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 / 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.

Existing classes of centrifugal clutch concepts were reviewed. The pseudo-rigid-body model (PRBM), rigid-body replacement synthesis, force-deflection analysis, compliance potential evaluation, and compliant concept evaluation were used to develop effective new centrifugal clutch concepts. These methods helped develop and model four novel compliant centrifugal clutch designs, model two existing designs, and identify a concept with excellent potential for low-cost centrifugal clutch applications. This concept, the floating opposing arm (FOA) clutch, doubles the torque capacity metric relative to existing compliant designs. Torque and engagement speed models for this clutch were developed and verified against four prototype clutches. Additional novel designs devel-oped through this work have lower torque capacities, but also show good potential because of other unique characteristics. All of the designs were prototyped and tested to measure their torque-speed relationships.