Helmets at the Sochi Olympics: The science of safety
By Neale McDevitt
Helmets have already gotten a fair bit of attention at the Sochi Games. Early on, there was controversy when the IOC ruled that athletes had to remove stickers and decals paying tribute to Canadian freestyle skier Sarah Burke, who died in a training accident two years ago, from their helmets, skis and snowboards. In recent days, a lot of focus has turned to the artistry on display on the helmets of the skeleton athletes, who – like today’s hockey goalies – adorn their headgear with a wide range of images, from stylized flags and patriotic images, to animal prints and, of course, a fair number of skulls.
But all this attention on what goes on a helmet takes away from its most important function; protecting what goes in it.
“Helmet design has become more sophisticated, yet still a lot of athletes are getting concussions,” says David Pearsall, Co-Director of the McGill Ice Hockey Research Group and an expert in biomechanics. “The question remains: what are we missing in term of helmet testing measures?”
To this end, a portion of Pearsall’s research focuses on testing the efficacy of hockey helmet designs and the materials used to make them. “We are different means of measuring impact mechanics than those currently being used,” says Pearsall.
Traditional methods to test hockey helmets, for example, require fitting an artificial headform instrumented with an accelerometer that measures just that, acceleration of impact (expressed in gravitational units or Gz). Researchers then subject the helmet and headform to a variety of controlled impacts and assess the resulting impact Gz of the whole head. Typically, an impact Gz must fall below a specified threshold, before a helmet can be certified by any number of standards agencies, including the Canadian Standards Agency (CSA).
“This approach has worked really well in preventing traumatic injuries like skull fractures and subdural hematomas,” says Pearsall, “but in terms of concussions, not too much.
“On the mid to lower continuum of impact energies, with concussions you don’t see a gross morphological ‘ah-ha, there it is!’ failure like you would in the case of a skull fracture,” he says. “Instead, brain damage occurs at the microscopic level involving micro-tears of neural tissues, and disruption of axon synaptic neurotransmitters that are linked to cognitive problems. That’s why it’s hard to clinically identify these problems and why it’s also hard to mechanically try to evaluate whether certain interventions are effective or not.”
That’s why other mechanical variables need to be considered. Several lead research labs are examining head angular acceleration and/or Finite Element Modeling of helmet/head/brain impacts. Alternatively, Pearsall and recently graduated PhD student Ryan Ouckama began evaluating impacts in a different way; that is, using a sensor array attached to a headform’s surface that quantifies how impact energy is dispersed across the skull surface.
Various helmet designs and material were then tested to see how effectively they could absorb the primary focal impact as well as the subsequent global head Gz. “We’ve adapted techniques to actually quantify the different foams and helmet designs that dynamically interface with the head’s surface and examined the difference between a blunt impact versus a ballistic one like a puck hitting you in the head,” says Pearsall. “With our mapping technique we can show how different types of helmet models and different types of foam have a distinct impact signatures.
“High impact focal stresses are thought to be of concern, as brain regions immediately below these impact points may be at higher risk of injury. Surprisingly, few people have tried to measure this before but now we can see how well the impact contract is spread out over the surface area and duration of impact,” says Pearsall.
All helmets, great and small
Watching the Sochi Olympics, viewers will see a variety of helmet designs, each one very specific to a particular sport. “Several sports have their own standards to match the impact events typical to their event,” says Pearsall. “The helmets used by downhill skiers, for example, are more robust because they are looking at much greater impact energy. By necessity, they have to be bulkier and heavier.”
And therein lies the biggest challenge for helmet designers – creating equipment that will keep competitors safe without impeding performance. “You could make really wonderful helmets in terms of impact protection but they would be really big and heavy and people just wouldn’t use them,” says Pearsall. “The tricky part is to make equipment that is acceptable to the users.”
Ah, the users – the wild card element in the concussion discussion. In his lab, Pearsall can control all the variables and help design and test the most solid pieces of protective equipment. But once a helmet is in the hands of an athlete, be they gold medal contenders or weekend warriors, they are only effective if they are used properly. “Human behavior can nullify any good design,” says Pearsall.
Watching Canada’s heart-stopping 2-1 win over Latvia in men’s hockey on Feb. 19, viewers saw virtually every skater on the ice playing with a chinstrap that was dangerously loose – a scene repeated in every NHL game. “Helmets are tested with the chinstraps nice and tight. But as soon as you loosen it like that, all bets are off,” says Pearsall. “How many times do you see a player fall to the ice after being tripped or checked and his helmet is knocked loose? It is a very dangerous situation because the helmet gives a person a false sense of security if it isn’t being used correctly.”
Pearsall also notes how other researchers have observed how player’s attitudes and on-ice comportment can change once they strap on their protective gear. “Another topic that often comes up when people talk about injury prevention is this idea of ‘risk compensation,’” he says. “Each individual has their own acceptable risk level that they are willing to put up with. But it has been observed that, as soon as people put on protective equipment, they may change their behaviors because they feel safer and they think they can be riskier. They may body check harder and with little regard for others and there is more high sticking because people are wearing cages. We can try to fix a problem by making a helmet mechanically better but until individual and group behavior is addressed, many of those gains will be nullified.
“I’m not one to say Don Cherry is right, but he might be on to something here,” says Pearsall with a chuckle.
The shelf life of a helmet
Like that container of Greek yoghurt lurking at the back of your fridge, your helmet has a certain shelf life. Some helmets, like those used by cyclists should be replaced after one significant impact because, even though it might not show any signs of wear-and-tear, the structure has been compromised.
But other, more robust helmets, like those used in hockey and football, have been designed to last – within limits. Pearsall has also studied the effects of time on hockey helmets, literally storing various helmets on a shelf for over a decade to see what – if anything – would happen.
“We found that up to five years the helmets were very stable. But by year 11 there were some issues,” says Pearsall. “The glues were starting to dry out and the foam was changing – just by sitting there. The CSA has put a five-year lifetime on these products because after that they do change.”
None of this matters much to the professional hockey players in Sochi who will change their helmets on a fairly regular basis. But for the average person playing recreational hockey, the cost sometimes outweighs safety concerns. “When you see the obvious signs like the foam is shifting because the glue is drying out, or there’s cracking in the shell – then that product is no longer effective in protecting you,” says Pearsall. “People who say ‘I don’t want to buy a new one’ are risking their own well-being.”
Category: Other News