The sternocleidomastoid (SCM) and upper trapezius (UT) muscles are the primary dynamic stabilizers of the head and neck and likely attenuate head acceleration with direct and indirect impacts. Increasing the strength of the SCM and UT through cervical resistance training has been recommended to prevent concussions in football players. The purpose of this study was to examine the effects of an eight-week isoinertial cervical resistance training program on SCM and UT muscle activity (EMG) and kinematic responses of the head and neck during a standard football tackle in college-aged males. Sixteen college-aged males (21.6 ± 2.8 y, 94.6 ± 13.3 kg) with previous high school football or rugby playing experience completed an eight-week isoinertial cervical resistance training program consisting of three sets of 10 repetitions of neck extension, flexion, right and left lateral flexion at 60-80% of 10 repetition maximum two to three times a week. Isometric cervical strength, neck girth, EMG, and kinematic responses of the head and neck during a standard football tackle were measured before and after training. All kinematic data were gathered using a three-dimensional motion capturing system. Training resulted in 7 and 10% increases in isometric cervical extension and left lateral flexion strength, respectively, but no changes were seen in isometric flexion or right lateral flexion strength or neck girth. Additionally, training had no influence on the EMG responses of the SCM or UT, peak linear (7.23 vs. 7.59 g, p = 0.115; pre- vs. post-training) or angular (431.96 vs. 452.37 rad/s2, p = 0.864) head accelerations during the standard football tackle. The UT demonstrated approximately 40% higher absolute EMG activity than the SCM during tackling both before and after training. Under the current experimental conditions, despite modest increases in isometric cervical extension and left lateral flexion strength, the eight-week isoinertial cervical resistance training program failed to augment dynamic stabilization of the head and neck during a standard football tackle in college-aged males. Future research should examine the effects of both slow speed load-intensive and high speed low-to-moderate load intensity isoinertial training as well as plyometric training in decreasing head acceleration during football tackling for injury prevention purposes.

The goals of this study were to measure the ability of catcher's masks to attenuate head accelerations upon impact with a baseball, and to compare these head accelerations to established injury thresholds for concussions. Testing involved using a pneumatic cannon to shoot baseballs at an instrumented (3-2-2-2 accelerometer array) Hybrid III headform (a 50th percentile male head and neck) with and without a catcher's mask on the head. The ball speed was controlled from approximately 26.8 – 35.8 m/s (60 – 80 mph) and regulation NCAA baseballs were used. Peak linear resultant acceleration was 140 – 180 g without a mask and 16 – 30 g with a mask over the range of balls speeds investigated. Peak angular resultant acceleration was 19500 – 25700 rad/sec2 without a mask and 2250 – 3230 rad/sec2 with a mask. The Head Injury Criterion was 93 – 181 without a mask and 3 – 13 with a mask and the Severity index was 110 – 210 without a mask and 3 – 15 with a mask. Catcher's masks reduced head acceleration metrics by approximately 85% when baseballs were impacted with just the headform. Head accelerations with a catcher's mask were substantially lower than contemporary injury thresholds, yet evidence indicates that baseball impacts to the mask still result in concussions. / Master of Science

The studies presented in this dissertation investigated biomechanical factors associated with sports-related brain injuries on the field and in the laboratory. In the first study, head impact exposure in youth football was observed using a helmet mounted accelerometer system to measure head kinematics. The results suggest that restriction on contact in practice at the youth level can translate into reduced head impact exposure over the course of a season. A second study investigated the effect of measurement error in the head impact kinematic data collected by the helmet mounted system have on subsequent analyses. The objective of this study was to characterize the propagation of random measurement error through data analyses by quantifying descriptive statistic uncertainties and biases for biomechanical datasets with random measurement error. For distribution analyses, uncertainties tend to decrease as sample sizes grow such that for a typical player, the uncertainties would be around 5% for peak linear acceleration and 10% for peak angular (rotational) acceleration. The third and fourth studies looked at comparisons between two headforms commonly used in athletic helmet testing, the Hybrid III and NOCSAE headforms. One study compared the headform shape, particularly looking at regions that are likely to affect helmet fit. Major differences were found at the nape of the neck and in the check/jaw regions that may contribute to difficulty with fitting a helmet to the Hybrid III headform. For the final study, the impact responses of the two headforms were compared. Both headforms were mounted on a Hybrid III neck and impacted at various magnitudes and locations that are representative of impacts observed on the football field. Some condition-specific differences in kinematic parameters were found between the two headforms though they tended to be small. Both headforms showed reasonable repeatability. / Ph. D.

