress disorder risk and witnessing team members in acute psychological stress during combat. BJPsych open, 6(5), e98.
  2. Sapolsky, R. M. (2004). Why zebras don't get ulcers: The acclaimed guide to stress, stress-related diseases, and coping. Holt paperbacks.
  3. Taylor, M. K., Mujica-Parodi, L. R., Padilla, G. A., Markham, A. E., Potterat, E. G., Momen, N., ... & Larson, G. E. (2009). Behavioral predictors of acute stress symptoms during intense military training. Journal of Traumatic Stress: Official Publication of The International Society for Traumatic Stress Studies, 22(3), 212-217.
Last Updated: December 19, 2022
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