New study reveals number and strength of head impacts, not concussions, drive CTE risk in football


June 21, 2023

Does a football player’s number of concussions drive the risk of developing chronic traumatic encephalopathy (CTE)? In a new study of 631 deceased football players, the largest CTE study to date, scientists found that the number of diagnosed concussions alone was not associated with CTE risk. Instead, football players’ odds of developing CTE were related to both how many head impacts they received and how hard the head impacts were.

The study, conducted by researchers at Mass General Brigham, Harvard Medical School, and Boston University (BU), was published today in Nature Communications. It used an innovative new tool called a positional exposure matrix (PEM) that synthesized data from 34 independent studies to estimate the number and severity of football players’ head impacts over their careers. 

“These results provide added evidence that repeated non-concussive head injuries are a major driver of CTE pathology rather than symptomatic concussions, as the medical and lay literature often suggests,” said study senior author Jesse Mez, MD, MS, Associate Professor at the BU Chobanian and Avedisian School of Medicine and Co-Director of Clinical Research at the BU CTE Center.

The new data could provide football with a playbook to prevent CTE in current and future players, according to researchers. 

“This study suggests that we could reduce CTE risk through changes to how football players practice and play,” said study lead author Dan Daneshvar, MD, PhD, Assistant Professor at Harvard Medical School and Physician at Mass General Brigham affiliate Spaulding Rehabilitation. “If we cut both the number of head impacts and the force of those hits in practice and games, we could lower the odds that athletes develop CTE.”

The researchers used the new PEM tool to estimate the cumulative number of head impacts, and the cumulative linear and rotational accelerations associated with those impacts, based on the levels and positions athletes played throughout their football career. The study found that cumulative repetitive head impact (RHI) exposure was associated with CTE status, CTE severity, and pathologic burden in the football players. Additionally, the study found that models using the intensity of impacts were better at predicting CTE status and severity than models using duration of play or number of hits to the head alone.

The PEM is a valuable tool that researchers can utilize to improve studies on risks of football play. By using the PEM in future studies, researchers could look at other potential effects of RHI exposure beyond CTE to gain a better understanding of the specific types of RHI that are most likely to cause these problems. 

“Although this study was limited to football players, it also provides insight into the impact characteristics most responsible for CTE pathology outside of football, because your brain doesn’t care what hits it,” said Daneshvar. “The finding that estimated lifetime force was related to CTE in football players likely holds true for other contact sports, military exposure, or domestic violence.”

A limitation of the study is that it utilized a convenience sample of football-playing brain donors who tended to have higher exposure to RHI than the general population of football players. However, a substantial number of donors had lower exposures, so the findings can still be extrapolated to most football players. 

The study was supported by grants and funding from the National Institutes of Health, Department of Veterans Affairs, Department of Defense, the Alzheimer’s Association, the Nick and Lynn Buoniconti Foundation, the Concussion Legacy Foundation, the Adlinger Foundation, World Wrestling Entertainment Inc.


D.H.D. serves as an expert witness in legal cases involving brain injury and concussion and serves as an advisor and options holder for StataDx outside the submitted work. C.J.N. is the cofounder and chief executive officer of the Concussion Legacy Foundation; reported nonfinancial support (travel reimbursement) from the NFL Players Association as a member of the Mackey-White Health & Safety Committee, WWE, and AEW (All Elite Wrestling); and serves as an advisor and options holder for Oxeia Biopharmaceuticals, PreCon Health, and StataDx outside the submitted work. R.C.C. reported royalties from Houghton Mifflin Harcourt; compensation for expert legal opinion to the National Collegiate Athletic Association and National Hockey League; consults for the Concussion Legacy Foundation; is senior advisor and paid consultant to the NFL Head Neck & Spine Committee; is a member of the Mackey-White Committee of the National Football League Players Association; is vice president of National Operating Committee on Standards for Athletic Equipment and chair scientific advisory committee and cofounder of Medical Director Concussion Legacy Foundation; and is on the Medical Science Committee for the National Collegiate Athletic Association Student-Athlete Concussion Injury Litigation. R.D.Z. receives royalties from Oakstone for an educational CD (Physical Medicine and Rehabilitation: A Comprehensive Review) and from demosMedical, part of Springer Publishing, for serving as co-editor of the text Brain Injury Medicine and serves on the Scientific Advisory Board of Oxeia Biopharma, BioDirection, ElMINDA, and Myomo. He is also PI on a grant entitled the Football Players Health Study at Harvard University, which is funded by the National Football League Players Association (NFLPA) and evaluates patients for the MGH Brain and Body TRUST Center, sponsored in part by the NFLPA, and serves on the Mackey-White Health and Safety Committee. L.E.G. is a paid consultant to Johnson & Johnson, Janssen Research & Development LLC, and Rebiscan Inc and has received funding from the WWE and Ivivi Health Sciences. D.I.K. reported royalties from Springer/Demos Publishing for a textbook on brain injury; serves as an expert witness in legal cases involving brain injury and concussion; receives a stipend from Encompass Health as program medical director for brain injury and chair of the annual Neurorehabilitation conference; and has received honoraria for a keynote address for the HealthSouth Annual Medical Directors Meeting. R.A.S. reported personal fees from Biogen and Lundbeck outside the submitted work; member of the Mackey-White Committee of the National Football League Players Association; receives royalties for published neuropsychological tests from Psychological Assessment Resources Inc; and is a member of the Board of Directors of King-Devick Technologies. M.L.A. receives royalties from Oxford University Press for a textbook outside the submitted work. A.C.M. is a member of the Mackey-White Committee of the National Football League Players Association and reports other funding from Buoniconti Foundation during the conduct of the study. No other authors have competing interests as defined by Nature Portfolio, or other interests that might be perceived to influence the results and/or discussion reported in this paper.

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