As many as 3.8 million sports-related traumatic brain injuries (TBIs) occur each year, nearly all of which are mild or concussive. These injuries are especially concerning given recent evidence that repeated concussions can lead to long-term neurodegenerative processes. One way of reducing the number of injuries is through improvements in protective equipment design. Safety standards and relative performance ratings have led to advancements in helmet design that have reduced severe injuries and fatalities in sports as well as concussive injuries. These standards and evaluation methods frequently use laboratory methods and brain injury criteria that have been developed through decades of research dedicated to determining the human tolerance to brain injury. It is necessary to determine which methods are the most appropriate for evaluating the performance of helmets and other protective equipment. Therefore, the aims of this research were to evaluate the use of different brain injury criteria and apply them to laboratory evaluation of helmets. These aims were achieved through evaluating the predictive capability of different brain injury criteria and comparing laboratory impact systems commonly used to evaluate helmet performance. Laboratory methods were developed to evaluate the relative performance of hockey helmets given the high rate of concussions associated with the sport. The implementation of these methods provided previously unavailable data on the relative risk of concussion associated with different hockey helmet models. / Ph. D.

The research presented herein is a combination of work done in two distinct subcategories of sport related head injury research. The body of work is aimed at increasing the understanding of head impact biomechanics across a broad spectrum of impact scenarios as well as the ability of helmets to affect head impact biomechanics over time. The first study utilizes in situ testing of controlled impacts of an instrumented head form to more fully characterize head accelerations resulting from impacts to the ice, board, and glass surfaces present in an ice hockey rink. The full characterization of head impacts across a spectrum of loading conditions and impact surfaces gives researchers insight into head impact tolerance and head protection capabilities and limitations in ice hockey. The second study details the development of a method to impact helmet pads for repeated loading studies based on published head impact exposure data. The third study uses this newly developed methodology to test the effects of a season of impacts on the energy absorbing properties of three different helmet padding technologies. The body of work is aimed at increasing understanding of head impact and concussion and the ability of existing helmet technologies to prevent these injuries with a goal of reducing the occurrence of injury. / Master of Science

