How Many Concussions Are Too Many? Measuring the Cumulative Impact on the Brain with Dr. Joseph Maroon | E79

How many concussions are too many—and could we someday measure the cumulative effect of every hit to the head? Dr. Joseph Maroon, longtime team neurosurgeon for the Pittsburgh Steelers and a pioneer in concussion and traumatic brain injury research, joins Life After Impact to discuss multiple concussions, repetitive head impacts, subconcussive exposure, CTE, and the future of concussion testing. 

Dr. Maroon helped develop ImPACT, the neurocognitive test that transformed how the NFL, NHL, and other contact sports evaluate athletes after concussion. Now, his attention has turned to the next major problem in sports concussion research: determining the accumulated burden of head impacts over a lifetime. From sensor-equipped mouthguards that measure impacts in real time to advanced MRI, brain spectroscopy, and research involving former NFL players, Dr. Maroon explains how scientists are moving beyond simply counting concussions toward understanding the actual dose of impact the brain has received.

The question of “How many concussions have you had?” may eventually prove to be far too simplistic.

A player may experience hundreds or thousands of head impacts during years of football, hockey, rugby, MMA, military service, or other high-risk activities without every impact producing a diagnosed concussion.

Dr. Maroon believes concussion research needs something analogous to the “pack-years” physicians use to quantify lifetime cigarette exposure: a way to measure the cumulative dose of repetitive head impacts to the brain.

In this episode, he explains how researchers are getting closer.

One of the most fascinating developments is the use of instrumented mouthguards containing accelerometers. Unlike helmet sensors, the mouthguard is coupled more closely to the skull and can measure the location, magnitude, linear acceleration, and rotational acceleration associated with a head impact.

In rugby, these technologies have already been used to monitor enormous numbers of impacts. Some systems can even produce a visible alert following a sufficiently large impact—essentially creating a neurological version of the “check engine” light.

An alert doesn't diagnose a concussion. Instead, it tells the medical team: this athlete experienced a significant impact and should be evaluated.

But Dr. Maroon is interested in going even further.

Rather than simply measuring the G-force of individual hits, researchers are investigating whether they can calculate the energy transferred during repeated head impacts and accumulate that exposure over time.

Could an athlete eventually have a lifetime “dosimeter” for head impacts—similar to the radiation badges worn by people who work around X-rays?

And could that information help answer one of the hardest questions in sports medicine:

When has a brain had too much?

Dr. Maroon also shares the story behind the development of ImPACT testing. Decades ago, while working with the Pittsburgh Steelers, head coach Chuck Noll challenged him to provide objective evidence for why a concussed quarterback should remain out for a specific period of time.

That challenge helped lead Dr. Maroon and neuropsychologist Dr. Mark Lovell to develop baseline neurocognitive testing, allowing clinicians to measure processing speed, memory, and other cognitive functions before injury and compare them with performance after concussion.

Today, Dr. Maroon sees impact dosimetry as another potential step forward: moving from measuring how the brain performs after an injury toward quantifying what the brain has actually been exposed to.

The conversation extends beyond professional sports. Dr. Maroon discusses research involving Navy Special Warfare Combatant-Craft Crewmen, who can experience thousands of repetitive impacts from high-speed boats slamming against waves, as well as ongoing research involving former NFL and NHL players and other individuals with histories of repetitive head impacts.

He also describes research combining instrumented mouthguards with diffusion tensor imaging (DTI) to investigate whether accumulated impact exposure across a football season corresponds with measurable changes in the brain's white-matter pathways.

Later in the episode, the conversation turns toward what may happen biologically after years of repetitive brain stress—including oxidative stress, mitochondrial dysfunction, neuroinflammation, glutathione depletion, and neurodegeneration.

Dr. Maroon explains his current research using magnetic resonance spectroscopy to measure chemicals such as glutathione directly in the brain and discusses why his team is studying strategies intended to support the brain's antioxidant defenses.

You'll also hear about:

• Multiple concussions and cumulative head-impact exposure
• Pittsburgh Steelers and NFL concussion history
• The origins of ImPACT concussion testing
• Instrumented mouthguards and real-time head-impact monitoring
• Why G-force alone may not tell the whole story
• Linear versus rotational forces on the brain
• Subconcussive impacts in contact sports
• White-matter injury and diffusion tensor imaging
• CTE and long-term brain health
• Repetitive head impacts in military populations
• Glutathione and oxidative stress in the brain
• Mitochondrial health and ATP
• Hyperbaric oxygen therapy and photobiomodulation
• Emerging approaches to measuring and protecting brain health

Perhaps the biggest idea in this conversation is that the future of concussion science may require us to stop thinking about brain injury as a series of isolated events.

The number of diagnosed concussions matters—but the accumulated burden of everything the brain has experienced may matter even more.

Have you had repetitive head impacts? Take part in Dr. Maroons research on glutathione precursors. Email maroonjc@gmail.com