The fencing response occurs when a neck reflex is reactivated after a head injury. Doctors use the fencing response to help determine the severity of a traumatic brain injury.

If you experience an impact that’s strong enough to cause traumatic brain injury, such as a concussion, your arms often go into an unnatural position.

This position — forearms extended or flexed, usually in the air — follows the impact and is known as the fencing response position. It lasts up to several seconds after the collision.

The fencing response is often seen when a player is knocked down or knocked out during full-contact athletic competitions such as football, martial arts, boxing, rugby, and hockey.

This article examines why the fencing response occurs and how it can help a doctor diagnose the severity of a brain injury.

The name “fencing response” comes from its similarity to the asymmetrical tonic neck reflex, also known as the fencing reflex, which occurs in newborns.

This is when newborn babies position themselves with one arm flexed and the other extended, with their heads turned toward the extended arm like a trained fencing athlete.

This reflex usually stops occurring after the baby reaches approximately 4 months.

Doctors believe that the fencing response may occur after a head injury because the blow affects the brainstem, which temporarily reactivates the asymmetrical tonic neck reflex seen in newborns.

Doctors use several indicators, such as the Glasgow coma scale, to assess the severity of traumatic brain injuries.

For a variety of reasons, including the fact that concussions can’t be seen on MRI or CT scans, medical professionals are looking for more indicators to make their diagnoses more accurate.

A fencing response, if seen by witnesses, has become part of the assessment process.

A fencing response that occurs after an injury is likely worse than an injury where no response occurred. This is because a fencing response is thought to involve the brainstem.

A 2009 study that reviewed over 2,000 YouTube videos of high impact knockout videos concluded that two-thirds of head impacts demonstrated a fencing response.

And a more recent 2023 study found that the fencing response could be used as an indicator or “red flag sign” of traumatic brain injury.

A concussion is a mild traumatic brain injury that results from a blow to the head or body that causes your brain to twist or bounce inside the skull.

If you think you might have experienced a concussion, you should see a doctor or receive emergency medical assistance immediately.

Signs of a concussion include:

Severe traumatic brain injuries

A severe traumatic brain injury is an emergency situation. Treatment focuses on preventing death, stabilizing the spinal cord, heart, lungs, and other vital organs, and ensuring oxygen delivery and breathing.

A person with severe brain injury may also need surgery to relieve pressure inside the skull.

The fencing response has become a helpful tool for determining the severity of a traumatic brain injury.

If you feel that you’ve experienced an impact that could have resulted in a traumatic brain injury, see a doctor.

Depending on the severity of your injury, a doctor might refer you to an expert such as a neurosurgeon, neurologist, or neuropsychologist.