Fencing Response to Head Injury
Fencing reaction is a visual symptom of concussion caused by traumatic brain injury.

Fencing response or tonic posturing indicates traumatic brain injury. The fencing reaction is a strange and unnatural stance of the arms that is unconsciously adopted by people with a concussion. The forearms are held awkwardly—one flexed and the other stretched into the air for a few seconds after the contact.

  • The term “fencing response” is because the position resembles the on-guard position used in fencing.
  • Movements of the arms usually occur once the individual has lost consciousness, so it is not a conscious reaction; they will not be affected by gravity or momentum.
  • Once the individual regains consciousness, they will resume normal movement of the arms.

The fencing response is thought to be activated in brain injuries caused by soft brain tissue striking the skull's hard bone. This induces gray matter damage and momentarily disables higher brain activity while the brainstem takes control. This might cause an abnormal posture of the arms, which normally lasts a few seconds after the contact.

What are the common signs and symptoms during a fencing response?

Fencing reaction is a visual symptom of concussion caused by traumatic brain injury (TBI). Although the aberrant posture is primarily seen in the forearms, it may be seen in the abdomen and legs.

During a TBI, concussion, and fencing response, a person may exhibit additional warning signs and symptoms, which may include:

  • Clutching of the head/helmet
  • Unsteadiness/swaying in stance
  • Blank expression
  • Confusion
  • Irritability
  • Delay in answering
  • Vomiting

Fencing response is frequently seen in patients who are knocked down or violently hit while participating in full-contact sports such as football, rugby, and boxing, to name a few.

What is fencing reflex?

The term fencing response refers to the asymmetrical tonic neck reflex (ATNR), also known as the fencing reflex, which occurs in newborns.

In newborns, it's a "primitive reflex" that helps them acquire muscular tone, hand-eye coordination, and one-sided body motions. It normally ceases when a baby is four months. Newborn babies position themselves with one arm flexed and the other extended, with their heads, turned toward the extended arm, as if they were trained fencers.

A fencing response occurs after an injury because it is believed that if a blow impacts the brainstem, it will temporarily reactivate ATNR, mimicking the fencing reflex.

What causes a fencing response?

The fencing response state is an obvious sign of brain injury (concussion), which may have resulted from sports or an accident. The nerves that regulate the muscle groups in charge of raising the arm are manually activated by the shock of the trauma

Lateral vestibular nucleus (LVN)

  • LVN has neurons that connect it to motor neurons inside gray matter in the spinal cord. These muscle groups are activated by stimuli so that infants can respond to instincts such as grabbing for their mothers or stopping their falls. 
  • The proximity of LVN to the brain and brain stem connection increases the possibility that a blow to the head could stretch this connection, triggering the fencing response. 
  • Stimulated neurons suppress nearby neurons, preventing them from being stimulated on the opposite side of the body. When under the impact, LVN sends signals to one side of the body that activate motor neurons responsible for extension while suppressing motor neurons responsible for flexing.

Reactivation of asymmetrical tonic neck reflex (ATNR) code

  • Traumatic forces are transmitted into the brain tissue during a concussion or traumatic brain injury (TBI), destroying neurons (brain cells). With enough force, the brainstem (the bottom region of the brain) can be damaged. 
  • The brainstem plays an important function in reflex regulation. As babies, we all have "basic" responses that help in survival. These reflexes disappear or get integrated once we reach developmental stages and no longer require them. 
  • ATNR usually vanishes around the fourth month of birth although the "code" remains in the brainstem. A concussion/TBI with enough force to the brainstem will temporarily reactivate the coding and induce that fencing reflex posture.

Rotational force and the fencing response

  • According to studies, either direct or indirect head contact can result in concussions or TBIs. A concussion or TBI, for instance, can occur when the head is violently whipped around during a car accident (without any other contact, such as with the steering wheel or dashboard). 
  • That's because the rotational forces that the start/stop movement of the head and neck impart on the brain are the leading causes of concussions and TBIs. 
  • Rotational forces may cause the brainstem to twist and torque, as well as pull the brain tissue in various directions (shearing force). Concussions and TBIs with associated rotational forces are more likely to reverberate into the brainstem, activate the ATNR code, and result in the momentary fencing response.

The fencing response state is a clear indicator of injury force to the midbrain that may aid in injury identification and classification.

How does a fencing response help diagnose a patient with traumatic brain injury?

Most doctors theorize that a fencing response may help them diagnose a patient with a concussion or traumatic brain injury (TBI).


  • Because concussions cannot be seen on MRI or CT scans, clinicians must rely on a range of markers and symptoms to diagnose them. One of these signs is the fence response.
  • Concussions are diagnosed by examining eyesight, reflexes, coordination, balance, memory, recall capacity, and observation. 
  • If doctors suspect that the injury has caused bleeding or edema in the skull, they may perform imaging procedures such as a CT scan.
  • According to research, the fencing response is an obvious sign of brain damage, and it is thought to be a more severe injury than when there is no fencing response.

