Head impact sensors, widely used by researchers and increasingly by athletes in games and practices to quantify head impact frequency and magnitude, may be a valuable tool for data collection, but verification of data via a second source, such as video, should also be utilized to confirm accuracy.

That was one of the takeaways from a recent study conducted by researchers at George Mason University and MedStar Sports Medicine Research Center. The findings were shared during last week’s US Lacrosse Sports Medicine Symposium in Baltimore.

The study examined impact data collected on boys’ and girls’ high school and youth players during the 2014 and 2015 seasons, with 48 males and 35 females sampled.

Among boys’ players, 1,060 impacts were recorded by the sensors during two seasons of game play. Of these, 690 (65%) impacts were confirmed as “true impacts” using video.

Among girls’ players, 180 impacts were measured by the sensors, and 58 of these (32%) were confirmed as “true impacts” using video. The game video was recorded by trained videographers using high-definition video cameras.

Dr. Shane Caswell, an associate professor of athletic training at George Mason University and director of the school’s Sports Medicine Assessment, Research & Testing (SMART) Laboratory, served as one of the lead researchers on the study and presented the findings at the Symposium.

“I think it’s fair to say that using sensor data only could yield research with inflated numbers regarding impacts,” Caswell said. “The impact must be corroborated in order to feel confident that the data is legitimate.”  

Analysis by the researchers indicated that the sensors registered a high number of false positives. All impacts measured by the sensors were reviewed by the research team.  A “true impact” was identified as having met the following criteria: a) linear acceleration measuring 20g or greater, b) the player was identified on the field, and c) the impact mechanism could be clearly identified.

Many of the non-verified impacts were categorized as the following:

• Impacts recorded by the sensors during play but no impact was observed on video.
• Impacts occurring while play was stopped (dead ball/time out situations).
• Impacts occurring while a player was on the sideline and not in the game.
• Impacts occurring during post-goal celebrations.
• Impacts occurring during halftime.

“Sensors don’t know whether an impact is valid or invalid,” Caswell said. “Measurements need to be combined with video corroboration for verification.”

Some of the other findings that the researchers identified based on the data collected by the sensors and verified via video.

• In both boys’ and girls’ lacrosse, midfield players suffer the most impacts.
• In boys’ lacrosse, the number one impact mechanism is player-to-player contact (67%).
• In girls’ lacrosse, the number one impact mechanism is stick contact (43%).
• Boys’ have more impacts than girls and have impacts at higher magnitudes.
• On average, boys players had seven confirmed impacts to the head greater than 20g per player per season.
• On average, girls players had 1.7 confirmed impacts to the head greater than 20g per player per season.
• Ball contacts were a small percentage of impacts and most frequently occur to goalies, not field players, in both boys’ and girls’ games.
• Only one concussion occurred during game play during the two years of analyzed data.

While not discounting the value that sensors offer as a research tool to determine the frequency and magnitude of impacts, the study demonstrates the benefit of using video to cross-verify the impact data recorded by the sensors.

The researchers also warned that that athletes in collision sports relying on the sensors as a warning system for possible concussive impacts may be basing their evaluations on inaccurate data.

“Impact sensors are really cool emerging technology, but there’s still a lot that we need to learn,” Caswell said.

2016 Research Report

A fuller summary of the findings from this research study can be accessed online as part of the 2016 Research Report, published by US Lacrosse’s Center for Sport Science.

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