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  • Ben and Kacie

Fight or Flight: Understanding What Happens to the Body After a Car Crash

Updated: Sep 4, 2020

Many injuries that require significant care are not diagnosed in the emergency setting.

An ER physicians’ primary priority is to assess the patient’s condition and determine whether or not he or she needs to be kept in the hospital for further treatment or released with follow-up instructions.

Our body does amazing things to protect itself and to keep us out of harm’s way – and often we do no not even realize its happening. After a traumatic event such as car crash our body goes into “fight or flight” mode.

Here is what this might look like:

At the scene of the accident a person feels she was fine. She felt “shaken up” but did not feel any significant pain anywhere in her body. So she tells police and the other driver that she thinks she is “fine.” She says she does not need paramedics. But as the hours, days, weeks pass…she starts feeling headaches, shoulder pain…neck pain. Why?

This phenomenon is so common that the warns of it as one of the primary concerns “When an Accident Happens”:

“Your first instinct may be to try to minimize the gravity of the situation; however, it’s important to understand that it’s possible to have sustained a personal injury –even if you feel fine at first.” (When to Seek Medical Attention for Personal Injury,

Later, the pain becomes more severe, and the victim goes to the emergency room where she waits for hours to be told she has sprains/strains, whiplash, and a minor concussion. No imaging is done. She is sent home. A few months later we learn she has suffered a torn rotator cuff and a disc protrusion in her cervical spine.  Major injuries.

The purpose of this article is to explain the reasons why people think they are “okay” after a traumatic event even when their injury is severe, and why many musculoskeletal injuries, that later require significant care, are often not diagnosed in the emergency setting.

“Fight or Flight”

In 1915, Walter Bradford Brannon, M.D. coined the term “fight or flight” to describe an animal’s response to threats in bodily changes to a harmful event, attack or threat. (See generally Walter Bradford Cannon, Bodily Changes in Pain, Hunger, Fear, and Rage (New York: Appleton-Century-Crofts, 1929).) The concept explains an automatic physiological reaction in the body that occurs in response to pain, trauma, harm or fear.

When the body’s “fight or flight” response is activated, the amygdala, the area of the brain that contributes to emotional processing, sends a distress signal to the hypothalamus. (Understanding the Stress Response, Harvard Health Publications: Harvard Medical School (Mar. 1, 2011).) The hypothalamus then communicates to the rest of the body through the sympathetic nervous system. The sympathetic nervous system sends signals through the autonomic nerves to the adrenal glands which release hormones into the blood system.

The significance is that this chemical cascade of hormones (primarily epinephrine/adrenaline, noradrenaline, and cortisol) causes the body’s impulses to sharpen and a person’s perception of pain to diminish. The body is preparing us to fight or flee, rather than succumb to pain because of its assessment of imminent harm or stress. The hormones are acting as the body’s natural and immediate pain killer.

“In effect, what is happening, is that the release of these hormones and the increased hormone levels constrict blood vessels to non-vital processes and blunt pain perception,” says Michael Hoaglin, M.D., an emergency room physician at Duke University Hospital. “This fight or flight mode sends us back to our most primal instincts — to focus on what matters to survive the acute situation.”

The Job of an Emergency Medical Physician

It is also important to understand the job of emergency physicians you might visit immediately after a crash, versus primary care doctors or specialists. In the trauma setting, after a crash, ER physicians’ primary priority is to assess the patient’s condition rapidly and accurately, stabilize the patient, and determine whether the patient should be transferred and kept in the hospital for further treatment or released with follow-up instructions. (Michael Rotondo, MD, About Advanced Trauma Life Support, American College of Surgeons.)

On the other hand, emergency room physicians will not always be looking for medical issues that do not present immediate need for treatment or diagnosis. Nonetheless, these conditions are often those which require ongoing care, care of specialists and surgical intervention down the road. 

“Given adequate information about the mechanism of the accident or trauma and immediate state of the patient, most emergency room physicians will give anticipatory guidance for expected pain progression and warning signs of a worsening situation,” says Hoaglin.

Soft-Tissue Injury Does Not Mean Minor Injury

Why does almost every ER record say accident victim suffered “sprains/strains” or “whiplash,” even when imaging later indicates tears, disc bulges, or protrusions?

