Hidden Toll of Head Impacts on Brain Health

In recent years, the scientific community has made significant strides in understanding the long-term consequences of repetitive head impacts (RHI), shedding light on the silent but serious damage that accumulates with each jolt to the brain. 

Every hit matters?

Mounting evidence now shows that it’s not just concussions that raise concern—it’s also the total volume and intensity of head acceleration over time that correlates with chronic neurological side effects.  A seminal study led by Montenigro et al. (2017) introduced the Cumulative Head Impact Index (CHII), a metric derived from helmet accelerometer data that estimates an athlete’s lifetime exposure to head impact forces  based on position and play history. Their findings were striking: once an individual crossed a certain threshold of cumulative impact exposure, their risk for developing depression, executive dysfunction, apathy, and objective cognitive impairments rose. Of particular interest, this elevated risk was more closely tied to CHII than to any individual metric like total years played or even reported concussions. In other words, total head trauma sustained, regardless of whether symptoms were present or not, was a better of later life outcomes than simply looking at concussion history or years of football experience alone.

More recently, Daneshvar et al. (2023) built upon this work using an advanced Position Exposure Matrix, again derived from helmet accelerometer data. Their research on over 600 former football players showed that models incorporating these acceleration-based metrics outperformed traditional metrics in predicting the presence and severity of chronic traumatic encephalopathy (CTE), a degenerative brain condition. Notably, informant-reported concussions and even player position alone were not as reliably associated with CTE pathology. Instead, the best predictors were cumulative g-force and rotational acceleration—forces that occur even in so-called "routine" plays (Daneshvar et al., 2023).

Together, these studies underscore a growing scientific consensus: accumulated biomechanical load to the brain—not just diagnosed concussions—is a primary driver of long-term neurodegenerative and cognitive outcomes. This has profound implications for how we assess risk in contact sports, develop protective equipment, and set guidelines for safe play. It also challenges long-held assumptions, urging a shift from focusing solely on symptomatic events to managing cumulative exposure to all head impacts.

What next?

For parents, coaches, and athletes: becoming more aware of what activities result in any head impacts and reconsidering whether that activity is absolutely necessary or can be modified to reduce head impact exposure.  As researchers refine these exposure metrics and develop better real-time monitoring tools, the path forward becomes clearer: prevention and early intervention must be guided not just by symptoms, but by science-backed management of biomechanical loading to the head of every athlete.