Head injuries in full-contact sports such as hockey and (American) football are becoming ever more common as are discussions of their long-term impact. While this has been mostly chatted up in the sporting community, it has now crossed over to the general public after the noted political columnist George Will highlighted some of the new concerns in a recent editorial. [*]
While rule changes have been made to try and reduce this problem, there are also approaches taking advantage of technology, specifically gel rheology. A Georgia company, Guardian now makes a gel-filled cap that covers a football helmet and, at least based on initial, anecdotal reports from players, seems to pretty much eliminate head trauma. Gels are well-known for absorbing and dissipating energy repeatedly, making them the ideal choice for this application. From a rheological perspective, soft gels have a dominant viscous behavior and a minor elastic behavior. The viscosity is important as it is the sink for the impact energy. Elasticity is recoverable energy, something that should be minimized, but if there is too little of it, the gel would not recover its shape repeatedly. (Imagine how unworkable a cap filled with water or even a very viscous liquid would be. It would all flow to the bottom and provide no protection up high.) A key question is how long these gels maintain their integrity, as all the impact energy will eventually break down the elastic component, making them of little use.
Since the caps go over the helmets, the caps are only used in practice and taken off for games. But players practice more than play actual games, so while not perfect, the impact(grin) of the caps is significant. It seems like the caps are too thick for them to be be placed inside the helmet and therefore be used all the time. That would be a nice second generation product or something for a competitor to invent.
[*] While the column is almost entirely about chronic head injuries, I was much more taken aback by this quote:"For all (football) players who play five or more years, life expectancy is less than 60; for linemen it is much less." I used to think my sport, bicycle racing, was tough because of the old saying in the peleton that riding the Tour de France takes a year off your life. But for football players, it looks like a year in the NFL takes 3 years off your life. Yikes.