Neuroscience, Biomechanics, and Risks of Concussion in the Developing Brain Over the past 30 years, a number of experimental models of traumatic brain injury TBI have been developed to study various aspects of TBI in humans. This area of research originally focused on adult animal models of moderate to severe brain injuries, and these models have significantly contributed to our understanding of the biomechanics and neurochemical changes that occur after TBI.
Given the frequency of head impacts in contact sports, the public health implications of these consequences may be significant.
The chapter reviews the clinical manifestations, neuroimaging features, risk factors, and animal studies related to repetitive head impacts and multiple concussions. It also discusses the possible long-term neuropathological consequences associated with repetitive head impacts and multiple concussions, including chronic traumatic encephalopathy CTEan emerging diagnostic entity associated with retired athletes with a history of head injury as well with as military personnel exposed to repeated brain injury from blast and other causes.
The goals of this chapter are to provide a comprehensive review of the current literature, to clarify controversies, and to point out important directions for future research.
For example, helmet-based head impact recording devices are typically set to record only impact forces over a minimum threshold e. Although recent advances in technical, statistical, and clinical knowledge have helped to improve research on repetitive head impacts, earlier findings have to be viewed in the context of history: Their importance lies more in their groundbreaking attempts to quantify relevant variables and not necessarily in their specific findings.
Findings from Soccer Studies In soccer, athletes experience repetitive head impacts from using their heads to strike the ball for passing and shooting. Older research involving amateur and professional soccer players indicated an association between cumulative heading and neuropsychological impairments see, for example, Matser et al.
One study of 37 former professional soccer players found mild to severe deficits in the areas of attention, concentration, memory, and judgment in 81 percent of the players. The authors speculated that this finding could be indicative of permanent organic brain damage resulting from repeated traumas from heading the ball Tysvaer and Lochen, In another study involving 53 active professional soccer players, impairments in memory, planning, and visuo-perceptual tasks were observed and compared with those in non-contact-sport athlete controls.
Among the soccer players, performance on these tasks was inversely related to the frequency of heading the ball Matser et al.
Computed tomography scans of 33 former professional soccer players identified central brain atrophy in one-third of study participants, although scans were only visually inspected, and there were no baseline or control comparisons Sortland and Tysvaer, Several other studies, including more recent ones, involving youth soccer players have found no effect of heading on neurocognitive performance Broglio and Guskiewicz, ; Guskiewicz et al.
Furthermore, studies that have directly assessed changes in cognition related to heading a soccer ball have failed to establish any relationship between heading and neurocognitive changes.
Following detailed observation of heading frequencies by 63 high school soccer players and the administration of Immediate Post-Concussion Assessment and Cognitive Testing ImPACTKontos and colleagues found no differences in neurocognitive performance or symptoms among low- moderate- and high-exposure header groups.
Similarly, Putukian and colleagues found no changes in neuropsychological test scores between pairs of collegiate soccer players who headed the ball in practice for 20 minutes compared with those who did not head in practice.
Kaminski and colleagues conducted two studies with 71 and female collegiate soccer players. Using heading counts as the independent variable and pre- and post-season balance and neuropsychological tests to determine neuropsychological changes, they found no significant relationships on any test measure.
Early research using magnetic resonance imaging MRI and cognitive tests found no significant cognitive impairments or differences on MRI scans among soccer players, boxers, and track and field athletes Haglund and Ericksson, In a recent study using diffusion tensor imaging DTI scans on 12 German soccer players and 11 swimmers, several group differences in brain white matter were noted, including increased radial diffusivity and axial diffusivity in soccer players compared to swimmers Koerte et al.
Although the authors of the study suggest that heading in soccer may lead to neurophysiological changes in the brain, this study's generalizability is limited because of the small number of participants and because it did not include a baseline scan. Furthermore, it is not clear what the functional significance of such findings would be.
In summary, studies of the consequences of heading in soccer have obtained mixed results, with more recent studies showing no relationship between heading and neuropsychological impairment.
The positive findings of some older studies may have been due in part to the more frequent use in the s and s 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 Smodlaka, Today, players use waterproof synthetic soccer balls that absorb less water Kirkendall and Garrett, The DTI study Koerte et al.
Due to small sample sizes and other methodological limitations, caution is required in interpretation of these studies' findings.
Findings from Football and Ice Hockey Studies As is the case with soccer players, football and ice hockey players can incur repetitive head impacts Brainard et al. For example, a lineman in football who tackles another player with his head in successive plays experiences a series of repetitive head impacts.
Hockey players may experience repetitive head impacts from collisions with the board and with other players. McAllister and colleagues examined repetitive head impacts over a single season in collegiate football and ice hockey athletes and compared those athletes with a group of athletes who played a non-contact sport on a variety of measures.
A subset from one of the three Division I universities also completed a paper-and-pencil neuropsychological battery and had preseason and postseason neuroimaging. There were no group differences on cognitive tasks over a sport season.
The researchers also examined baseline neurocognitive tests scores across three sport seasons and found no differences on baseline assessments among the sport groups, suggesting that previous exposures to contact did not affect test scores negatively.
However, the researchers did report that a higher percentage of the contact sport athletes performed worse than those in the non-contact group on a measure of new learning California Verbal Learning Testwith no ImPACT composites showing significant change.
Furthermore, the authors found that impact exposure above the 95th percentile in frequency during the last week of the season was related to poorer performance on the Trail Making test, a measure of visual attention and task switching, and that the peak linear acceleration for the season was related to slower ImPACT reaction times.
A relationship among recent biomechanical exposures, brain white matter integrity, and lower scores was also found, although the absolute value of significant test score decline did not reach impairment level.
Other studies of the effects of repetitive head impacts in high school and collegiate football players have found no association with neurocognitive impairment or physiological changes see, for example, Broglio et al. However, these studies all have methodological weaknesses.
Only McAllister and colleagues used non-contact controls and adjusted neurocognitive test scores for practice effects, baseline levels, regression to the mean, and relevant demographic factors, while also comparing seasonal exposure and recent exposures across biomechanical measurements of magnitude and frequency.
A few small studies of high school and collegiate football and hockey players have looked at DTI, neurocognitive test scores, and biomechanical data; these have found axonal changes but mixed neuropsychological findings Bazarian et al.
Evidence for the effects of repetitive head impacts on diffuse axonal injury in humans comes largely from DTI studies that measure directionality fractional anisotropy, or FA and regularity mean diffusivity, or MD of white matter tracts.Objectives There has been increased interest in sports-related concussions from the professional level down to youth leagues in recent years.
Symptom types and resolution time are the metrics most. Injury Definition: Sports concussion Youth have a more prolonged recovery and are more susceptible to concussions. Sport, position and style of play. Repeated concussions occurring with progressively less impact force or slower recovery after each successive concussion.
Age. Concussion is defined as a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces. Several common features that incorporate clinical, pathologic and biomechanical injury constructs that may be utilized in defining the nature of .
Sports-Related Concussions in Youth: Improving the Understanding the biomechanics of sports-related concussions in youth requires knowledge about what head and neck movements and applied forces occur in an array of sporting environments, how the developing head and neck mechanical and biological properties change with age and gender, how.
Studies of Repetitive Head Impacts. As with much of the clinical literature on the consequences of concussions in sports, the generalizability of many studies of the effects of repetitive head impacts is limited by methodological weaknesses.
Participation in youth sports and sports-related activities has risen dramatically over the past several decades, given the increased number of programs for both male and female youths.
Furthermore, the recognized benefits of physical fitness resulted in more adolescent involvement in competitive sports.