The severity of injury associated with sport concussions that present with a loss of consciousness or impact seizures is ambiguous. A disconnect between the clinical and biomechanical aspect can be observed throughout the literature pertaining to loss of consciousness and impact seizures. Clinicians have dismissed a loss of consciousness or the presence of impact seizures as an indicator of severity. However, early biomechanical research suggests that loss of consciousness is caused by greater magnitudes of impacts and damage to more vulnerable brain regions. However, this research was conducted on animal and cadaver models and may not adequately represent sport-related concussions. Recent methodologies such as laboratory reconstructions of head impacts and finite element modeling can provide new information on the severity of impact associated with these signs of concussions. Study One compared the magnitudes of head dynamic response and brain tissue deformation between impact representations of punches that lead or do not lead to LOC in boxing. The main findings of this study revealed knockout punches were the result of by unprotected hooks to the mandibular angle resulting in greater brain tissue trauma. Study Two compared cases of concussions with and without LOC in American football. Head dynamic response and brain tissue deformation was also greater in the LOC group in this sport, consistent with boxing impacts. The main predictor of LOC was found to be impact velocity which has implications in terms of prevention. Study Three compared the magnitudes of head dynamic response and brain tissue deformation between cases of concussions with a loss of consciousness and cases of concussion with impact seizures in American football. The two types of clinical presentations had similar severities of brain tissue deformation with the exception of strain rate in the white matter being smaller in cases of impact seizures. The findings of this thesis support the notion that concussions with loss of consciousness or impact seizure represent a more severe injury than concussions without these signs. It may be appropriate to address these signs of injury differently in return to sport protocols to reflect their severity. The findings also suggests that prevention of loss of consciousness should be sport specific. Hooks to the side of the jaw were the primary cause in boxing, whereas LOC could be caused by different event types in American football. However, in both sports, impact velocity and impact location played an important role in the risk for loss of consciousness.

Falls and collisions are the most common types of events leading to sports-related concussions where impacts to the head play an important role on the onset of traumatic brain injury. Each event can be described by impact parameters that define the loading conditions on the head and brain and are necessary for accurate accident reconstruction employing physical impact tests, anthropometric headforms, and finite element (FE) modelling. It was the purpose of this research to describe the effects and interactions of impact velocity, compliance, mass and impact location on head acceleration and brain tissue strain measures associated with risk of concussions in sports. Impact parameters were varied to capture responses from no-injury up to concussive levels. Study one examined the effect of impact parameters on fall events simulated using a monorail drop tower. Impact mass was varied using three different headforms representing child, adolescent, and adult sizes measuring peak linear and angular acceleration and maximum principal strain. Regression analysis revealed that impact compliance was the most influential on peak linear and angular acceleration measures, meanwhile FE strain was most affected by changes in impact velocity. Smaller headforms tend to produce higher acceleration and strain values, supporting the need for age and size related mechanical definitions of risk. Study two examined the effect of impact parameters for collision events simulated using a multi-mass pendulum to represent common striking masses in sport measuring peak linear and angular acceleration and strain. Study three provided further insight into collision impacts by evaluating the distribution of peak strains in different brain lobes and the volume of the brain experiencing strains passed a critical level. Results show that compliance was similarly the most influential on peak head acceleration whereas peak strain and volume were most affected by impact velocity. Mass-velocity interactions had effects where a 9 kg mass had greater response than 15 kg, but similar to 21 kg. The temporal lobe consistently contained the highest strains with the rear boss non-centric impact location producing the largest values. Interacting impact parameters illustrate the challenges with predicting associated risk of concussion from head collisions in sport and supports the need to identify effective performance ranges of protective materials.

The primary purpose of this study was to determine the association between Apolipoprotein E (APOE) genotype and head impact response in high school athletes. The secondary purpose was to determine if quality of life (QoL) and cognitive functioning scores significantly differ between Apolipoprotein (APOE) rare allele carriers versus non-carriers within a poor head impact response (PHIR) group of high school athletes. Thirty (28 males, 2 females) high school athletes playing high head impact sports participated in the study. A between-subjects design was used. Primary aim one independent variable was genotype (i.e., APOE E4 carriers vs. non-carriers and APOE G-219T carriers vs. non-carriers) and dependent variable was group [i.e., normal head impact response (NHIR) vs. PHIR]. Statistical analysis consisted of Fisher's exact tests. Alpha level was set at p p p = .002) in the overall QoL scores between APOE G-219T promoter rare allele carriers versus non-carriers within the PHIR group. No other statistically significant differences were found; however, there was a trend (p = .007) found in the psychosocial subscores in the APOE G-219T promoter rare allele carriers versus non-carriers within the PHIR group. Carrying an APOE rare G-219T rare allele was associated with significantly lower QoL scores within the PHIR group, these results indicate that athletes with intrinsic (e.g., genotype) risk factors may need more education and different treatment following head impacts. / Kinesiology

Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury. / Master of Science / Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury.

