A new study finds that the amount of time NHL players missed because of concussions increased from 1997 to 2004. The report published Monday in the Canadian Medical Association Journal, the largest and most detailed analysis of concussions in hockey, examined physician reports from seven regular seasons. There were a total of 559 concussions during regular-season games, a concussion rate of 5.8 for every 100 players, or an estimated 1.8 concussions per 1,000 player-hours. "We found some interesting trends -- one being a gradual increase in post-concussion time loss over the seven years of study," said lead author Dr. Brian Benson of the Sport Medicine Centre at the University of Calgary's faculty of kinesiology. "That may be due to the concussions being severe or physicians being more conservative in their return-to-play decisions."