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CHARACTERIZING AND REDUCING HEAD ACCELERATION EVENTS IN CONTACT SPORTS
thesisposted on 07.05.2021, 11:39 by Taylor A LeeTaylor A Lee
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
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.
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.
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.
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.
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.