Multiple concussion effects
The committee examined data on the effects of single and multiple concussions and found some observed impairments in the areas of memory and processing speed. It also determined that a history of previous concussions is a predictor of increased risk for future concussions, although the extent to which the risk is increased is unknown. In several studies,[6,7] the number and severity of concussion symptoms is greater in athletes with a history of two or more concussions. Additionally, athletes with a history of prior concussions may have more severe subsequent concussions[7] and may take longer to recover.[8,9] The time interval between concussions may also be an important factor in the risk for and the severity of subsequent concussions.[10].
Surveys of retired professional athletes, the report said, provided some evidence that a history of multiple concussions increases risk for depression. Noting that very little research has evaluated the relationship between concussions and suicidal thoughts and behaviors, the report there was currently "no data to evaluate this relationship because existing post-concussion symptom evaluations do not assess suicidal thoughts."
Consistent with the view of most concussion experts, the committee also concluded that whether repetitive head impacts and multiple concussions sustained in youth lead to long-term neurodegenerative disease, such as Chronic Traumatic Encephalopathy (CTE), remains unclear, thus pouring cold water on the prevailing media narrative, which has largely taken as a given the existence of such a causal link as a scientific fact.
Soccer heading: no evidence of effect on neurocognitive function
The report found that studies of the consequences of heading in soccer have obtained mixed results, with more recent studies showing no relationship between heading and neuropsychological impairment. It attributed the positive findings of some older studies to being due in part to the more frequent use in the 1980s and 1990s of soccer balls that absorbed more water, increasing the weight of the ball by up to 20 percent and potentially making them more dangerous for heading. Today, players use waterproof, synthetic soccer balls that absorb less water.
Limits on full contact practices: no agreement
While noting the movement towards limiting full contact practices at various levels of football, the report found that support for such limits was "not universal. Some believe that the technology to quantify the number and magnitude of head impacts is not adequately developed and that the science behind setting a specific threshold is not well defined."
Furthermore, the committee noted that :there is some concern that delaying or reducing contact in practice puts athletes at risk down the road as they have not adequately learned appropriate contact skills at an early age when the ability to acquire skills is at its greatest, pointing to recommendations by researchers, including Kevin Guskiewicz, advocating for proper coaching techniques that emphasize fundamentals and the development and enforcement of sport-specific rules to prevent unsafe behavior and to reduce but not eliminate contact.
No scientific basis for 'hit counts'
While the report recognized that several organizations had called for a "hit count" in youth sports to limit the amount of head contact a particular player should experience over a given amount of time, and that "the concept of limiting the number of head impacts is fundamentally sound," the committee found that implementing a specific threshold for the number of impacts or the magnitude of impacts per week or per season was without scientific basis.
Buyer beware
The report expressed concerns that "the makers of sports protective
equipment have taken advantage of growing concussion awareness by making
unsubstantiated claims that certain products can reduce concussion
risk." It warned that, "in order to avoid a false sense of security, it
is important that athletes, parents, and coaches be aware of—and that
marketers of sports equipment
accurately convey—the limitations of protective equipment as it relates to concussions."
Until a universally accepted injury risk curve for concussions is established, as well as associated variants with age and perhaps direction, "claims of reduced concussion risk with protective devices will not be based on fundamentally sound science."
Creating safe concussion reporting environment urged
The committee was encouraged by studies finding that greater athlete knowledge about concussions and more favorable attitude toward reporting possible concussion was associated with increased reporting prevalence of concussion and "bell-ringer" events in these youth." [11,12,13] At the same time, it recognized that "reporting intention may not always be an indicator of what an individual's actual concussion reporting behaviors will be," pointing to several recent studies[11,12,13] that "suggest that future concussion education initiatives should focus on improving attitudes and beliefs about concussions among athletes, coaches, and parents."
Limited research on youth
Although the committee that wrote the report examined useful scientific information to inform its study, it discovered that research about youth concussions was limited. To address these gaps in knowledge, the committee identified several areas for further research, including establishing a national surveillance system to accurately determine the number of sports-related concussions, identifying changes in the brain following concussions in youth, conducting studies to assess the consequences and effects of concussions over a life span, and evaluating the effectiveness of sports rules and playing practices in reducing concussions.
