Head injuries are keeping professional hockey players off the ice for longer, indicating either more severe injuries, or a tougher medical regime, according to a study released on Monday.

With the National Hockey League playoffs under way after a season where jarring head shots grabbed headlines, researchers said the number of concussions was leveling off. But the ice time a player loses more than doubles with each subsequent concussion, so there were more absences.

“Either concussions are becoming more severe or physicians are becoming more conservative with their management decisions,” said Brian Benson, a physician at the University of Calgary’s faculty of kinesiology and the lead author of the report. “We’re uncertain of the exact reason but it’s certainly an observation of the study.”

The report now goes to the NHL’s concussion working group, which will examine ways to prevent concussions, or work out how to respond when they do happen.

“The goal in hockey in general is to reduce the risk of this potentially devastating injury without necessarily changing the nature of the game that millions love and enjoy watching,” Benson said.

“You don’t want to make haphazard decisions but you certainly want to base it on evidence and try to reduce this foreseeable, predictable risk.”

The league has faced many calls for tougher penalties for potentially career-ending hits to the head, including some this season after a March incident in which Max Pacioretty of the Montreal Canadiens was injured after a body check that sent his head into a stanchion.

He suffered a concussion and fractured vertebra.

Sidney Crosby, Canada’s gold-medal goal-scorer in the 2010 Winter Olympics, has been off the ice since suffering a concussion in January.

The researchers worked with the NHL and NHL Players’ Association to analyze 559 doctors’ reports of concussions suffered by players between 1997 and 2004. Their findings are published in the Canadian Medical Association Journal.

The researchers estimated that there were 1.8 concussions per 1,000 player hours, a number that leveled off through the study period.

The most-often reported symptom was headache at 71 percent. But players also reported dizziness, nausea, neck pain, fatigue, blurred vision or amnesia. Some 18 percent lost consciousness.

For each recurrent concussion, the typical number of days lost increased by 2.25 times.

Benson has worked with the NHL and its players union since 1997 studying the medical science behind brain injury.

(Editing by Rob Wilson and Janet Guttsman)

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By Jeffrey Jones

CALGARY, Alberta