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ORLANDO -- As concern has grown in recent years about the long-term ramifications of concussions in athletes, changes in rules have sought to alleviate some of the potential hazards. The results thus far have been mixed, two new studies presented here suggested.

In one study, a single team's experience during the period 1996 through 2012 suggested that the rule change in 2007 forbidding players to return to play the same day after having a concussion had the intended effect. But in the other, a rule change regarding helmet fit appeared not to make any difference.

Before the 2007 season, players were allowed to continue in the game after sustaining a concussion, and during the years 1996 to 2006, there were 17 instances of same day return. However, after 2006, no player had same day return, according to , of the National Sports Medicine Institute in Lansdowne, Va.

In addition, after 2006, players with concussions had significantly longer time until they returned to play, averaging 7.95 days compared with 3.72 days previously (P<0.001), Bernard reported at the .

Each year, there are an estimated 1.6 to 3.8 million sports-related concussions in the U.S., representing 5% to 9% of all sports-related injuries. In the early 1990s, a number of early player retirements prompted the NFL to form the mild Traumatic Brain Injury (mTBI) committee, including athletic trainers, team physicians, neurologists, neurosurgeons, and scientists. They sought to define and conduct research into mTBI in an effort to reduce these injuries, Bernard explained.

To examine a single team's experience with concussions since this increased emphasis on safety, therefore, he and his colleagues conducted a retrospective review of prospectively collected data over a 17-year period.

The total number of concussions sustained by team members during that time period was 116, in 89 players. This amounted to 6.8 concussions per season, with 8% occurring during practice sessions. In games only, the rate was 2.9 per game, and 19 players had multiple concussions, he noted.

Between 1996 and 2008, seven players had more than one concussion per season, but after that time, only one player had more than one per season.

Most of the concussions occurred during pass plays (45%), and the highest frequency was seen for wide receivers, cornerbacks, and offensive linemen.

"In our study, the length of time spans the initial recognition and formation of the mTBI committee and extends beyond previously reported data," Bernard concluded.

Proper Helmet Fit

A different pattern was seen in another study presented at the meeting, in which a rule change regarding helmet fit among high school football players had no apparent effect.

"A rule established in 2012 aimed at ensuring proper helmet fit resulted in no change in the proportion of helmets without proper fit," said , of Temple University in Philadelphia.

"Rather, there was an increase in the number of symptoms and concussions were lasting longer after the rule change," he said.

The rule, enacted by the National Federation of State High School Associations football rules committee, indicated that if the helmet comes off completely after impact, the player has to sit out one play for adjustments to be made.

"The committee made this rules change after reviewing data from multiple states regarding the frequency of helmets coming off during live-ball play. It is the committee's hope that this serves notice for schools to properly fit players with helmets to reduce the incidence of these situations," the committee said at the time.

"We know from the literature that modern helmets do influence the risk of concussions, with two studies both showing that a newer helmet decreased the risk. Specifically, one type has 40% thicker padding over the zygoma and mandible regions, affecting how the helmet fits on the face and head," Greenhill said.

To further examine the possible relationship between helmet fit and concussion, he and his colleagues analyzed data from 4,580 concussion reports in the National High School Sports-Related Injury Surveillance System over a 9-year period beginning in 2005.

A total of 3.3% of the athletes had helmets presumed to fit improperly, and the analysis showed that players with poorly fitting helmets had a mean of 5.3 symptoms versus 4.5 following concussion (P=0.004), he reported. The symptoms also lasted longer, he added.

The specific symptoms associated with improper fit included higher rates of drowsiness (RR 1.46, P=0.005), hyperexcitability (RR 2.38, P=0.047), and sensitivity to noise (RR 1.88, P<0.001).

When the researchers compared the type of padding in the helmet, they found that players with air bladder padding had more sensitivity to light and noise, whereas those who had gel or foam padding more often reported drowsiness or loss of consciousness.

The rule "has failed to effectively improve the percentage of helmets that fit or the severity of concussions sustained in high school football," Greenhill said.

"Team physicians, athletic trainers, coaches, and high school officials should require proper oversight of helmet fit in high school athletes in order to decrease concussion severity and duration," he concluded.