Repetitive Head Impacts: A Major Concern At All Levels of Sports
Are rules gradually increasing the amount of contact next?
Many states have also enacted rules changes establishing a progression up to full-contact in preseason practices, similar to the heat acclimatization schedules integrated into preseason workouts in recent years. For example, the Illinois High School Association (IHSA) limits equipment to helmets only during the first two days of practice, helmets and shoulder pads the next three days, with full pads only being introduced on the sixth day of the acclimatization period. Similar progressions have also been adopted in Alabama, Minnesota, Kansas and Florida, among others.
Interestingly, a recent study by Purdue researchers provides support for such a progression. finding that cerebrovascular reactivity (CVR) – a measure of the ability of blood vessels in the brain to dilate to compensate for increased levels of carbon dioxide in the blood, such as occurring during exercise – was significantly reduced in almost all football athletes during the first six weeks of the contact season, findings which the researchers viewed as demonstrating that the onset of subconcussive blows had “at least a transient effect on the brain, but also suggest[ing] that the brain can adapt to [the contact] with an eventual return to baseline.”
The researchers expressed concern that athletes may be at risk of incurring symptomatic injury during period their brains were trying to adapt to contact at the beginning of the season. Noting that in most states football teams typically switch from limited contact levels during the preseason to two practices a day, at least one of which includes contact, they expressed concern that, based on their findings, “the brain may not be able to adjust quickly to this change, leaving players at increased risk for injury” at the beginning of the football season. They thus suggested that it might be better for teams to increase the amount of contact more gradually to allow players’ brains to adapt so as to reduce the risk of serious injury. This is what the new rules in Illinois, Alabama, Minnesota, and Kansas appear to address. Whether they go far enough is another question.
Prompted by the NFHS Task Force recommendations, member state associations have been reviewing there policies concerning offseason football. In states such as Ohio and Illinois, there were already rules in place to limit contact during the offseason, with teams prevented from participating in full gear or in full-contact practices. Other states that previously had no restrictions in place for offseason football have begun to adhere to the NFHS task force’s guidelines as well.
Cause for concern
Since publication of the first Purdue study, similar findings about the effects of RHI, both in the short- and medium-term, have been reported by researchers (8,9,16,19,21,22,26,27,28, 29-38), with several of the studies finding changes which persisted for weeks and even months after a football season ended.
Summarizing the state of the research in 2015, a study by researchers at the University of Virginia (29) found that, in the short term, RHI has been “linked to increased susceptibility to concussion, decreased cogntitive function, altered gray matter functional connectivity, and changes in white matter microstructure,” and that, in the long term, “retired football players who have sustained high levels of subconcussive impact over their careers have been hypothesized to have an increased risk of developing neurodegenerative disorders, like amytrophic lateral sclerosis [e.g. Lou Gehrig’s disease], Alzheimer’s disease, Parkinson’s disease, and chronic traumatic encephalopathy (CTE).”
An August 2015 editorial in the British Journal of Sports Medicine (41), said that autopsy studies – many conducted in Boston at the Center for the Study of Chronic Traumatic Encephalopathy – and a study reporting that retired NFL players who began playing football before age 12 demonstrated greater levels of cognitive impairment in their 40s-60s than those who started later (40) “raises concern that an accumulation of undiagnosed subconcussive head trauma may lead to (or be a leading factor) for CTE.”
In a 2012 study (8) researchers at the University of Rochester Medical Center (URMC) measured before-and-after data from the brains of a group of nine high school football and hockey players using an advanced form of imaging similar to an MRI called diffusion tensor imaging (DTI). They found subtle evidence of axonal injury at the cellular level in six athletes who had not been diagnosed with concussion but sustained RHI during the normal course of play. The abnormalities disclosed on post-season DTI scans among the players were closer to the scan of the one player with diagnosed concussion than to the normal brains in the control group. Axons, which are like cables woven throughout brain tissue, swell up when traumatic brain injury occurs.
The imaging changes also strongly correlated with the number of head hits (self-reported by the athletes in a diary), the symptoms experienced, and independent cognitive tests, said lead author Jeffrey Bazarian, M.D., M.P.H., associate professor of Emergency Medicine at URMC.
Another 2012 study (19) found that new learning on a sophisticated pencil-and-paper neurocognitive test declined over a single season of RHIs among college football and hockey players who did not experience concussions. The study found that the players had poorer post-season reaction time and scores on a test of visual attention and task switching, which deficits were associated with greater head impact exposures.
Using DTI imaging technique, researchers at Indiana University School of Medicine and the Geisel School of Medicine at Dartmouth College, found in a 2013 study (16) significant differences in brain white matter of varsity football and hockey players compared with a group of non-contact-sport athletes, with the number of times they were hit correlated with changes in the white matter. They also found that some of the athletes, none of whom suffered diagnosed concussions, didn’t do as well as predicted on tests of learning and memory at the end of the season, although the study did not find “large-scale, systemic differences” in the brain scan measures, which the authors found “somewhat reassuring” and consistent with the fact that millions of athletes play contact sports for many years without developing progressive neurodegenerative disorders. ((17,18)
Another 2013 study by researchers at URMC and the Cleveland Clinic (9) also found evidence of brain damage in college football players from RHI in the form of elevated levels of S100B, a protein in the blood usually present only in the brain. The presence of the S100B protein triggers the release by the body of antibodies which can then leak back into the brain through the damaged blood-brain barrier, where they are thought to attack brain tissue. The highest protein levels were found among players who sustained the most hits to the head during games and practices.
Using DTI, researchers at Wake Forest found in a 2014 study (26) that a single season of high school football can produce changes in the white matter of the brain of the type previously associated with mTBI in the absence of a clinical diagnosis of concussion, and that these impact-related changes in the brain are strongly associated with a postseason change in the verbal memory composite score from baseline on the ImPACT neurocognitive test. “Taken together, these data add to the growing body of literature providing evidence that a season of play in a contact sport can show brain changes in the absence of concussion or clinical findings,” they wrote.
In a research paper presented at the annual meeting of the Radiological Society of North America in December 2014 analyzing the same data,(27,28) the Wake Forest researchers found that players experiencing greater levels of RHI (heavy hitters) had more changes to specific areas of their brains compared to players with lower impact exposure (light hitters).
There are also emerging data that football players are more frequently diagnosed with sport-related concussion on days with increased frequency and higher magnitude of head impact (greater than 100g linear acceleration). (43-45)
