The brain has a jelly-like consistency and sits within a hard-cased skull; a direct or indirect impact to the head or a whiplash effect will cause the brain to move inside the skull. An impact to the head will involve both linear forces and rotational forces.
Linear forces are direct straight-line forces that compress or stretch the brain within the skull. Rotational forces are angled forces to the head from a ball, head, elbow, knee and ground. Rotational forces twist and shear the brain and brain cells.
Nature did not design the brain for rotational forces and injury, with the brain being badly designed for sudden rotational acceleration and deceleration. In sport the brain is subjected to sudden acceleration and deceleration, because it is rotated from impacts at the side and back of the head e.g., a head to head, head to ball, head to ground contacts and hits.
The white and grey matter of the brain is made up of differing densities, which means the jelly-like brain sections move at different speeds when rotated, this causes twisting of the brain, shearing of brain cells, brain cell death and the disruption of the nerve cell connectivity networks in the brain.
It is repeated rotational forces that cause more significant brain damage than linear forces. Rotational forces cause concussion, increases the risk of diffuse axonal injury (DAI) and to long-term neurodegenerative diseases including Chronic Traumatic Encephalopathy (CTE).
Damage to the brain cells from an impact can be both immediate (damage to the cell structure – as shown in the rotational damage diagram) and delayed (blood flow changes or neural inflammation). Each impact to the brain has the potential to cause an injury that is as visceral as a torn hamstring.
Brain injury happens at the microscopic level, 4,000 times smaller than the eye can see on a regular brain scan. About 40% brain injuries are classified as mild, in that they don’t register concern based on a brain scan, results or dictate a need for a scan when the individual attends A&E immediately after a head injury. Brain injury is not identified because it can’t be seen and recognised by conventional scanning technology.