Chronic Traumatic Encephalopathy (CTE) is a neurodegenerative disease that is associated with repetitive traumatic brain injury like those sustained in sport, military combat, and other activities with repetitive head impact exposure. Repetitive head impacts typically cause mild traumatic brain injury (mTBI) resulting in both concussive and subconcussive injury. Repeated mTBIs injuries appear to cause an abnormal accumulation of proteins, including hyperphosphorylated tau (p-tau) and TDP-43, progressive axonal failure with gradual structural degradation, microvascular disruption, breach of blood-brain barrier, neuroinflammation and microglial activation; each of these manifestations lead to axonal degeneration and neuronal death, which impairs neuronal pathways and are likely to give rise to CTE symptoms. CTE can be microscopically characterized mainly by p-tau accumulation in perivascular spaces and at the depths of the cortical sulci. Clinical presentation of CTE may include behavioral, mood, cognitive, or motor symptoms. Some of the common symptoms include impulsivity, aggression, anxiety, depression, memory impairment, dementia, and suicidality. The Locus Coeruleus (LC), a nucleus in the pons of the brainstem, is suspected to be involved in CTE. The LC provides the main source of norepinephrine to the entire brain and is critical for its control over arousal, behaviors, attention, and memory. Dysfunction of the locus coeruleus has shown to cause a wide array of symptoms, many of which are similar to those seen in CTE. Furthermore, the LC is affected in many other neurodegenerative diseases and is believed to be responsible for the progressive and widespread nature of the various diseases and their clinical symptoms. Although the LC has been implicated in CTE there have been no studies examining LC pathology in relation to the disease progression or its symptoms. We hypothesize LC CTE pathology should increase with the severity of CTE. Furthermore, increased CTE pathology in the LC should create disturbances to the LC and the LC-NE system and manifest clinically. Specifically, LC CTE pathology may be associated with age of onset of general behavioral and cognitive symptoms as well as individual symptoms and outcomes including impulsivity, depression, depressed mood and death by suicide. To determine this, a postmortem study was performed on 184 individuals with a history of RHI and no comorbid diseases examining the relationship between AT8-immunopositive tau density in the LC and various clinical variables. The study found that LC AT8 density showed a significant positive correlation with duration of repetitive head impact (RHI) exposure when controlled for age. There also was a significant increase in LC AT8-immunoreactive tau in cases with stage III and IV CTE compared to those with no CTE and stage I and II CTE, and AT8 density was predictive of CTE stage when controlled for age. There were no significant relationships found between density of LC AT8-immunoreactive tau and age of any CTE symptom onset or individual symptom (impulsivity, depressed mood, MDD, death by suicide) presence. Future studies should continue to evaluate CTE pathology in the LC and its effects on both the pathological and clinical characteristics of the disease.

The objective of this research was to better understand how impact angle influences headform dynamic response and brain tissue deformation. A bare headform was impacted using a pneumatic linear impactor at 5.5 m/s. The impacts were directed on the front and side location at angles of 0, 5, 10 and 15° rightward rotations as well as -5, -10 and -15° (leftward) rotations at the side to examine the characteristics of the head and neckform on the results. Peak resultant linear and rotational accelerations from the headform as well as peak maximum principal strain (MPS) and von Mises stress (VMS) estimated from a brain finite element model were used to measure the effect of impact angle. Significant results were dependent upon the impact angle and location as well as the dependent variable used for comparison (p <0.05). Impact angle produced significant differences in rotational acceleration and MPS at both the front and side; however angle only had an effect on VMS and linear acceleration at the front and side locations, respectively. These findings show that the effect of impact angle is asymmetrical and is specific to the dependent variable. This study suggests that varying impact angle alone may not be as influential on headform dynamic response and brain tissue deformation and that the severity of an impact may be more of a function of how both location and angle create high risk conditions.

The objective of this research was to better understand how impact angle influences headform dynamic response and brain tissue deformation. A bare headform was impacted using a pneumatic linear impactor at 5.5 m/s. The impacts were directed on the front and side location at angles of 0, 5, 10 and 15° rightward rotations as well as -5, -10 and -15° (leftward) rotations at the side to examine the characteristics of the head and neckform on the results. Peak resultant linear and rotational accelerations from the headform as well as peak maximum principal strain (MPS) and von Mises stress (VMS) estimated from a brain finite element model were used to measure the effect of impact angle. Significant results were dependent upon the impact angle and location as well as the dependent variable used for comparison (p <0.05). Impact angle produced significant differences in rotational acceleration and MPS at both the front and side; however angle only had an effect on VMS and linear acceleration at the front and side locations, respectively. These findings show that the effect of impact angle is asymmetrical and is specific to the dependent variable. This study suggests that varying impact angle alone may not be as influential on headform dynamic response and brain tissue deformation and that the severity of an impact may be more of a function of how both location and angle create high risk conditions.