<div>Since the discovery of chronic traumatic encephalopathy (CTE) in retired professional football players, the long-term neurological safety of these athletes has been called into</div><div>question. Studies revealed that those who play football are at higher risk for developing neurological deficits such as Parkinson’s and Alzheimer’s diseases. It has also been observed that participation in contact sports can result in neurological changes detectable with magnetic resonance imaging (MRI) that do not present with any easily observable clinical symptoms. Changes in brain chemistry, structure, and blood flow have been observed over the course of a season of contact sports. These changes are thought to be caused by the repetitive head acceleration events (HAEs) sustained by contact sport athletes, with the magnitude and number of HAEs correlating with some changes. This dissertation aims to characterize and reduce the HAEs sustained by contact sport athletes with a specific focus on football players.</div><div><br></div><div>Studies of middle school and high school football players revealed that there are likely offsetting effects that result in similar HAEs between the two groups. As one plays at higher levels of play with typically bigger, stronger, faster athletes that should result in higher magnitude HAEs, there is likely an improvement in tackling technique used at higher levels that make it so there are similar HAEs among different levels of play. Examining middle school football and high school football and girls’ soccer athletes indicate that players that play on two teams (i.e. a player that plays both Varsity and Junior Varsity) may be at an increased risk for neurological changes due to over-exposure. It was revealed when studying post-collegiate football the up stance offensive linemen may help reduce the frequency of HAEs compared to the down stance. However, the skill of the offensive lineman needs to be accounted for to determine if it is beneficial for players to start in this stance.</div><div><br></div><div>Repetitive HAEs (rHAEs), whether due to body or direct head impacts arising from participation in contact sports, are correlated with alterations in white matter health. Fractional anisotropy (FA) and mean diffusivity (MD), two metrics used to assess white matter structural integrity, typically change in opposite directions (one increases while the other decreases) after brain injury. This study investigated the manner in which participation in American football affects the percentage of white matter exhibiting the four possible change combinations: increased FA, increased MD; decreased FA, increased MD; increased FA, decreased MD; decreased FA, decreased MD. Diffusion tensor imaging data of 61 high school football and 15 non-contact athletes were analyzed. After a season of participation, football athletes exhibited a significantly greater percentage of deviant voxels in each of the four categories than were observed from test-retest of non-contact athletes. Even prior to a season of participation, football athletes exhibited significantly more voxels in each of the categories, relative to controls. Of particular concern is that voxels exhibiting jointly decreased FA and MD—a change typically associated with cell death—were observed at a significantly higher rate within football athletes than non-contact athletes. This finding suggests that rHAEs may increase the incidence of cell death, and argues for the greater adoption of methods aimed at reducing mechanical loading on the brain from rHAEs, both through reduction of the number of HAEs, and development of better protective equipment.</div><div><br></div><div>Rugby is a sport that is very similar to football in terms of physicality and overall objective, but there are marked differences in protective equipment and style of play. These differences in protective equipment result in different tackling rules and styles between the two sports that may influence the effect repetitive HAEs can have on neurological health. Therefore, the HAEs experienced over the course of the season by New Zealand collegiate (ages 16+) rugby athletes were characterized. The number of HAEs were compared by position (forward vs. backs) and the peak translation acceleration (PTA) of the HAE was analyzed by position, possession (offense vs. defense), and cause of HAE (tackle vs. ruck). Forwards (although not significantly) tended to sustain more HAEs than backs, but there were no differences in the magnitude of the HAEs by any of the types of comparisons. However, when considering possession and type of HAE simultaneously, it was found that HAEs in a defensive ruck are more severe than those sustained in an offensive ruck. This could be a potential place to work on player technique to reduce the PTA during these situations.</div><div><br></div><div>There are numerous studies that have utilized accelerometers to quantify head motion during a contact event, but a current gap in the field is quantification of the impact force. In order to capture high force events, an instrumented helmet using strain was built to capture this data. Strain gauges were adhered to the inside of a Riddell Speedflex helmet shell and then mounted onto a Hybrid III Headform for testing. The helmet was hit at four different locations (front, right, back, and left) and at different impulse ranges (2-5 Ns, 5-8 Ns, 8-11 Ns, and 11+ Ns). The strain gauges were able to classify the location of the hit with about 95% accuracy and were correlated the impact peak force and impulse. This suggests that it is possible to build an instrumented helmet to be worn by a football player during collision events to capture real impact force and location data.</div>

Nearly 3.5 million kids play youth football every year in the United States, many in independent organizations with few or no rules for limiting head impact exposure in practices or competition. Studies have found potential long-term effects of repetitive head impact exposure from a young age, even in the absence of concussion. The best methods for reducing head impact exposure include a multi-pronged approach: limiting contact through rules changes, teaching proper technique for contact when it does occur, and designing equipment with better protective capabilities. Four youth football teams were studied for one season each using helmet mounted accelerometer arrays. Head acceleration data indicated that youth teams often have a small subset of players who account for a disproportionately large number of high-risk head impacts. As few as six players (6%) accounted for over 50% of all high-risk impacts seen in practice sessions. Technique used during tackling and tackle-absorption had considerable effect on head acceleration. Both the tackler and ball carrier were found to be at greater risk for high magnitude head impacts when exhibiting poor form as defined by specific tackling recommendation criteria. These data suggest that individualized interventions encouraging proper form, especially for a subset of impact-prone players, may be beneficial in reducing high magnitude head impact exposure for an entire youth football team. This is especially critical because a majority of high-risk impacts are experienced in practice at the youth level. Results from this work could be applied by coaching staffs in youth football leagues to increase the safety of their athletes. / MS