"The findings of our report justify the concerns about sports concussions in young people," said Robert Graham, chair of the committee and director of the national program office for Aligning Forces for Quality at George Washington University, Washington, D.C. "However, there are numerous areas in which we need more and better data. Until we have that information, we urge parents, schools, athletic departments, and the public to examine carefully what we do know, as with any decision regarding risk, so they can make more informed decisions about young athletes playing sports."
Report sponsors
The report was sponsored by Centers for Disease Control and Prevention, U.S. Department of Defense, U.S. Department of Education, Health Resources and Services Administration, National Athletic Trainers' Association Research and Education Foundation, the National Institutes of Health, and the CDC Foundation with support from the National Football League. The Institute of Medicine and the National Research Council are part of the National Academy of Sciences, a private, nonprofit institution that provides independent, evidence-based advice under an 1863 congressional charter. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies.
1. Institute of Medicine (IOM) and National Research Council (NRC). 2013. Sports-related concussions in youth: Improving the science, changing the culture. Washington, DC: The National Academies Press.
2. McCory P, et al. Consensus Statement on Concussion in Sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012. Br. J. Sports Med. 2013:47:250-258.
3. Harmon K, et al. American Medical Society for Sports Medicine position statement: concussion in sport. Br J Sports Med. 2013;47:15-26.
4. Echemendia R, Bruce J, Bailey C, Sanders J, Arnett P, Vargas G. The Utility of Post-Concussion Neuropsychological Data in Identifying Cognitive Change Following Sports-Related MTBI in the Absence of Baseline Data. Clin Neuropsy 2012;26(7):1077-1091.
5. Schmidt J, Register-Mihalik J, Mihalik J, Kerr Z, Guskiewicz K. Identifying Impairments after Concussion: Normative Data vesus Individualized Baselines. Med & Sci Sports & Exer. 2012;44(9):1621-1628.
6. Brooks BL, McKay CD, Mrazik M, Barlow KM, Meeuwisse WH, Emery CA. Subjective, but not Objective, Lingering Effects of Multiple Past Concussions in Adolescents. J Neurotrauma 2013;30:1469-1475.
7. Schatz P, Moser RS, Covassin T, Karpf R. Early Indicators of Enduring Symptoms in High School Athletes with Multiple Previous Concussions. Neurosurgery 2011;68:1562-1567.
8. Colvin AC, Mullen J, Lovell MR, West RV, Collins MW, Groh M. The Role of Concussion History and Gender in Recovery from Soccer-Related Concussion. Am. J. Sports Med. 2009; 37(9): 1699-1704.
9. Castile L, Collins CL, McIlvain NM, Comstock RD. The epidemiology of new versus recurrent sports concussions among high school athletes, 2005-2010. Br. J. Sports Med 2012; 46:603-610.
10. Eisenberg M, Andrea J, Meehan W, Mannix R. Time Interval Between Concussions and Symptom Duration. Pediatrics 2013;132(1):1-10.
11. Register-Mihalik JK, Guskiewicz KM, Valovich McLeod TC, Linnan LA, Meuller FO, Marshall SW. Knowledge, Attitude, and Concussion-Reporting Behaviors Among High School Athletes: A Preliminary Study. J Ath Tr. 2013;48(3):000-000. DOI:10.4085/1062-6050-48.3.20 (published online ahead of print)
12. Chrisman SP, Rivara FP, Schiff MA, Zhou C, Comstock R.D. Risk factors for concussive symptoms 1 week or longer in high school athletes. Brain Injury 2013;27(1):1-9.
13. Register-Mihalik JK, Linnan LA, Marshall SW, Valovich McLeod TC, Mueller FO, Guskiewicz KM. Using theory to understand high school aged athletes' intentions to report sport-related concussion: Implications for concussion education initiatives. Brain Injury 2013;27(7-8):878-886.
Posted October 30, 2013, most recently updated and revised November 1, 2013