The primary goal of the American football helmet has been protection of players against skull fractures and other traumatic brain injuries (TBI) [Cantu 2003, Benson 2009]. TBI can result from short, high magnitude linear impact events typical of when the head impacts a hard surface [Gilcrhist 2003, Doorly 2007]. The modern helmet, which has evolved and become well designed to mitigate TBI injuries, does not offer sufficient protection against injury such as concussion, and the incident rate remains high in sport [Broglio 2009, Rowson 2012]. Researchers speculate rotation of the head leads to shear strain on the brain tissue, which may be the underlying mechanism of injury leading to concussive type injuries [Gennarelli 1971, Ommaya 1974, Gennarelli 1982, Prange 2002, Gilcrhist 2003, Aare 2003, Zhang 2004, Takhounts 2008, Greenwald 2008, Meaney 2011]. This has led researchers to investigate new liner materials and technologies to improve helmet performance and include concussive injury risk protection by attempting to address rotational acceleration of the brain [Mills 2003, Benson 2009, Caserta 2011, Caccese 2013]. To improve current football helmet designs, technology must be shown to reduce the motion of the brain, resulting in lower magnitudes of dynamic response thus reducing maximum principal strain and the corresponding risk of injury [Margulies 1992, Zhang 2004, Mills 2003, Kleiven 2007, Yoganandan 2008 Caserta 2011, McAllister 2012, Caccese 2013, Post 2013, Fowler 2015, Post 2015a/b]. Recent research has studied the use of decoupling liner systems in addition to the existing liner technology, to address resultant rotational acceleration. However, none of this previous work has evaluated the results in terms of the relationship between brain motion, tissue strain, and injury risk reduction. This thesis hypothesises the use of decoupling strategies to reduce the dominant coordinate component of acceleration in order to decrease maximum principal strain values. The dominant component of acceleration, defined as the coordinate component with the highest contribution to the resultant acceleration for each impact, is a targetable design parameter for helmet innovation. The objective of this thesis was to demonstrate the effect liner strategies to reduce the dominant component of rotational acceleration to decrease maximum principal strain in American football helmets.

The objective of this research was to better understand how impact angle influences headform dynamic response and brain tissue deformation. A bare headform was impacted using a pneumatic linear impactor at 5.5 m/s. The impacts were directed on the front and side location at angles of 0, 5, 10 and 15° rightward rotations as well as -5, -10 and -15° (leftward) rotations at the side to examine the characteristics of the head and neckform on the results. Peak resultant linear and rotational accelerations from the headform as well as peak maximum principal strain (MPS) and von Mises stress (VMS) estimated from a brain finite element model were used to measure the effect of impact angle. Significant results were dependent upon the impact angle and location as well as the dependent variable used for comparison (p <0.05). Impact angle produced significant differences in rotational acceleration and MPS at both the front and side; however angle only had an effect on VMS and linear acceleration at the front and side locations, respectively. These findings show that the effect of impact angle is asymmetrical and is specific to the dependent variable. This study suggests that varying impact angle alone may not be as influential on headform dynamic response and brain tissue deformation and that the severity of an impact may be more of a function of how both location and angle create high risk conditions.

The incidence of concussive injury has continued to arise annually with up to 3.8 million concussions reported per year (Thurman 1999) and 15% of these injuries occurring with persistent symptoms (Kraus and Chu, 2005). Few studies have examined the differences between youth and adult concussion (Yeates et al, 2012; Gosselin et al, 2010) therefore it is unknown whether youth and adults pose a similar risk of sustaining a concussion following impact. For this reason, the purpose of this study is to determine if differences exist in the dynamic response of the head and brain tissue deformation characteristics between children and adolescents for falls in comparison to adult data which have resulted in concussive injuries. Patient data was collected from emergency room hospitals across Canada. After exclusion criterion was applied, 11 child and 10 adolescent falls were reconstructed using mathematical (MADYMO) model, physical model (Hybrid III Headforms) and finite element modelling. Both groups were compared to each other as well as an adult group collected by Post et al (2014b) using a one-way ANOVA and Welsh test. The results of this study show that the children produced the lowest values for all variables when compared to the adolescents and adults whereas the adolescents produced the largest (with the exception of MPS where the adolescent and adult MPS was the same). Although all results were above the suggested thresholds for risk of concussive injury, the youth produced the lowest brain tissue strain yet still suffered a concussion. This is important to note as it may suggest that children are at an increased risk of injury at a lower brain tissue strain level. Understanding the differences in parameters influencing concussive injury may aid researchers in comprehending the unique risk for youth at difference ages. This information would be useful in terms of protective equipment design, promoting safe play in games and management of patients following injury.