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A shock-absorbing football helmet system being developed at the University of Michigan could blunt some dangerous physics that today’s head protection ignores.
The engineering researchers making the system, called Mitigatium, were recently funded by a group that includes the National Football League. Their early prototype could lead to a lightweight and affordable helmet that effectively dissipates the energy from hit after hit on the field. Current helmets can’t do this, and that’s one of the reasons they aren’t very good at preventing brain injury, according to the university.
“Today’s football helmets are designed to prevent skull fractures by reducing the peak force of an impact,” said Ellen Arruda, U-M professor of mechanical engineering and biomedical engineering. “And they do a good job of that. But they don’t actually dissipate energy. They leave that to the brain.”
Sports like football present big challenges for the designers of protective head gear. To dissipate energy, a helmet typically has to deform, like the bike version cracks in a collision. And disposable helmets aren’t practical for football players.
When a bike helmet breaks, it’s absorbing what’s called “impulse”—a secondary effect of an initial force. Impulse, which gives objects momentum, is what transmits kinetic energy through a system. It takes into account not just force, but also how long that force was applied. To calculate impulse, you multiply the average force by the length of time it was exerted on the subject.
For head protection to be most effective against the speeds and weights of players on a football field, these researchers say it has to block impulse.
They’re not the first to say this. They’ve found medical studies from 70 years back that blame impulse for damage from football-style, quick impacts. Yet today, helmet makers and health researchers alike tend to rely on other factors. For example, new helmet designs are approved based solely on the peak force they can withstand.
“Everyone is focused on the force of an impact and only the force,” Arruda said. “But they’ve found that when they measure peak force on the surface of the skull, they can’t correlate that with brain injury. The reason is that force is only part of the story.”
Scientists and doctors don’t fully understand how a blow to the head translates to brain injury, but the U-M researchers say impulse is a big factor. Arruda and her colleagues have demonstrated this.
They’ve taken one of the first close looks at the mechanical features of impacts and blasts and how helmets and other armor might be designed to do a better job protecting sensitive structures. o do that, they built two-dimensional mock cross-sections of materials that stood in for the brain and skull in various helmet shells. Then they use a table-top collision simulator to test the different samples. They compared how much energy was transmitted through to the brain-type layer in their own helmet system and the status quo. They used a high-speed camera to help them observe how the brain model deformed in both systems.
“Some of the insight we got from this analysis was subtly different from how the helmet community thought about design, although we found examples in old medical literature that were consistent with our understanding,” said Michael Thouless, the Janine Johnson Weins Professor of Engineering in mechanical engineering and materials science and engineering.
In their experiments, the current helmet model did little to block impulse. The researchers could tell this by how much the speckled pattern on their brain layer distorted. The Mitigatium prototype, however, reduced impulse to just 20 percent of what got through to the brain model in the conventional helmet. Mitigatium reduced peak pressure to 30 percent. It lowered both by an order of magnitude, Arruda said.
Here’s how it works: It’s made of three materials that amount to more than the sum of their parts. The first layer is similar to the hard polycarbonate that’s the shell of present-day helmets. The second is a flexible plastic. Together these substances reflect most of the initial shock wave from a collision—most of the initial force. They also do something else unique and important: They convert the frequency of that incoming pressure wave to a frequency that the next layer can, in essence, grab ahold of and dissipate by vibrating. This third “visco-elastic” layer has the consistency of dried tar.
“We’ve come up with a totally new concept of how to make efficient impact-mitigating structures that could dissipate energy without being damaged,” Thouless said. “And we used basic concepts of mechanics to develop a fundamental understanding of how to protect delicate structures such as the brain.”
Late last year, the U-M team was one of five winners of the Head Health Challenge III, a competition to support the development of materials that better absorb or dissipate impact. Aside from the NFL, sponsors are Under Armour, GE and the National Institute of Standards and Technology. The U-M researchers received $250,000 to take their technology to the full prototype stage. Doctoral candidate Tanaz Rahimzadeh is also contributing to this project.
The researchers also point out that their system is extremely flexible, in that different materials could be used to tune different incoming pressure waves. They envision their approach to have applications for the military and other protective gear, as well as for playground surfaces.
