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UNIVERSITY OF CALIFORNIA, IRVINE Effect of Ball Inflation Pressure and Padded Headgear on Ball-Head Impacts in Water Polo and Soccer THESIS submitted in partial satisfaction of the requirements for the degree of MASTER OF SCIENCE In Mechanical Engineering by Wyatt Xavier Moscoso Thesis Committee: Doctor David J. Reinkensmeyer Doctor James Hicks Associate Professor Lorenzo Valdevit 2017 © 2017 Wyatt Xavier Moscoso DEDICATION To My Family and Friends In recognition of their unending support Perfection is not attainable, but if we chase Perfection We can catch Excellence -Vince Lombardi ii TABLE OF CONTENTS Page LIST OF FIGURES iv ACKNOWLEDGMENTS v ABSTRACT OF THE THESIS vi INTRODUCTION 1 METHODS 4 Apparatus & Experimental Setup 4 Experimental Procedure and Statistical Analysis 7 RESULTS 8 DISCUSSION 12 Effect of Ball Pressure 12 Effect of Headgear 13 Impact Reduction Mechanisms 15 Enough to Make a Difference? 16 Limitations and Future Studies 17 Conclusion 18 BIBLIOGRAPHY 19 iii LIST OF FIGURES Page Figure 1 Experimental Setup 5 Figure 2A Average Linear Impact Acceleration – Cap On 9 Figure 2B Average Linear Impact Acceleration – Cap Off 9 Figure 2C Average Angular Velocity - Cap On 9 Figure 2D Average Angular Velocity – Cap Off 9 Figure 3A Linear Acceleration – Cap On vs. Cap Off 10 Figure 3B Angular Velocity – Cap On vs. Cap Off 10 Figure 4A Histogram of Z-Scores – Cap On 10 Figure 4B Histogram of Z-Scores – Cap Off 10 Figure 5A Average Linear Impact Acceleration – Soccer 11 Figure 5B Average Angular Velocity – Soccer 11 iv ACKNOWLEDGMENTS I would like to acknowledge all of the individuals who had a part in the completion of this thesis. I thank Dr. David Reinkensmeyer of UCI’s MAE department for introducing me to this project, and taking on the task of being my advisor. His support through some of the rougher spots, such as the legal fiasco fall quarter, the IRB hassle, and my leave of absence, as well his ability to answer any questions I had (or know where to look) was invaluable. I very much appreciated his consistent, positive attitude for the past 3 years. I thank Tyler Jacobs, Jordan Schmitz, Nick Cecchi, T.J. Oros, and Sherilyn Bumatay for being stellar team members and friends. I started this project alone, but in retrospect, I have no idea what I would have done without them. I thank Dr. James Hicks of the Ecology and Evolutionary Biology department for being a second advisor to us through his constant interest in and support of the experiment, as well his readily available knowledge about everything water polo related. His funding of all rentals and equipment was crucial to the experiment’s completion. I thank Patrick Puzzuto of DTS and Xavier Hernandez of KARCO for their exceptional responsiveness and knowledgeability about their products. When we had accelerometer difficulties, they were out on-site within a few days, completely replaced our accelerometers, provided us with a new DAS, and gave us a full software walkthrough. I thank Mike Gratopp of Humanetics for his customer support throughout our lease transaction and availability to discuss any issues we had. His understanding as we held the ATD for 2 weeks over the 1 week deadline is also greatly appreciated. I thank Coach Scott Juniper of UCI Athletics Departments for graciously allowing us to borrow much of their equipment, including balls, pressure gages, air pumps, and most importantly, the ball launcher. I thank Paul Hope of UCI Facilities & Operations for allowing us to use the soccer field for testing the entire time of our lease. I thank Associate Professor Lorenzo Valdevit for agreeing to be on my thesis committee and taking the time out of his schedule to help review my manuscript. Finally, I thank Terry Wang and Colin Sledge for their very helpful meetings, which always pushed us to stay on track with our timeline and organization. I appreciate the friendly atmosphere they created for us, where we could bounce ideas off of them and get pertinent, insightful feedback for our posters and presentations. v ABSTRACT OF THE THESIS Concussions in Water Polo and Soccer By Wyatt Xavier Moscoso Master of Science in Mechanical Engineering University of California, Irvine, 2017 Doctor David J. Reinkensmeyer In the sports of water polo and soccer, the effects of ball inflation pressure on head impact forces have received little attention. Determining this relationship may help minimize the results of ball-head contact in these sports and become important for preventing concussion. We studied the effect of ball inflation pressure (35-117 kPa; 5-17 psi) and headgear on head linear impact acceleration and angular velocity using an instrumented, anthropomorphic, test dummy head. Water polo and soccer balls were shot at the forehead at 17.4 to 24.6 m/s (39 to 55 mph), the speeds of the fastest shots in elite water polo, as well as speeds which are typical for heading from goalie punts in competitive soccer. Overinflating the ball beyond the recommended