NHL players lost an average of 10 days of playing time in a third of concussion cases from 1997 to 2004, a new study finds.

The study in Monday's issue of the Canadian Medical Association Journal showed the number of injuries levelled off over seven regular NHL seasons. It also pointed to clinical signs and symptoms that predicted players being off the ice for more time.

Researchers at the University of Calgary are analyzing more recent NHL data.

In the published study, predictors of time off ice included:

• Headache.
• Low energy or fatigue.
• Memory loss.
• Abnormal neurological exam.

"Our results suggest that there was a trend toward a gradual increase in post-concussion time loss over the study period," said lead author Dr. Brian Benson, a researcher and physician at the Sport Medicine Centre in the University of Calgary's faculty of kinesiology.

"One trend we saw was that while the number of concussions levelled out over the study period, the amount of time loss appeared to gradually increase over the years, which may be an indication of either greater severity or greater caution in treatment," he added in a release.

The study raised repeat concussion as an issue, noting typical time loss in days increased 2.25 times during the study period for every recurrent concussion.

Specifically, the study looked at 559 concussions suffered by NHL players in regular season games, based on physicians' reports from every team in the league.

More precaution needed

Among those who lost time, 31 per cent of the concussions led to players missing more than 10 days of competition.

In 11 per cent of those lost-time instances, the players had continued to play and then later reported symptoms to medical staff after the game. Degree of NHL players' symptoms among those who lost regular playing time due to concussion. CMAJ

There were an estimated 1.8 concussions per 1,000 hours of playing time, the researcher estimated.

"Our findings also suggest that more conservative or precautionary measures should be taken in the immediate post-concussion period, particularly when an athlete reports or experiences a post-concussion headache, low energy or fatigue, amnesia, recurrent concussion or many different post-concussion symptoms, or when the athlete has an abnormal neurologic examination," the study's authors concluded.

During the study period, concussion rates decreased from a peak of 7.7 concussions per 100 players during the 2000-2001 season to 4.9 per 100 players in 2003-2004.

NHL weighs changes

The researchers said they hope the findings will offer practical information for team doctors about specific concussion signs and symptoms that could point to potentially more serious concussions.

Since the concussion program by the league and its players union evolved during the seven-year period of the study, only the signs, symptoms and physical exam findings that were consistent from season to season were included.

The league has faced calls for tougher penalties, most recently following the Zdeno Chara hit on Max Pacioretty last month that caused a severe concussion and fractured neck, as well as Sidney Crosby's concussion in January.

In March, the NHL announced new concussion rules, such as requiring trainers to conduct a quick test with players in a quiet area.

Monday's NHL decision not to suspend Vancouver Canucks forward Raffi Torres after his hit on Chicago Blackhawks defenceman Brent Seabrook shows a related debate among spectators on what's considered a head shot hasn't been settled, said Hockey Night in Canada's Scott Morrison.

Youth bodychecking ban

The way professionals play hockey is imitated in junior hockey, according to the authors of a second study appearing in the same issue that calls for bodychecking to be eliminated except for elite hockey players aged 16 and older.

"The fact is that the vast majority of concussions, and hockey injuries overall, at all levels of play, are caused by legal bodychecking," wrote Dr. Syd Johnson of Dalhousie University in Halifax.

"It's time to break that cycle and teach youths to play in a way that emphasizes skill and protects their brains, so they'll be prepared to do the same when they grow up," Johnson concluded.

Up to 25 per cent of all junior hockey players in one season suffered concussions, a recent study suggested.

About 500,000 young people in Canada play hockey in organized leagues. Only one in 4,000 youth hockey players makes it to the professional league, according to Hockey Canada, the country's central governing body for youth hockey.

Given those odds, Johnson argues it isn't worth subjecting so many young players to high risk of injury.

With files from CBC's Chris Brown