Subconcussive Hits: The Brain Damage That Happens Without a Concussion Diagnosis

According to research from Virginia Tech’s Head Impact Telemetry System, youth tackle football players average approximately 378 head impacts per season — the vast majority of which fall below the threshold for concussion diagnosis. In high school players, that number climbs higher. In collegiate and professional players, cumulative career impact counts can reach into the tens of thousands.

The question that drives some of the most important research in brain science today is: are these subconcussive impacts truly harmless?

The CTE evidence

The emerging evidence suggests they are not. CTE (chronic traumatic encephalopathy) research from Boston University’s CTE Center — published in JAMA(Mez et al., 2017) — found the pathological condition in 110 of 111 deceased NFL players’ brains examined. Critically, the researchers noted that CTE appears to be driven not only by diagnosed concussions but by the cumulative burden of all repetitive head impacts, including subconcussive ones. A subsequent study by Alosco et al. (2018), also from BU and published in Annals of Neurology, found that the total number of years playing tackle football was a stronger predictor of CTE severity than the number of diagnosed concussions.

What this means for baseline testing

This has transformative implications for baseline testing. If cumulative subconcussive exposure causes progressive brain changes, then serial baseline testing over multiple years might detect those changes before they produce symptoms. An athlete whose annual baseline shows gradually declining processing speed or memory scores — even without any diagnosed concussions — may be showing early effects of repetitive head impact exposure that warrant clinical attention and potentially activity modification.

Accelerometer-equipped mouthguards and helmet sensors are beginning to quantify individual impact exposure throughout seasons, as reported in Frontiers in Bioengineering and Biotechnology (2025). Combined with longitudinal baseline data, this creates a picture of both exposure dose and functional consequence.

Longitudinal baselines matter

At Headquarters, we advocate for longitudinal baseline tracking, especially for athletes in contact and collision sports. A single baseline is valuable. A series of baselines over years — compared against cumulative exposure data — is transformative for long-term brain health monitoring. For related context, see our piece on when to stop playing contact sports.

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