A paper on some of these findings, titled “Design of armor for protection against blast and impact,” is published in the Journal of the Mechanics and Physics of Solids. Rahimzadeh is the first author.
To reduce the risk of concussion, researchers and others have sought ways to improve helmet technology as a way to resolve the problem.
A better solution may be to ditch the helmets altogether, according to a new study in the Journal of Athletic Training, the National Athletic Trainers’ Association’s scientific publication. Researchers investigated the effectiveness of helmetless tackling to reduce head-impact exposure in an NCAA Division I football program.
The study, partially funded by the NATA Research & Education Foundation, showed a 28 percent reduction in head impacts during practices and games. To review “Early Results of a Helmetless-Tacking Intervention to Decrease Head Impacts in Football Players,” please visit:
“Given proper training, education and instruction, college football players can safely perform supervised tackling and blocking drills in practice without helmets,” said Erik E. Swartz, PhD, ATC, FNATA, lead author of the study and professor and chair, Department of Kinesiology, University of New Hampshire. “This intervention also eliminates a false sense of security a player may feel when wearing a helmet. Younger players with less experience may require modifications to this intervention to realize a positive effect. While more research is needed, our results do show a reduction in head impacts during our one season of testing.”
The findings are from the first year of a two-year study in which 50 NCAA Division 1 football players at the University of New Hampshire were assigned to an intervention (25 athletes) or control (25 athletes) group. The intervention group participated in five-minute tackling drills without their helmets and shoulder pads as part of the Helmetless Tackling Training (HuTT) program. Drills occurred twice per week during preseason practices and once per week throughout the competitive season (16 weeks). The control group performed noncontact football skills with no change to their routine. All athletes were provided head-impact patch sensors worn on the skin and new helmets. Both groups were supervised by members of the football coaching staff. At the end of the season, the intervention group experienced an average 30 percent fewer impacts per exposure than the control group.
The notion of removing the football helmet for discrete and regular periods during practice to reduce head impact is counterintuitive to the sport, wrote the authors. “These findings elucidate the risk-compensation phenomenon and may help explain the behavior of spearing and the rise in catastrophic neck and head injuries that followed,” they added. “A football helmet is designed to protect players from traumatic head injury, but it also enables them to initiate and sustain impacts because of the protection it affords. While improving protective equipment in and of itself will not resolve the risk of concussion and spine injury in football, the solution may be found in behavior modification.”
High school and college football players can each sustain more than 1,000 impacts in a season, while individual youth players may sustain 100 during that same timeframe according to the study. “The extent to which this intervention may yield similar outcomes in younger players with less experience is still unknown. We are currently in the first year of a high school study focused on four high schools in New Hampshire,” adds Swartz.
“Should future research replicate our findings, the eventual adoption of helmetless-tackling training may improve public health and decrease the associated economic burden by reducing football-related head and neck injuries and the risk of long-term complications.”
Virginia Tech is leading a $3.3 million, multicenter, five-year study that will track head impact exposure in children — the largest and most comprehensive biomedical study of youth football players to date.
Funded by the National Institutes of Health’s National Institute of Neurological Disorders and Stroke, researchers will track on-field head impacts and accelerations using sensors installed in hundreds of players’ helmets.
A new addition to the study will be mouth guards, which also will have sensors installed in them. Players at six schools in three states also will receive neuropsychological testing.
Leading the study is Stefan Duma, head of Virginia Tech’sDepartment of Biomedical Engineering and Mechanics, part of the College of Engineering.
Duma and his multi-university team will focus on six teams of 9- and 10-year-old players in three states, following each team during a five-year period, as well as the players themselves until they reach the age of 14.
“This is the largest coordinated youth study with the most advanced combination of instrumentation, clinical and neuropsychological testing,” said Duma, one of the earliest pioneers to study the biomechanics of football player head injuries and creator of a groundbreaking safety ratings system for football helmets and hockey helmets.
“Collecting this data during the next five years will allow for evidence-based decisions across a range of applications, including improved clinical detection techniques as well as a solid foundation for our helmet rating programs and offer ways potentially to improve youth football helmet design,” added Duma. “We will work with Pop Warner and other national governing bodies to develop improved practice strategies.”