Related to rotation force injury

  • The fencing response indicates a concussion/TBI due to rotational force. Brain tissue and brainstem are particularly vulnerable to shearing and torque caused by rotational forces. This causes more widespread brain tissue damage and a more severe concussion/TBI. 
  • As a result, a fencing response posture indicates a more severe concussion/TBI. It is a clear neurological sign, and the observation of posturing in a patient, if made by a clinician trained in identifying this physical sign, may be used to reach the level of clinical certainty required for a definite concussion determination.
  • Furthermore, this shearing damage can result in diffuse axonal injury. A patient will lose consciousness if the axonal damage is severe enough. 
  • Moreover, if the reticular activating system, a part of the brainstem responsible for sleep/wake cycles, is damaged, the patient will lose consciousness. 
  • The brainstem contains the asymmetrical tonic neck reflex code for the fencing response. It's no coincidence that more than two-thirds of concussions/TBIs that result in loss of consciousness also involve a fencing response when the brainstem is hit with enough force.

When determining the severity of TBI, doctors use various indications, including the 15-point Glasgow coma scale. Medical specialists are seeking new markers to make diagnosis more reliable for a variety of reasons, including the fact that concussions cannot be detected on MRI or CT scans. Fence response may be included as part of the evaluation process because the fencing response is assumed to involve the brainstem.

What is a concussion?

A concussion is a disruption in brain function induced by either direct or indirect impact on the head. It is a minor form of traumatic brain injury characterized by the abrupt development of neurological symptoms that recover spontaneously over a variable period. Many people assume that the major sign of a concussion is loss of consciousness although a concussion can occur without this.

Other concussion symptoms might include:

Physical signs

Cognitive impairment (impairment to thinking or mental processes)

Causes of concussion

A concussion is frequently caused by a head injury, such as a blow to the head or face, or a fall in which the head collides with a hard surface, as well as being shaken. Concussions are frequent in sports, particularly contact sports such as football.

The brain is a jelly-like organ that floats inside the skull in a transparent liquid called the cerebrospinal fluid, which protects it from bumps. A hit to the head might overpower this cushion and bounce the brain against the skull, resulting in brain damage. This can also occur as a result of a fast acceleration or deceleration, such as in a vehicle accident, or when the head and upper body are disturbed.

This damage can impair brain function for minutes, hours, days, or weeks. Occasionally, the collision may cause bleeding into or around the brain. If not recognized and treated promptly, this bleeding can lead to death.

Managing concussion

  • A person with a concussion needs rest both physically and mentally. A person with a minor concussion may not require emergency care, but they should be under observation until their concussion symptoms decrease. 
  • Experts advise avoiding driving or participating in sports for at least 24 hours after an injury and refraining from drinking alcohol or using drugs for one to two days until the symptoms have subsided and the patient feels normal.
  • Symptomatic treatment may be recommended depending on the symptoms.

Recovery in patients with concussion

  • Resting while there are symptoms is typically beneficial to patients with concussions. The majority of concussions (80 to 90 percent) heal in a short (7 to 10 days) period, but the timeframe varies with age.
  • Some symptoms of a brain injury may continue for many weeks, but the individual may become normal within a month. When the person is symptom-free, they should gradually resume social activities.
  • It is harmful to the brain to get injured again before it has recovered from the initial injury; therefore, if a person has prolonged symptoms, they must be evaluated and cleared for a return to activity before gradually returning to sports or work.

If a concussed person vomits repeatedly, experiences an excruciating headache, has a seizure or fits, or is unconscious or if their symptoms worsen, they should be taken to the hospital right away.

Sports-related concussions are thought to occur in the United States annually at a rate of up to 3.8 million. A fall, blow to the head, or severe shaking of the head and upper body can all result in concussions. Concussions can impair brain function and result in a range of symptoms that may need evaluation and monitoring by a doctor.

Subscribe to MedicineNet's General Health Newsletter

By clicking Submit, I agree to the MedicineNet's Terms & Conditions & Privacy Policy and understand that I may opt out of MedicineNet's subscriptions at any time.

Health Solutions From Our Sponsors

Medically Reviewed on 10/14/2022
Image Source: iStock image

Brain Injury Forces of Moderate Magnitude Elicit the Fencing Response: https://citeseerx.ist.psu.edu/viewdoc/download?doi=

The pentagram of concussion: an observational analysis that describes five overt indicators of head trauma: https://bmcsportsscimedrehabil.biomedcentral.com/articles/10.1186/s13102-022-00430-4

The Fencing Response: https://www.healthguidance.org/entry/14309/1/the-fencing-response.html

Concussion: https://www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments/Concussion