For Canadians, hockey is more than a pastime - it's a way of life. From a young age, many Canadians learn to skate. It can become as natural as walking to some, but the reality is that skating - and especially hockey - can take its toll on the human body.
Over the years, there have been several attempts to document the physical stress that skating, and specifically the game of hockey, can inflict. But there has always been an obvious and prohibitive obstacle: How do you conduct delicate, scientific research in the cold, on ice?
The Ice Hockey Research Group (IHRG), working out of McGill University in Montreal, found the answer to exactly that question when it turned to motion-capture company Vicon.
Mocap on Ice
The IHRG was created to evaluate the ergonomic and mechanical function of skates, sticks, and protective equipment in respect to performance and safety when used by people on the ice. A research partnership with Bauer Hockey, Ltd. and the Natural Science and Engineering Research Council of Canada (NSERC) provides both financial and testing materials, which has enabled the development of a unique graduate biomechanics program focused on human performance measures of ice hockey equipment.
The problems with filming skaters on ice are numerous. The cold temperatures and humidity can wreak havoc on delicate equipment over time, and attempting to create a temporary and portable solution involves placing wires and other objects on the ice, which are hazardous for the skaters. Previous studies have attempted to re-create the movements of a hockey player using synthetic ice or a skating treadmill, but these lacked the validation of what it is actually like on the ice. It also limited the strides of people on skates, which on ice tend be around 5 meters (16.4 feet).
In 2014, Dr. David J. Pearsall, IHRG director and associate professor of kinesiology and physical education at McGill University, decided to risk the ice and try Vicon's motion-capture cameras and software. The IHRG team began by re-creating an ice rink using synthetic ice in order to get a sense of where the cameras needed to be placed and how they should be positioned; then once they were confident that they had the right configuration, they prepared for the real thing.
"The Vicon setup on the ice replicated the in-lab configuration on a larger scale," explains Philippe Renaud, IHRG research assistant. "This included extra safety measures, such as added weights to tripods for greater stability and suspended cable bridging over the skating ice path, plus special gloves to type on the computer in the cold. It worked out really well."
The Vicon system initially consisted of T-Series cameras running Nexus software. Once the team knew where everything was going, they still needed to be able to get in and out quickly and efficiently. According to Pearsall, the process was similar to a pit crew team in motor car racing.
"Ice time is costly. We can't leave the cameras set up permanently, so we have to set up, test, and take everything down within three to four hours," says Pearsall. "Everyone knows their jobs. We've got it down to a fine art."
Hitting the Ice
The first on-ice study conducted by the IHRG compared the skating start biomechanics of male ice hockey players with different levels of skill and experience. Since then, the IHRG has completed and published a second study, authored by Jaymee Shell, a master's graduate student at McGill University at the time. Shell studied the biomechanical differences between male and female players.
As with other sports analyses, the motivation was to better understand the optimal movement techniques for skating performance, as well as to identify potential factors that may be implicated in lower body injuries.
"As reported in prior running research, frontal plane differences between genders in hip and knee movements exist," say Shell. "So, we wanted to look at male and female ice hockey players and see if similar lower body kinematic differences existed or were greater."
The indoor ice rink's cold temperatures and high humidity were challenging for the cameras. There was the fear that the reflection from the ice would obscure marker tracking, but the equipment had no issues. The study represents a major achievement in 3D mocap, as the team was able to expand its range and calibrate a large 15x3x2-meter (50x10x6.5-foot) capture volume on the ice to record skating kinetics, with high intra-trial reliability. They did run into an issue, but the team was able to turn to Vicon application engineer John Porter, who Shell says, "saved her project."
"It wasn't the camera's fault at all - the cameras did exactly what they had to do," Shell says. "But having the Vicon support through the study was really invaluable. I can't praise the support team enough for what they did. I might still be labeling my data if it weren't for them!"
Following Shell's study and the results it produced, the IHRG decided to incorporate some of her methods and include female athletes in more of its studies.
Soon after Shell completed her study, the IHRG upgraded its system to include a Vantage and Vero optical camera, bringing the total number of cameras to 18. Soon after the upgrade, the IHRG expanded its studies to include puck shots, which brought with it the added risk of a puck bouncing back and hitting a camera. To compensate, the target nets were placed far enough back out of the capture area to reduce the risk of any collisions.
The team later added a Bonita camera alongside the Vantage to overlay the video with stick figure motions, making it easier to communicate their findings with others. EMG and force sensors were later introduced, all synchronized through Vicon software.
"To date, we've achieved a 15-meter (50-foot) FOV over the ice surface," Pearsall explains. "In skating, when you're at full speed, you can do 15 meters in two strides. As well, the increased pixel count and resolution of the Vantage cameras helps maintain the resolution needed to track the full-body marker set."
The IHRG's success has also led to studies into other fields beyond hockey, including working with groups to better understand how footwear performs on snow and ice. With the help of the Vicon cameras, the team is able to collect more data than ever before, which could prove to be invaluable to people who consider the ice a second home.