pressure for each sport – 90 to 117 kPa (13 to 17 psi) for water polo, 55 to 76 kPa (8 to 11 psi) for soccer - significantly increased linear impact acceleration by 7% for both water polo and soccer balls (p < 0.001). Underinflating the ball from 90 to 69 kPa (13 to 10 psi) for water polo and 55 to 34 kPa (8 to 5 psi) for soccer significantly decreased linear impact acceleration by 8.5% for water polo and 13.5% for soccer (p < 0.001). Headgear is shown to reduce impact forces by 22% and angular velocity vi by 23.5%. These results suggest that appropriately inflating the ball and/or wearing padded headgear may help reduce the prevalence of brain trauma in water polo and soccer. vii INTRODUCTION Approximately 50% of the 3.8 million concussions experienced in the US each year are sports-related 14,18. Mechanisms of brain injury due to head impact in sports are still not fully understood 17, but impulsive linear and rotational accelerations are widely thought to contribute to brain injury 17,19,21. Such accelerations may stretch and damage axons within the brain, leading to transient neurologic dysfunction. Even when head impact does not result in immediately observable symptoms of concussion, some studies suggest that repetitive sub-concussive hits in sports cause structural and functional brain changes over time 1,2,22,28. Recurrent head impacts may be associated with the development of chronic neurodegenerative disorders such as chronic traumatic encephalopathy, and may result in executive dysfunction, memory impairment, depression, apathy, poor impulse control, and eventually, dementia 12,32. Finding ways to reduce the effects of sub-concussive and concussive hits in sports is, therefore, an important goal, and will likely require attenuating the magnitude of head impact accelerations whenever possible. Soccer and water polo present a unique opportunity because of the nature of the player-ball interaction in these sports. Soccer is the only sport in which players intentionally maneuver the ball with their head. In addition, soccer has the greatest rate of sports-related concussions for women 13. In water polo, the plane of ball movement is nearly aligned with the players’ heads 32, and thus water polo defenders, especially goalies, frequently sustain hits to the head from shots. The first concussion survey of water polo players recently found that 47% of goalies and 36% of all water polo players have experienced at least one concussion, with an average of around two concussions experienced per respondent 5. Beyond this recent study and the apparent 1 prevalence of concussions seen in the sport, water polo currently suffers from a scarcity of data regarding concussion, exacerbated by the lack of systematic reporting of traumatic brain injury at the club, high school and collegiate levels 5. Two candidate strategies for reducing ball-head impact are to reduce ball inflation pressure and/or to wear padded headgear. Surprisingly little research has been done on the effect of ball inflation pressure on head impact accelerations in soccer. Studies investigating the role of ball inflation pressures have used experimental 3,29 and theoretical approaches27. The results were equivocal showing either ball inflation pressure did not influence impact characteristics or significantly reduced impact forces. There has been no research on the role of ball inflation pressure pertaining to water polo. The second strategy is the use of padded headgear. Several studies have examined the effect of headgear in soccer with varying conclusions. Some of these studies have suggested that headgear may play a role in attenuating impact for more forceful blows at higher speeds 7,22, while others have concluded that headgear is not effective21. There have been no published studies on the effectiveness of padded headgear in reducing impact forces in water polo. The goal of this study was to determine the effects of ball inflation pressure on impact forces when the ball hits the head at the highest range of speeds expected in water polo and soccer. We also tested whether a padded water polo cap could reduce impact forces, to determine if we could replicate benefits found for padded headgear in soccer. Instead of using theoretical simulations, which make assumptions about the physics of impact,26 or human subject experiments, which are difficult to justify in the case of delivering repeated hits to the head at high speeds, we used an instrumented, anthropomorphic test dummy 2 head. Such test dummies have undergone years of refinement to improve their bio-fidelity, and are the standard for head impact testing in the transportation industry. 3 Methods Apparatus and Experimental Set-up The experiment consisted of launching water polo and soccer balls inflated to varying pressures at varying speeds at an anthropomorphic test dummy (ATD) head/neck unit (Figure 1, Hybrid III 50th Percentile Male Anthropomorphic Testing Dummy, Humanetics, Plymouth, Michigan).

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