Science1 publisher3 min readPublished
A high school football season delivers 600 to 1,000 subconcussive blows of unknown consequence
Researchers can say how many head impacts a young football player takes in a season. Nobody has published the cumulative dose at which that exposure becomes dangerous. Parents and schools are deciding without it.
The Scientist · Science desk
What happened
- Data published last month in the BMJ suggests at least one in four former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy, and Nowinski says that figure is an underestimate.
- Other analyses cited by Scientific American put about 40 percent of amateur contact-sport athletes as showing brain changes characteristic of a disease found in under 1 percent of the population.
- The research points at accumulated small impacts, rather than diagnosed concussions, as what drives the disease, so the quantity that needs counting is a player's total head-impact load.
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Why it matters
- constraint Without a dose-response curve, a youth league can only regulate proxies such as minimum age and practice contact; whether a given limit sits above or below the level where harm begins is impossible to check.
- decision A parent deciding at age 10 is weighing a quantified exposure against an unquantified risk. The clinical advice on offer addresses readiness to take a hit, a separate question from how many hits accumulate.
- exposure Concussion counts depend on players reporting symptoms they had reason to hide, so epidemiology built on diagnosed concussions is measuring reporting behaviour as well as injury.
- contradiction Nowinski's prevalence figures and Strelzik's caution describe different populations, and both can hold: high rates among athletes whose brains were studied say little about a child's first four seasons.
A prevalence figure and a dose-response curve are different objects. The numbers in circulation are all prevalence. One in four describes men who played professional football and died between 2016 and 2021 [1]. Set against a general-population rate below 1 percent [4], that is at least 25 times as common [1]. Both are counts of cases, taken without reference to how much football anybody played.
The exposure side is counted. A high school or college player absorbs an estimated 600 to 1,000 subconcussive blows in a single season [6]. Garrit, a 33-year-old former college linebacker who spoke to Scientific American and asked to be identified by his first name, started tackle football at 10 [11]. Apply the per-season figure to every year from age 10 through a final college season, 13 seasons, and the total runs from 7,800 to 13,000 impacts [2]. Youth seasons are presumably lighter than college ones, so the figure is an upper bound. Published research charts that exposure and stops short of the point where risk is known to change.
Millions of amateur athletes play tackle football each year [22]. The clinical guidance their parents get turns on a different variable. Jeffrey Strelzik, an assistant professor of child neurology at Children's National Hospital in Washington, D.C., told Scientific American there is not strong evidence that playing at an early age is bad for you, and that players need to be "developmentally ready" [8]. "Why would we have a small, wobbly five-year-old with poor neck strength tackle?" he said [9]. Neck strength and body size are plausible mediators of how much force reaches the brain on any one hit. Both speak to a single hit; the running total is another matter. Strelzik also said that "any risk needs to be weighed against the benefits of playing team sports" [10].
Counting is harder than the tidy figures suggest. For every diagnosed concussion, college football players sustain about 340 hits harder than the median concussive impact [5]. Diagnoses make up that denominator. A diagnosis generally began with a player raising his hand. "It was on you to self-report, and there was incentive not to because you didn't want to miss playing time," Garrit said [12]. Under-reporting shrinks the denominator and inflates the ratio. Any study that uses diagnosed concussions as its exposure measure is working from a filtered record.
Michael Buckland, the neuropathologist at the University of Sydney who founded the Australian Sports Brain Bank, says the brain has no pain receptors [14]. "If you twist your ankle, it bloody hurts. You don't get that feedback from the brain," he said [15]. The exception comes when damage compromises basic functioning enough to cost consciousness or trigger a seizure [16].
The pathology has been on the record since 1928, when it was described in boxers as "punch drunk" syndrome [21]. Chris Nowinski, a behavioral neuroscientist at Boston University who directs the Concussion Legacy Foundation [19], said "CTE is affecting far more people than anyone wants to accept" [17]. He puts his own odds of having it at 50-50 [18].
What to watch
- A prospective youth cohort pairing instrumented impact counts with later clinical outcomes would be the first design capable of putting a number on the threshold.
- Details of how the BMJ sample of NFL decedents was assembled. How far one in four can be generalised beyond professional players depends on the sampling.
- A youth league that writes its contact limit in impacts per season, rather than by age group, would be acting ahead of the dose evidence.