Bumps and head injuries are common among military personnel and people who regularly engage in contact sports such as football, rugby, boxing and wrestling, and those facing physical violence. A recent study published in Nature Communications finds that the cumulative intensity of head injuries could lead to a neurodegenerative health condition called chronic traumatic encephalopathy. It leads to changes in memory, cognition and behaviour in the individual.
“It has been previously known that repeated hits to the head could cause problems like loss of memory (dementia) later in life,” Dr Daniel H Daneshvar, first author and assistant professor at the Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, USA, tells Happiest Health.
“But we did not know what characteristic of those hits to the head were most associated with chronic traumatic encephalopathy, and that is what we wanted to find out,” he adds.
Chronic traumatic encephalopathy causes changes in behaviour, cognition and motor symptoms. It includes impulsiveness, rage, paranoia, memory deficits, impaired attention, dysphagia (difficulty in swallowing), dysarthria (difficulty in speaking) and coordination problems.
Chronic traumatic encephalopathy begins in the cerebral cortex and, over time, progresses slowly to other brain regions such as the medial temporal lobe, basal ganglia and brainstem.
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The football model
The study was conducted at the Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston. The researchers used American football as a model for a repetitive head injury.
“People start playing American football at different ages and have different career lengths. Based on the different positions (defensive line to forward line) and the levels of their play (pre-high school to professional), they get different characteristic types of frequencies and intensities of impacts on the head,” explains Dr Daneshvar.
The researchers collected American football helmet sensor data from previously published research articles. Helmet sensors measure the different head impact features, such as the number and intensity of impacts (as linear and rotational acceleration).
Increasing linear forces are generally associated with localised damage to the brain. Rotational forces may cause brain damage due to brain tissue rubbing against the skull.
Based on this data, they created a position exposure matrix (PEM) to quantify the repetitive head impact specific to player position and level of play. This matrix was used to measure the estimated repetitive head impacts in a group of 631 football-playing brain donors in their lifetime.
History of head impacts
Data about the brain donors were obtained from the Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) and Framingham Heart Study (FHS) Brain Banks. All brain donors were former football players with a history of repetitive head impact exposure through contact and collision sports, military service or domestic violence.
A clinical history was also obtained from informants (next of kin) about the donors’ behaviour, mood, cognition and motor symptoms. Clinical examination of the brain tissue samples was also performed to determine the presence and severity of chronic traumatic encephalopathy in them.
The clincher
They found that out of 631 athletes, 451 had developed chronic traumatic encephalopathy due to having more hits to the head and greater force (intensity of hit) compared to those who did not develop this condition.
The number of hits as well as the force intensity were higher in those with high-stage chronic traumatic encephalopathy than those with a low-stage condition.
These results suggested that the intensity of impacts experienced during an entire lifetime plays an essential role in the development of chronic traumatic encephalopathy and its severity than the duration of play or the number of head impacts alone.
All hits matter
“The total force to the head that the players experienced over their life best predicted the development of chronic traumatic encephalopathy development and its severity,” says Dr Daneshvar. In other words, the total number of hits and the force of those hits together result in chronic traumatic encephalopathy.
All the hits matter, he says, regardless of whether they cause a concussion (mild brain injury) or not.
He says the results give a game plan for preventing chronic traumatic encephalopathy among athletes, military veterans and individuals exposed to repetitive head impact.
“If we can reduce the total force to the head associated with these activities, we can reduce chronic traumatic encephalopathy risk,” emphasises Dr Daneshvar.
