SPORT-RELATED CONCUSSION (SRC): What happens inside the skull?
By Dave Norris April 28, 2022
SRC is a traumatic brain injury induced by biomechanical forces; it may be caused either by a direct blow to the head, face, neck or elsewhere on the body with an impulsive force transmitted to the head. [1] To simplify, SRC in football occurs from direct impact that causes contact and inertial forces to the head and from indirect impact that causes only inertial forces to the head. A direct impact to the head/helmet causing the head/helmet to decelerate and accelerate can occur with helmet-to-helmet, helmet-to-shoulder pad, helmet-to-body, or helmet-to-ground forces. An indirect impact is caused when there is no contact with the helmet, but the head/helmet moves suddenly or violently. This can occur with body-to-body impacts causing the head to change direction rapidly. In both cases of direct or indirect impacts, the point of emphasis is that THE HEAD MOVES in the majority of impacts in football. Most experts agree that abrupt acceleration/deceleration of the head is the cause of SRC. But the question to be asked in the prevention of SRC is “What is happening to the brain during acceleration/deceleration of the head?”
DIRECT IMPACTS
If you are following my posts, we learned last week, that based on the structural anatomy of the brain, it is separate from the skull and does not bounce. If the brain does not bounce (even though many are taught that it does), then what does the brain do? One mechanism of direct contact is helmet-to-helmet in which both move with velocity and direction. During contact each helmet comes to zero velocity prior to changing direction and then they accelerate away from each other and reach a new velocity based on their momentum. Does the brain reach zero velocity at the same time as the helmet? Of course not! It is separate from the skull. The brain is still accelerating in the direction of the contact because it is separate from the head/helmet. The part of the brain closest to the point of contact moves into the skull first as the back side compresses. The brain does not begin to decelerate and reach zero velocity at the same time as the head/helmet. It continues in the same direction until the head/helmet changes direction and begins pushing the brain in the opposite direction of contact. The energy that is elicited to the brain is not from the contact, but from its own kinetic energy of motion toward contact site. This push of the brain by the head/helmet continues until the entire brain’s momentum is moving in the same direction as the head/helmet. Important to note: Deceleration of the head/helmet to zero velocity on contact occurs while acceleration of the brain inside the skull continues. One is slowing down, and the other is not.
What happens next? The head/helmet continues to accelerate moving away from the contact pushing the brain until the head/helmet whips to a stop coming to zero velocity. When the head/helmet stops moving, the brain is now accelerating with its own momentum inside the skull. The brain separates from the contact side of the skull and continues in motion with its own velocity in the direction the head/helmet reached its zero velocity. As this motion of the brain occurs, the head/helmet begins accelerating back towards the contact site and hits the brain pushing it in the opposite direction. This continues to occur until the head/helmet stops moving. Important to note: During this second contact of the brain with the skull, the brain is accelerating in opposition to the acceleration of the head/helmet. They are in motion and accelerating toward each other.
All of the mechanisms of injury are what we call SRC, and they occur in less than a second. The head/helmet stops moving in less than a second in most incidences. Does the SRC occur with the first contact of the skull and brain or the second contact? Or do both contribute to the SRC? Based on our previous post about the narrative created by helmet companies and the NFL, it only occurs on the first contact between the skull and brain as the helmet only works during direct contact.
I believe that injury to the brain (SRC) undoubtedly occurs with both the first and second contact of the skull and brain. One could even make the argument that even more force elicited to the brain on the second contact of brain and skull than the first. Here’s why! When a player is setting up to block his opponent on a kickoff return and they hit helmet-to-helmet, the blocker is usually the player who sustains a concussion. The blocker’s head/helmet has very minimal motion and velocity upon contact with the opposing player’s helmet. For all practical purposes, the head/helmet and brain of player blocking on the kickoff are not moving when struck by opponent covering the kick. Therefore, both head/helmet and brain are basically at zero velocity when contact occurs. The direct impact causes the blocker’s head/helmet to move, and the inferior side of the skull pushes the brain in the direction the head/helmet is moving after contact. Important to note: In this first contact of skull to brain the head/helmet is accelerating into the brain which is fairly stationary with little or no acceleration or deceleration. The head/helmet accelerates based on the momentum created by impact and begins pushing the brain. The mass of the head/helmet is 12-13 pounds; it is pushing a 3-pound brain. [2.3] When the head/helmet comes to zero velocity as it whips to a stop the brain is now no longer in contact with the skull and its momentum and acceleration is less than the head/helmet. As the head/helmet comes out of zero velocity, it changes direction and moves back toward the brain, striking the brain which is still moving in the direction the head was moving prior to its change of direction. Important to note: The head/helmet and brain are accelerating toward each other.
Back to the question of does the SRC occur with the first contact of the skull and brain or the second contact? Or do both contribute to the SRC? I believe it is very clear that there are forces elicited to the brain after direct impacts to the helmet that attribute to SRC. It is also apparent that the brain is not bouncing back and forth inside our skulls but is being pushed back and forth by the momentum of the head/helmet after direct impact. Therefore, it is important to understand that movement and speed of motion of the head/helmet after direct impact significantly increases the chance that a SRC can occur. Which is why technology going beyond the helmet is necessary to prevent SRC. The necessary innovation must decelerate the head/helmet after impact.
More support for this necessary technology will come in my next blog which addresses SRC caused by indirect impacts.
Helmets protect heads. Kato Collar protects brains!
- Consensus statement on concussion in sport—the 5th international conference on concussion in sport held in Berlin, October 2016; McCrory P, etal; Downloaded from http://bjsm.bmj.com/ on January 2, 2018 – Published by group.bmj.com;
- The Size of the Human Brain. https://www.verywellmind.com/how-big-is-the-brain-2794888#
- Human Brain: Facts, Functions & Anatomy. https://www.livescience.com/29365-human-brain.html; By Tanya Lewis – Staff Writer September 28, 2018