Reliability and accuracy of helmet-mounted and head-mounted devices used to measure head accelerations

Abstract

The attention given to brain injury has grown in recent years as its effects have become better understood. A desire to investigate the causal agents of head trauma in athletes has led to the development and use of several devices that track head impacts. In order to determine which devices best measure these impacts, a Hybrid III headform was used to quantify the accuracy for translational and angular accelerations. Testing was performed by mounting each device into the helmet as instructed by its manufacturer, fitting the helmet on the headform, and impacting the helmet using an impulse hammer. The root mean square error for the peak translational acceleration varied with location. The worst root mean square error for a head-mounted device was 74.7% while the worst for a helmet-mounted device was 298%. Headmounted devices consistently outperformed those mounted in helmets, suggesting that future sensor designs should avoid attachment to the helmet. Deployment to a high school football team affirmed differences between two of the device models, but strongly indicated that head-mounted systems require further development to account for variation between individuals, the relative motion of the skin, and helmet-sensor interactions. Future work needs to account for these issues, refine the algorithms used to estimate the translational and angular accelerations, and examine technologies that better locate the source of the impact.

Comparative Analysis of Head Impact in Contact and Collision Sports

“…The xPatch accelerometer used in the present study appears in eight published studies, 60,62,65,66,[70][71][72][73] three of which test biomechanical validity in different settings. 60,62,73 Wu and coworkers compared the in vivo performance of the xPatch against video capture in a simulated low-impact soccer setting; that study examined 25 impacts, one impact location, one mastoid placement location, and one xPatch device.…”

“…60,62,73 Wu and coworkers compared the in vivo performance of the xPatch against video capture in a simulated low-impact soccer setting; that study examined 25 impacts, one impact location, one mastoid placement location, and one xPatch device. In one subject, they found the xPatch overestimated individual linear and rotational accelerations (normalized root-mean-squared error [RMSE] of 120% for PRLA and 290% for PRRA) in ways likely related to the viscoelastic properties of that individual's soft tissues.…”

“…62 Using a Hybrid III headform model, Cummiskey and coworkers performed the most thorough comparison to date comparing the reliability and accuracy of helmet-mounted against head-mounted accelerometer systems. 73 The study included both the commonly used HITS and the xPatch, among other helmet-and head-mounted accelerometer systems. Cummiskey and coworkers delivered 140 impacts across seven impact locations to evaluate each device and sensor location.…”

“…The xPatch did produce considerable error across impact locations (RMSE of 8-58% for PRLA and 11%-350% for PRRA), but across devices, sensor locations, and impact locations, the xPatch produced RMSE that were considerably lower than, or at least comparable with, the RMSE produced by the HITS. 73 The Hybrid III system used by Cummiskey and coworkers does not account for xPatch measurement error caused by skin displacement, 62 nor does is account for HIT system measurement error caused by differential helmet fitment. 74 As a prelude to a live play soccer study, McCuen and coworkers 60 evaluated xPatch performance on a Hybrid III headform; this study examined 250 impacts, spread over five impact locations, in two mastoid placement locations, and included data from five different xPatch devices.…”

Evaluation of skin-mounted sensor for head impact measurement

“…These have been used in studies of head impacts in unhelmeted sports such as soccer 21,22 and rugby. 23 To date, the majority of studies on the accuracy of head impact sensors have used a Hybrid III headform 24,25 fitted with a reference a triaxial linear accelerometer and a triaxial gyroscope positioned at the centre of gravity. The Hybrid III dummy headform has a viscoelastic skin, the response of which is strain independent up to strains of 20%.…”