With a flash of steel and a few quick zigzags, a large bearded man on skates lowers his head to crash at more than 20 miles per hour into the upper body of another player, knocking him to the ice — out cold.

An inherent part of professional ice hockey in North America, such high-impact collisions between opposing players make serious head injuries a regular aspect of the sport, although the National Hockey League (NHL) has attempted in recent years to reduce the number of concussions.

However, those efforts have failed according to a new study from Canadian researchers, as just as many players continued to incur mild traumatic brain injuries in the two seasons following the 2010 introduction of "Rule 48," which prohibits lateral and blind side hits to an opponent targeting the head.

"Concussions remain a serious risk for NHL... players," the researchers wrote. "Despite recent actions taken by the NHL to introduce Rule 48 regulating bodychecking to the head, concussion incidence among NHL hockey players has not decreased."

The team of researchers, from Toronto and Halifax, recommended that the NHL either address the scope and enforcement of the bodychecking rule or make other changes to reduce the head injury rate in the sport, similar to the milder style of play of European ice hockey. Furthermore, investigators found that most concussions on ice were not caused by blindsided hits to the upper body, making Rule 48 ineffective in lowering the numbers.

But researchers also said the NHL might simply "need more time," as enforcement of the new bodychecking rule — as well as Rule 41, prohibiting direct hits to a defenseless opponent against the boards — might change the style of play over time.

Toronto Maple Leaf's general manager, Brian Burke, pondered after the 2010-2011 season how rule changes might change the game over time. "We've got to eliminate the dangerous hits without taking hitting out," he said. "It's a very slippery slope."

A 50-game suspension for an illegal hit, however, would put a "chilling effect" on other types of hitting. "If people want to that, they can just go to Europe," Burke said. "There is an appetite for longer suspensions. I think we need to raise the bar for those type of hits without getting crazy," he said.

In the study, investigators used official game records and team injury reports to compare concussion and concussive head injuries in the 2010-2011 and 2011-2012 seasons, finding a lower rate of concussions in the 2009-2010 season than after the rule change. Sixty-four percent of the concussions were caused by bodychecking, while only 28 percent were caused by illegal incidents, such as blindside hits targeting the head.

Below is video footage of some recent NHL concussion hits:

Source: Donaldson L, Asbridge M, Cusimano MD. Bodychecking Rules and Concussion in Elite Hockey. PLoS ONE. 2013.