SPORT-RELATED CONCUSSION (SRC): Injury without contact to the head
How is the brain injured with no contact to the head/helmet?
In my last blog we explained the mechanisms of injury causing SRC and how the brain moves in reaction to the mechanism of direct impact to the head/helmet, as well as how injury occurs. The mechanism of indirect impact in which there is no contact to the head/helmet causes the head/helmet to move suddenly or violently. This abrupt movement by the head/helmet exerts inertial forces to the brain which can result SRC. Again, sudden acceleration and deceleration of the head/helmet is what causes SRC. This mechanism is referred to as a whiplash brain injury. Let’s explore what is happening to the brain inside the skull with an indirect impact.
Whiplash is defined as an abrupt snapping motion or change of direction resembling the lash of a whip.  Any hit to the body can cause the head and neck to whip in any direction and can cause SRC. The two most common in football are an impact to the quarterback getting ready to pass or a receiver catching a pass. There are two possibilities of brain movement within the skull during these whiplash brain injuries. 1.) The head/helmet and brain continue to move in unison, accelerating at the same speed together until the head/helmet comes to zero velocity and changes direction; or 2) Upon contact, when the body stops moving, the head/helmet (which weighs 12- 13 pounds) accelerates at a faster rate than the brain (which weighs three pounds). 
A receiver comes across the field on a pass route and gets hit in the chest by a defensive back allowing for his head/helmet to continue moving forward. The posterior (or back of the skull) is pushing the brain forward. The head/helmet and brain accelerate together until the head/helmet whips to a stop when the chin is near the chest, reaching zero velocity. The front of the brain (dura mater) has maintained its space with the anterior aspect of the skull until it comes to zero velocity. But the back side of brain separates and continues to compress toward the front side as the head/helmet comes to a stop and begins pushing the brain in the other direction. This compression occurs until the momentum of the entire brain has changed direction. The same thing now happens moving in the posterior direction, but now the brain is being pushed by the anterior side of the skull. This time though, when the head/helmet comes to zero velocity, there is separation between the posterior brain and skull. The brain continues to accelerate toward the skull as it changes direction and comes back and strikes the brain and begins pushing it anteriorly again.
Now, let’s look at what happens if the head/helmet’s momentum causes the head/helmet to accelerate faster than the brain. The posterior skull then pushes the posterior brain forward, but in this case since the brain’s acceleration is less than the head/helmet, the front of the brain begins to separate from the anterior aspect of the skull and compression of brain starts even though both head/helmet and brain are moving in the same direction. When the head/helmet comes to zero velocity and changes direction, it hits the brain and begins pushing it posteriorly until the entire brain brain’s momentum is changed and moving in the same direction. Now the same thing occurs in the posterior direction as described above.
In both scenarios the head/helmet and brain motion continue as described until the head/helmet decelerates and comes to a complete stop. In both, the head/helmet and brain motion of acceleration/deceleration occurs with any indirect impact. The only thing that could change is the direction of movement. The key is that the acceleration/deceleration of the head/helmet is what causes the acceleration/deceleration of the brain inside the skull by pushing the brain.
As with direct impacts, the brain does not bounce back and forth inside the skull with indirect impacts. The brain is pushed back and forth from the acceleration and deceleration of the head/helmet. Therefore, to reduce the risk of SRC we must go beyond the helmet with new technology which slows down the motion of the head/helmet in both indirect and direct impacts. Helmets cannot slow down the head and therefore do not and cannot protect the brain against all forces and energy that act upon it. It is the kinetic energy of the brain’s own motion which elicits forces causing SRC.
There has been much discussion about whether helmets work or don’t work in the protection against SRC. My next blog will discuss what a helmet does and what it does not do. Helmets protect heads. Kato Collar protects brains!
- Whiplash. https://www.dictionary.com/browse/whiplash
- The Size of the Human Brain. https://www.verywellmind.com/how-big-is-the-brain-2794888#