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Cumulative Effects of Repetitive Head Impacts Quantified in Study

High school football players appear to be exposed to a greater volume of high-level head impacts during practices compared with games, according to a new study published in the online edition of the Annals of Biomedical Engineering.

The study, conducted by scientists at Wake Forest Baptist Medical Center, sought to quantify the cumulative effects of repetitive head impacts that high school football players endure. The researchers equipped the helmets of 40 high school players with accelerometers that measured both linear (front-to-back and side-to-side) impacts and rotational impacts.

A total of 16,502 head impacts were collected over the course of the season, which included 33 practices and 14 games (two of which were scrimmages). During the 33 practices, there were a total of 9,167 head impacts, while the remaining 7,335 head impacts occurred during the 14 games.

The researchers used these head-impact data to create a metric called Risk Weighted Cumulative Exposure (RWE), which could capture players' exposure to the risk of concussion over the course of a football season. They used RWE to measure players' risk of injury because of linear and rotational accelerations separately, as well as the combined probability of injury associated with both.

The head-impact frequency was found to be greater during games compared to practices, with an average of 15.5 head impacts per game and 9.4 per practice. However, the median risk of concussion based on both linear and rotational forces was found to be greater during practices than games.

"This metric gives us a way to look at a large number of players and the hits they've incurred while playing football," said lead author Joel Stitzel, chair of biomedical engineering at Wake Forest Baptist Medical Center, in a statement. "We know that young players are constantly experiencing low-level hits that don't cause visible injury, but there hasn't been a good way to measure the associated risk of concussion."

Just over 60 percent of the team had greater than 50 percent total RWE attributed to practice impacts, according to the study. Those findings, the scientists suggest, may encourage teams and leagues to reduce exposure to head impacts during practices.

This isn't the first study to suggest that youth football players' concussion risk is greater during practices than games. In February 2012, a joint Virginia Tech-Wake Forest study found that the hardest hits for youth football players tended to occur during practice.

The Boston-based Sports Legacy Institute called that same month for all youth sports organizations to limit the amount of head contact that student-athletes endure. The institute proposed putting youth athletes on a "hit count" to reduce the risk of concussion and long-term brain damage, specifically saying that no athlete younger than 18 should "be exposed to more than 1,000 hits to the head exceeding 10 g's of force in a season."

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