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Do subconcussive hits have the same effect on the brain as clinical concussions?

In January, the Eastern Athletic Trainers Association hosted its annual conference in Philadelphia.  Among the many sports medicine topics presented at this three-day conference was a presentation on subconcussive blows by Ryan Tierney, PhD, ATC; Dianne Langford, PhD; and David Borchardt, MS, ATC.

A subconcussive hit is defined as a head impact that does not result in a clinical concussion.  Generally, a clinical concussion occurs due to a blow to the head, a hard fall, or a sudden change of direction as occurs in a football tackle.  Short-term symptoms of a concussion include headache, dizziness, nausea, short or long-term memory loss, etc.  Some concussions have symptoms that last much longer and have been linked to Alzheimer's, dementia, and CTE (chronic traumatic encephalopathy).

But what about much smaller hits that don't lead to symptoms, are they safe?

Current research is now showing that multiple low-impact hits have many similar effects to the brain as more obvious high-impact hits.

Ryan Tierney, an Athletic Training researcher and expert on concussion at Temple University, presented research showing that numerous subconcussive hits lead to changes between pre and post functional MRIs (F-MRIs) as well as changes in a neuropsychological testing, such as ImPACT1.  Research by Tierney and his colleagues shows repeat head balls from a 25 mph soccer ball — similar to a routine hit to a lineman in a football game — led to subtle changes in the vestibular and ocular-motor systems for up to 48 hours 2,3. Loss or injury to the vestibular system can lead to dizziness or balance issues.

Tierney states, "we now know that the stress on the brain from these low-level impacts can accumulate over time and may lead to problems."  The question now becomes how many subconcussive hits are too many and how should individuals, parents, coaches, and the medical community use this new research in deciding if it is safe for athletes to return to play?

In an interview with Tierney, he told me:

"Hundreds to thousands of head impacts may cause some sports participants to have mild to severe neurological problems later in life.  That's probably not the answer people want, but it's the current state of the science.  One problem is there are a number of factors that can influence how someone responds to head impacts.  Some of these factors include injury history, head impact exposure (e.g., number and magnitude), and genetics. The clinical usefulness of this information, however, is still not completely understood."

In light of this news, the NFL has recently reduced the amount of time a team can participate in contact drills during practice and many colleges have also reduced contact in practice.  USA Soccer has changed rules at the youth level by eliminating head balls in players under the age of 10 and reducing head balls for those aged 10-13.

When asked if rule changes are a good idea, Tierney said, "fewer head impacts are better so rules, playing techniques, and practice activities that involve lowering the number of head impacts are good ideas."

It is important to understand the impact of subconcussive hits and that they can lead to changes similar to concussions, however more research is needed for a conclusive answer.

"Fortunately, due in part to increased awareness, many of these steps are occurring at all levels of sport participation," said Tierney. "Therefore, in the future maybe fewer people will have neurological problems that can be associated with (head injuries from) sports participation."

1)     Talavage T., Nauman E., Breedlove E., Yoruk U., Dye A., Morigaki K., Feuer H., Leverenz L. (2013) Functionally-detected cognitive impairment in high school football players without clinically-diagnosed concussion. J neurotrauma.

2)     Hwang, S., Ma, L., Kawata, K., Tierney, R., Jeka, J. (2016) Vestibular Dysfunction following Sub-Concussive Head Impact. J neurotrauma.

3)     Kawata, K., Tierney, R., Phillips, J., Jeka, J.J. (2016) Effect of Repetitive Sub-concussive Head Impacts on Ocular Near Point of Convergence. Int J Sports Med. 37(5), 405-410.

Read more Sports Doc for Sports Medicine and Fitness.