Participants will be instrumented with two high-tech sensor systems, one located inside the helmet and the other in the front part of the player’s mouthpiece, each measuring all head impacts and rotations during all practices and games.
Data will be transmitted instantly to researchers near the sidelines, monitoring all impact levels. All practices and games will be videotaped to match sensor data with actual visuals of on-field impacts. Participants will undergo neurocognitive examinations off-field, involving computerized tests, balance scores of postural stability, and survey data.
“This study will provide important translational outcomes including an improved understanding of the rotational kinematics during football head impacts in the youth population,” said Steve Rowson, assistant professor of biomedical engineering at Virginia Tech, who has worked with Duma for the past 10 years. “This can lead to improved injury risk functions that could be used across all sports as well as automobile safety applications.”
Virginia Tech researchers will monitor and collect data from two local Blacksburg recreational teams. Long-time study collaborators Wake Forest School of Medicine, part of Wake Forest Baptist Medical Center in North Carolina, and Brown University in Rhode Island will each monitor and collect data from two youth football teams in their respective region.
The two teams at Wake Forest School of Medicine are lead by Joel Stitzel and Jill Urban, with additional funding from the Childress Institute for Pediatric Trauma. At Brown University, Trey Crisco and Beth Wilcox lead the research efforts for their two teams.
Also leading the research team are Jonathan Beckwith and Rick Greenwald, founder of New Hampshire-based technology firm Simbex and Art Maerlender of the University of Nebraska Lincoln, who will head neuropsychology testing and collection.
As with earlier studies involving scores of Virginia Tech athletes, this study also will involve Mike Goforth, head athletic trainer, and Brett Griesemer, assistant trainer, both with Virginia Tech Athletics; Gunnar Brolinson, professor of sports medicine and head team doctor, and Marc Rogers, an associate professor of sports medicine, both with the Edward Via College of Osteopathic Medicine; and Eric Smith of the Department of Statistics with the College of Science at Virginia Tech.
Virginia Tech biomedical engineering doctoral students working on the study are Megan Bland of State College, Pennsylvania; Eamon Campolettano of Hicksville, New York; Jaclyn Press of Doylestown, Pennsylvania; Jake Smith of Pittsburgh, Pennsylvania; and David Sproule of Houghton, Michigan.
“Five years from now, the hope is that we have a very strong understanding of the severity and frequency of impacts for youth football,” said Campolettano, who joined Duma and Rowson’s research team earlier this year. “Further, we can use this data to design improved testing methodologies for youth football helmets.”
Simbex is supporting the Head Impact Telemetry System – or HITS, for short – instrumentation that is part of the Elyria, Ohio-based Riddell’s Sideling Response System that records head impact exposure.
HITS is an accelerometer array mounted against a player’s head, inside the helmet, that will be used to quantify linear and rotational accelerations. The system builds on technology previously used to measure head impacts of Virginia Tech football players since 2003.
Instrumented mouth guards purchased from a second private firm, Kirkland, Washington-based I1 Biometrics will be custom fit to each player. Called the Vector, the mouth guard uses accelerometers and gyroscopes to measure linear and rotational accelerations. Both HITS and Vector transmit data wirelessly in real-time to researchers on the sidelines.
Coordinating statistical analysis for the study, Virginia Tech’s Eric Smith added, “It is quite natural for statisticians to be part of projects such as this one as statisticians are partly ‘data engineers.’ We think a lot about the data collection as a process and work to ensure the quality of the data.”
The grant is awarded using funds from the National Institutes of Health’s Bioengineering Research Partnership (BRP). This is the second BRP for this research team, and it expands on a previous award from the Eunice Kennedy Shriver National Institute of Child Health and Human Development. The first BRP focused on collegiate football and hockey and resulted in more than 100 technical publications and presentations.
Duma and his research team have garnered international recognition during the past decade for creating a ratings system for adult football helmets, as well as a similar system for hockey helmets introduced this year.
Additionally, Duma is part of a $30 million national effort to combat concussions among college athletes and active military personnel.
The three-year project involves male and female NCAA student-athletes participating in football, women’s soccer, men’s soccer, and women’s lacrosse.
Virginia Tech’s Institute for Critical Technology and Applied Science provided support in developing the successful proposal submission to the National Institutes of Health, said Duma.