In-helmet Accelerometer Research
Real-time accelerometer data collection is a novel method available to researchers who are attempting to better understand the biomechanics of mTBI, but the earlier study designs were limited and unable to provide a realistic and meaningful interpretation of the data. For example, in a multisport study, Naunheim et al.attempted to investigate the linear accelerations sustained by high school student-athletes – specifically, an ice hockey defenseman, football offensive lineman, football defensive lineman, and a soccer player. A triaxial accelerometer was inserted within a football and ice hockey helmet, and linear acceleration values were recorded during actual play. The data obtained from the soccer player allowed for limited interpretation firstly because there was no method of affixing the accelerometer to the player’s head so the soccer player wore an instrumented football helmet. Secondly, game data were not captured; instead, the soccer player was asked to head 23 balls kicked to him or her at a standardized velocity. The mean linear acceleration measured in the football and ice hockey players was 29.2g and 35.0g, respectively.
Duma et al. were the first to use acceleration-measuring technology in helmets for large numbers of athletes during normal practice and game situations. His group used the Head Impact Telemetry (HIT) System technology (Simbex, Lebanon, NH) incorporated within the Sideline Response System (Riddell Corp.; Elyria, OH). A major component of the HIT System is a unit composed of six spring-loaded single-axis accelerometers that are inserted into football helmets (Fig. 1). Duma et al. reported the magnitude of head impacts to be 32 ± 25g. This contrasts the range of 20g to 23g in a similar sample of Division I collegiate football players studied by our University of North Carolina research group using the HIT System technology. The football-related data reported by Naunheim et al. also are much higher than our observed football impact data, which averaged 22g of linear acceleration.[ A statistically significant difference was then observed by comparing the linear acceleration of head impacts of football players across three different event types. Head impacts sustained in helmets-only and full-contact practices were significantly higher than those sustained in games or scrimmages. This finding was somewhat surprising, given that our earlier investigations found the incidence of concussion to be 6–8 times higher in games than practices. Furthermore, our preliminary data in youth ice hockey players suggest that mean linear accelerations average about 19g. Although the earlier study by Naunheim et al. represented an important advance toward real-time data collection, her group was limited by a very small sample and did not transform the data to render it to be normally distributed; this tends to overestimate the actual linear acceleration values measured and leads us to believe that the actual values were probably closer to those captured in the more recent studies involving the HIT System.
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