Mechanical trauma to the brain, both big and small, and the method to protect the brain in its presence is a crucial field of research given the large population exposed to neuronal trauma daily and the benefit available through better understanding and injury prevention. A population of particular interest and risk are youth athletes in contact sports due to large accelerations they expose themselves to and their developing brains. To better monitor the risk these athletes are exposed to, their accumulation of head acceleration events (HAEs), a measure correlated with harmful neurological changes, was tracked over sport seasons. It was observed that few significant differences in HAEs accumulated existed between players of ages from middle school to high school, but there did exist a difference between sports with girls' soccer players accumulating fewer HAEs than football players. This highlights to risk youth athletes are exposed to and the importance of improved technique and individual player size. To better monitor HAEs for each individual, a novel head segmentation program was developed that extracts player specific geometries from a single T1 MRI scan that can improve the accuracy of HAE monitoring. Acceleration measures processed with individualized head model versus those using a standardized head model typically displayed higher accelerations, highlighting the need for individualized measure for accurate monitoring of HAEs and risk of neurological changes. In addition to the large accelerations present in contact sports, the small but constant strains produced by neural implants embedded in the brain is also an important field of neuro-mechanical research as the physical properties of neural implants have been found to contribute to the chronic immune response, a major factor preventing the widespread implementation of neural implants. To reduce the severity of the immune response and provide improved chronic functionality, researchers have varied neural implant design and materials, finding general trends but not precise relationships between the design factors and how they contribute the mechanical strain in the brain. Performing a large series of mechanical simulations and Cotter's sensitivity analyses, the relationships between neural design factors and the stain they produce in the brain was examined. It was found that the direction which neural implants are loaded contributes the most to the strain produced in the brain followed by the degree of bonding between the brain and the electrode. Directly related to the design of electrodes themselves, it was found that in most cases reducing the cross-sectional area of the probe resulted in a larger decrease of mechanical strain compared to softening the implant. Finally, a study was performed quantifying the resting micromotion of the brain utilizing a novel method of soft tissue micromotion measurement via microCT, applicable within the skull and the throughout the rest of the body.

Young football players are hypothesized to experience damage to the brain and brain function from repeated subconcussive head acceleration events (HAEs) during practices and games. Such damage may cause delayed cognitive and mental problems. Resting state fMRI (rs-fMRI) is an effective non-invasive method to detect alterations in brain functional connectivity. Seed-based rsfMRI analysis using the central node of the default mode network (DMN) as the seed is a common approach to measuring intrinsic changes of the DMN, accepted as a key network in brain function. Seed-based rs-fMRI analysis of the DMN was used to explore how age, HAE intensity, and HAE counts influence brain connectivity in youth athletes (ages 12-18). Middle school and high school football players and peer controls were studied using rs-fMRI before and after one season of competition. An identifiability matrix was generated from the seed-based connectivity matrix, allowing measurement of similarity between pre-season and post-season functional connectivity. The consistency of seed-based brain functional connectivity we observed across the season of play for players has no statistically significant difference from controls. The identifiability matrix exhibited no relation to the number and magnitude of any subset of HAEs experienced which rejected our hypothesis. Another finding is that high school football players exhibited the largest percentage increase in identification from middle school football players in the somatomotor network over other resting-state networks.

<div> <div> <div> <p>Recent observations of short-term changes in the neural health of youth athletes participating in collision sports such as football (boys) and soccer (girls) have incited a need to explore structural alterations in their brain tissue volumes. Studies have shown biochemical, vascular, functional connectivity, and white matter diffusivity changes in the brain physiology of these athletes that are strongly correlated with repetitive head acceleration exposure from on-field collisions. Here, research is presented that highlights regional anatomical volumetric measures that change longitudinally with accrued repetitive head impacts. A novel pipeline is introduced that provides simplified data analysis on a standard-space template to quantify group-level longitudinal volumetric changes within these populations. For both sports, results highlight incremental relative regional volumetric changes in the sub-cortical cerebrospinal fluid that are strongly correlated with head exposure events greater than a 50G threshold at the short-term post-season assessment. Moreover, longitudinal regional gray matter volumes are observed to decrease with time, only returning to baseline/pre-participation levels after sufficient (5-6 months) rest from collision-based exposure. These temporal structural volumetric alterations are significantly different from normal aging observed in gender and age-matched controls participating in non-collision sports. Future work involves modeling safe repetitive head exposure thresholds with multimodal image analysis and understanding their underlying physiological functioning. A possible pathophysiological pathway is presented highlighting the probable metabolic regulatory mechanisms. The interdisciplinary nature of this work is crucial to understand this pathology accurately and aid healthcare, sport professionals in the future. It is evident that continual participation in collision- based activities may represent a risk wherein recovery cannot occur. Even when present, the degree of the eventual recovery remains to be explored but has strong implications for the well-being of collision-sport participants. </p> </div> </div> </div>