Study – Mileage (More-so Than Concussions) Predict Long Term Brain Risk in Contact Sports

Yes concussions are bad.  Yes multiple concussions can lead to CTE and other brain dysfunction but concussions are not the be-all end-all risk factor when it comes to adverse brain health in contact sports.  Studies are showing that cumulative sub concussive hits take their toll as well and can be a greater predictor of future cognitive dysfunction and a new study bolsters this understanding.

The recent study, published this week in the Journal of Neurotrauma, showed the more cumulative head impacts athletes received over their sporting career the greater risk for cognitive impairment in later life including executive dysfunction, depression, apathy and behavioral dysregulation.

The Washington Post, who interviewed one of the study’s co-authors, reported as follows with respect to the significance of their findings –

“There has been a tremendous amount of growth in the last several years in the prevention, detection, and management of symptomatic concussions across all levels of play and all sports. That’s fantastic,” said Robert Stern, a professor of neurology at Boston University, director of clinical research at the school’s CTE Center and one of the paper’s co-authors. “The problem is that the focus on concussion has taken away from an appropriate discussion about the more common subconcussive trauma.”…

The mean number of total impacts for the men in the study was 7,742, and those with a higher CHII figure reported higher instances of cognitive, mood and behavioral impairments. Results suggested the CHII figure served as a better predictor of these later-life issues than other metrics, such as concussion history, starting age of football career or length of career.

“We need to take very seriously the notion that hitting your head over and over again may have long-term consequences,” Stern said.

Researchers were able to identify a threshold for players, and continued exposure to head trauma after that threshold resulted in a dramatic increase in risk. Going from 6,500 cumulative hits, for example, to 12,000 “increased the risk for objective cognitive impairment by a considerable twenty-five fold,” according to the study.

“The number of hits that are found to serve as a threshold are not meant to be interpreted as, ‘Wow, I’ve reached that magic number, so I should stop,’ ” Stern said. “There is no magic single number for any given individual. There might be some people who have many, many times the number of hits and do just fine later in life. And there may be many people who have far fewer hits and experience significant problems later in life.”

This study is consistent with previous studies showing that mileage, not necessarily concussions, are one of the biggest factors in long term brain trauma in combat sports such as boxing.  This is a reality regulators, athletes and trainers alike need to come to terms with when it comes to issues such as licencing, smart training methods (ie no ‘gym wars’) and retirement.

This week’s study (which can be purchased here) is titled “Cumulative Head Impact Exposure Predicts Later-Life Depression, Apathy, Executive Dysfunction, and Cognitive Impairment in Former High School and College Football Players“.

The full Abstract reads as follows –

Repetitive head impacts (RHI) refer to the cumulative exposure to concussive and subconcussive events. Although RHI is believed to increase risk for later-life neurological consequences (including chronic traumatic encephalopathy), quantitative analysis of this relationship has not yet been examined due to the lack of validated tools to quantify lifetime RHI exposure. The objectives of this study were: 1) to develop a metric to quantify cumulative RHI exposure from football, that we term the cumulative head impact index (CHII); 2) to use the CHII to examine the association between RHI exposure and long-term clinical outcomes; and (3) to evaluate its predictive properties relative to other exposure metrics (i.e., duration of play, age of first exposure, concussion history). Participants included 93 former high school and collegiate football players that completed objective cognitive and self-reported behavioral/mood tests as part of a larger ongoing longitudinal study. Using established cut-off scores, we transformed continuous outcomes into dichotomous variables (normal versus impaired). The CHII was computed for each participant and derived from a combination of self-reported athletic history (i.e., number of seasons, position(s), levels played), and impact frequencies reported in helmet accelerometer studies. A bivariate probit, instrumental variable model revealed a threshold dose-response relationship between the CHII and risk for later-life cognitive impairment (p<0.0019), self-reported executive dysfunction (p<0.0003), depression (p<0.0009), apathy (p<0.0040), and behavioral dysregulation (p<.0001). Ultimately, the CHII demonstrated greater predictive validity relative to other individual exposure metrics.


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