Routine Football Hits Cause Damage to the Brain: Study

Football just can’t seem to catch a break.

It seems like almost daily that another research study comes out warning of the dangers of football to the brain.

We’ve learned to accept that big, crushing hits may cause concussions and other brain injuries. We’ve changed the rules, the helmets and our approach to blocking, tackling and other hits.

Then along comes a brand new study by the folks at Carnegie Mellon University (CMU) that says concussions and concussive contact isn’t the only thing in football causing damage to players brains.

According to the folks at CMU and the University of Rochester Medical Center, a season of typical football hits can cause structural changes in the brains of players.

Their study was just published in the journal Science Advances. It involved 38 University of Rochester (Division III) football players who received brain scans before and after the season. The players wore accelerometers, which are devices which measure accelerative forces, inside their helmets. The devices were worn for every practice and every game for the entire season.

In that season, two of the players were clinically diagnosed with concussions. However, when researchers compared the pre- and post-season MRIs, it was revealed that more than 2 of every 3 players showed a reduction in the structural integrity of their brains. The MRIs showed reduced white matter integrity in the midbrain after the season, when compared to the pre-season scans. They were able to tie the injuries directly to football by correlating the amount of white matter damage with the number of hits to the head the players sustained.

“Public perception is that the big hits are the only ones that matter. It’s what people talk about and what we often see being replayed on TV,” said senior study author Brad Mahon, an associate professor of psychology at Carnegie Mellon and scientific director of the Program for Translational Brain Mapping at the University of Rochester. “The big hits are definitely bad, but with the focus on the big hits, the public is missing what’s likely causing the long-term damage in players’ brains. It’s not just the concussions. It’s everyday hits, too.”

The midbrain is located in the center of the head, just below the cerebral cortex. Along with the brain stem and thalamus, it makes up a larger, rigid, stalk-like structure. It is biomechanically susceptible to the forces of head hits due to its relative rigidity. It absorbs force differently than the surrounding, softer brain tissue. It is important for functions which include eye movements. Eye movement is often acutely effected by concussions and head hits.

We know that head contacts impact many parts of the brain simultaneously. However, researchers believed the midbrain would be a strong indicator of problems caused by sub-concussive hits.

“We hypothesized and found that the midbrain is a key structure that can serve as an index of injury in both clinically defined concussions and repetitive head hits,” said Adnan Hirad, an M.D./Ph.D. candidate at the University of Rochester’s Medical Scientist Training Program and lead author of the study. “What we cataloged in our study are things that can’t be observed simply by looking at or behaviorally testing a player, on or off the field. These are ‘clinically silent’ brain injuries.”

Players in the study each received MRI scans within two weeks of the season beginning and within one week of it’s end. Accelerometers in the helmets measured linear and rotational acceleration during all practices and games, recording all contact that produced forces of 10 gs or greater.

By comparison, space shuttle astronauts experience only 3g’s of force during lift-off. Race car drivers can be exposed to 6g’s. A car crash can produce forces of more than 100g’s for very brief periods of time.

The 38 players experienced nearly 20,000 hits across all practices and games. Of those hits, the median force was around 25 gs, with half of the hits exceeding that amount. Only two of the nearly 20,000 hits resulted in concussions.


“We measured the linear acceleration, rotational acceleration and direction of impact of every hit the players sustained. This allowed us to create a three-dimensional map of all of the forces their brains sustained,” Hirad said.

By using the MRI scans, researchers were able to measure and map structural changes in the brains of the athletes which took place over the course of each season. They discovered that there is a stronger correlation between rotational acceleration, or impact causing the head to twist, and the observed changes in the structural integrity of the white matter in the midbrain than that between linear acceleration, or head-on impact and the changes.

“This study suggests that midbrain imaging using diffusion MRI might be a way in the future to diagnose injury from a single concussive head hit and/or from repetitive sub-concussive head hits,” said Dr. Jeffrey Bazarian, professor of Emergency Medicine, Neurology, Neurosurgery and Public Health Sciences at the University of Rochester Medical Center and a co-author of the study.

The second part of the study served as an independent means to validate the researchers’ approach to the football cohort. This group included 29 athletes from various other contact sports who had suffered clinically defined concussions and 58 who didn’t.

Those participants who’d had concussions underwent MRI scans and had blood samples taken within 72 hours of their injury. The researchers found reductions in the integrity of midbrain white matter in these athletes. The degree of reduction was similar to the football players in the study. They also found increased levels of tau, a specific protein, in their blood. Tau levels rise as structural integrity in the brain decreases.

“Tau is an important marker of acute changes in the brain and is thought to be, in the long term, implicated in neurodegenerative diseases like chronic traumatic encephalopathy, also known as CTE,” Hirad said.

Given this new insight on repetitive head hits, what should be done?

“Our research, in the context of prior research over the past several years, is beginning to indicate that the accumulation of many sub-concussive hits is instrumental in driving long-term damage in football players’ brains,” Mahon said. “Future research will be required in order to translate our findings into concrete directives that are relevant to public health. An important direction for future research will be to carry out larger-scale longitudinal studies of contact sports athletes in various ages groups.”

“We also need to re-evaluate how we make return-to-play decisions,” Hirad said. “Right now, those decisions are made based on whether or not a player is exhibiting symptoms of a concussion like dizziness or loss of consciousness. Even without a concussion, the hits players are taking in practice and games appear to cause brain damage over time.”

While football gets the spotlight, other sports also lead to hits to the head, as well as other sub-concussive head and neck trauma. It would be useful to study those to see if similar outcomes are found.

In the meantime, it seems football keeps getting “kicked in the head” (pardon my humor) when it comes to head trauma, brain injury and concussion. Even with advances in equipment, we keep discovering new and often more disturbing problems with the contact in this sport.

As a fan of the game, it’s my hope that research leads to better ways to manage the impacts and their effects. If not, football may be seeing it’s last down.

Keep the faith and keep after it!

Success! You're on the list.

Journal Reference – Adnan A. Hirad, et al., A common neural signature of brain injury in concussion and subconcussion. Science Advances, 2019

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.