It takes less than a second, but the wrist shot in hockey is one of the hardest skills in sports to master. Just ask the Pittsburgh Penguins and the Detroit Red Wings who will face each other starting this weekend in the National Hockey League's Stanley Cup Finals. Both teams know the value of the "quick wrister" and the scoring chances it creates. Now, a team of Canadian (of course) researchers believe they have isolated the key components of a successful wrist shot using 3-D motion capture analysis.
Hockey players have a few different types of shots that they use when trying to score. The slap shot, with its big wind-up and speed is a fan favorite, but the quick, on-the-fly wrist shot can be deadly accurate and accounts for 23-37 percent of shots taken at the professional level. To send the puck into one of the four corners of the goal (and avoid the goalie), a player must be able to control not only its horizontal direction but also its height when aiming at the top corners. This precision has to happen while the puck is sliding on the ice independently of the player and his stick.
Professors David Pearsall and Rene Turcotte, along with graduate student Yannick Michaud-Paquette of McGill University wanted to find out how the mechanics of the hockey stick and blade affected the flight of the puck and be able to point to specific movement patterns which resulted in more accurate shots. As Turcotte told LiveScience, "Very little information exists describing the kinetics and kinematics of skating and shooting skills. We are for the first time learning about how skills are executed in an optimized fashion."
Their research appears in a recent edition of Sports Engineering.
Twenty five hockey players, ranging in skill from novice to varsity level players, were told to shoot pucks at targets located in the four corners of a goal until they had hit each target ten times. They were allowed 20 shots per target with their accuracy percentage recorded. Their stick and the pucks were marked with reflective stickers that could be seen by six 3-D motion capture cameras placed around the goal. Everything from the angle, pitch and yaw of the stick blade to the stick velocity and contact time between puck and stick were measured as possible variables for accuracy.
As expected, the successful shot percentages were evenly divided between the novices (as low as 27 percent) and the expert players (as high as 80 percent). When shooting at the bottom targets, the most significant variable that affected accuracy was the position of the puck on the blade when released. The novices tended to position the puck closer to the blade's heel, while the better players put it closer to the center of the curve in the blade, closer to the toe.
Hitting the top two corners of the goal was by far the most difficult task, with 20 percent less accuracy compared to the bottom corners. This makes sense as the third dimension of height is now added. Since the flight of the puck now is affected by gravity, the initial trajectory of the puck becomes important. Just like a baseball pitch, the faster the object travels, the flatter and more accurate the trajectory. Imagine the flight path of a fastball versus a curve ball. The team found that faster initial puck velocity when released from the stick significantly improved accuracy.
Also important was something called the blade's "roll angle" at puck release. Video of the expert players showed that when getting the puck ready to shoot they drag or draw in the puck and the stick's blade closer their feet. This would let them use their wrists more to give the stick that well known "flick." The beginner players would more often push the puck forward without any pre-shot adjustment closer to their body.
The McGill team sees potential for continuing their research to the point of giving practical coaching tips in the future. "Research in this area is relatively new and so many of the findings in our laboratory and in two or three others are producing new knowledge in this area," said Turcotte. "Our increased understanding will have implications for teaching and coaching and can help practitioners to teach players to optimize skill development."