First, remember the primary concerns of the ER physicians listed above. Even if an ER physician suspects a torn rotator cuff, or ligament tears in the neck, spine or elsewhere, the likely advice will be to follow up with your primary doctor or to see a specialist for further treatment.

Next, it is important to understand the meaning of “soft-tissue injuries.” The American Association of Orthopedic Surgeons (AAOS) breaks soft-tissue injuries into two categories: 1) acute injuries that are caused by sudden trauma that may include sprains, strains and contusions, and 2) overuse injuries that occur gradually over time such as bursitis or tendinitis. (Sprains, Strains and Other Soft-Tissue Injuries, American Academy of Orthopaedic Surgeons.) Ligaments, muscles, joint capsules, intervertebral disks, and cartilaginous endplates can all be classified as types of “soft tissue.” (ACR Appropriateness Criteria, Suspected Spine Trauma,American College of Radiology (1999, rev. 2012).)

AAOS further defines a “sprain” as a “stretch and/or a tear of a ligament.” Sprains are graded 1-3 with a Grade 3 Sprain being a “complete tear of the ligament…” that “causes significant instability and makes the joint nonfunctional.” (Id.) Likewise, AAOS defines a “strain” as an injury to a muscle and/or tendon.  (Id.) Surgery may be required for more serious “sprains” and “strains.” (Id.) Thus, do not be fooled by the phrase sprain/strain in your medical reports. A sprain/strain as diagnosed by an emergency room physician may still be a major injury – it might even require surgery.

Whiplash refers to a “neck injury due to forceful. Rapid back-and-forth movement of the neck. (Mayo Clinic Staff, Whiplash, Mayo Clinic (Jan. 15, 2015))

Symptoms of whiplash can last months or longer, and for some may evolve into chronic pain conditions. Most important, however, is that a diagnosis of whiplash does not rule out other acute injuries to the intervertebral disks or nerves.

Next, it is important to understand which injuries can be visualized in different types of radiological imaging. CT scans and MRIs are advanced imaging technologies used for some injuries. Resources abound for the types of radiological imaging that can, and should, be used to diagnose specific orthopedic injuries. For example, many ligamentous injuries can be seen on an MRI, while some, but not all, can be visualized on a CT absent combining it with an MRI. CT Scans and X-rays are more common in acute trauma emergency rooms than MRIs.

Musculoskeletal Injuries Can Get Worse Over Time

In addition to the “fight or flight” response dulling pain, studies have shown that the delay in symptoms may due to other factors as well. For example, neck pain may develop in subsequent hours, days and even weeks due to the gradual effusion and microscopic hemorrhage in the neck flexor muscles. (Rene Caillet, Neck and Arm Pain (F.A. Davis Co., 3rd Ed., 1991).)

Many musculoskeletal injuries improve with rest, ice and anti-inflammatory medications. However, many others can get worse over time, in part, because they may be difficult to diagnose due to swelling or other more significant acute injuries after trauma. (Michael T. Balla., et al, Commonly Missed Orthopedic Problems, 57 Am. Fam. Physician 267-274 (Jan. 1998).) When not diagnosed and managed early, some musculoskeletal injuries may result in long-term pain and even disabling conditions.


From a physiological perspective, trauma is not a single insult, but a combination of hemorrhage, tissue injury, pain and fear. (B.A. Foex, Systemic Responses to Trauma, 55 No. 4 Brit. Med. Bulletin 726-743 (1999).) It is vital to understand the interplay between the traumatic experience, the injuries, and the initial and continued treatment.


  1. “I am fine” is a natural and expected response after a trauma, however do not be surprised if your pain or injuries worsen over time. Thus, be careful about what you say at the scene of an accident. Your brain may be telling you something that might not last.

  2. Do not expect emergency room doctors to give you a final diagnosis. Their job is to stabilize you and ensure you are not in a life-threatening situation. If you have been in a bad accident, it is always smart to follow up with your own doctors and specialists, especially if you continue to have pain.

  3. The lack of a diagnosis in the emergency room setting is not an indication that there are no major injuries.

  4. “Sprain” and “strain” are broad descriptors of injuries. That does not mean you do not have serious injuries. “Sprain” can mean “tear” and “strain” can mean any injury to a muscle – including tears.

  5. Negative x-rays or CTs do not mean you do not have a serious injury. Instead, remember that certain imaging techniques are better able to visualize certain injuries. Each requires correlation with clinical presentation.

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