In Vivo Evaluation of Wearable Head Impact Sensors

Abstract

Inertial sensors are commonly used to measure human head motion.(R1–3) Some sensors have been tested with dummy or cadaver experiments with mixed results, and methods to evaluate sensors in vivo are lacking. Here we present an in vivo(R3–10) method using high speed video to test teeth-mounted (mouthguard), soft tissue-mounted (skin patch), and headgear-mounted (skull cap) sensors during 6–13g(R1–20) sagittal soccer head impacts. Sensor coupling to the skull (R1–3) was quantified by displacement from an ear-canal reference. Mouthguard displacements were within video measurement error (<1mm), while the skin patch and skull cap displaced up to 4mm and 13mm from the ear-canal reference, respectively. We used the mouthguard, which had the least displacement from skull (R1–5), as the reference to assess 6-degree-of-freedom skin patch and skull cap measurements. Linear and rotational acceleration magnitudes were over-predicted by both the skin patch (with 120% NRMS error for amag, 290% for αmag(R1–6)) and the skull cap (320% NRMS error for amag, 500% for αmag(R1–6)). Such over-predictions were largely due to out-of-plane motion. To model sensor error, we found that in-plane skin patch acceleration peaks in the anterior-posterior direction could be modeled by an underdamped viscoelastic system. In summary, the mouthguard showed tighter skull coupling than the other sensor mounting approaches(R1–7). Furthermore, the in vivo methods presented are valuable for investigating skull acceleration sensor technologies.

Similar head impact acceleration measured using instrumented ear patches in a junior rugby union team during matches in comparison with other sports

“…The positioning of the XPatch over the mastoid process was important to ensure that the sensor was not activated by enhanced soft-tissue effects when impacts occurred. 38 The XPatch contained a low-power, high-g, triaxial accelerometer with 200g maximum per axis and a triaxial angular rate gyroscope that was used to capture 6 degrees of freedom for the linear and rotational accelerations over time of the head's center of gravity for all impacts that occurred during match participation. The time history incorporated 3 axes (x, y, z) of acceleration and 3 axes of velocity.…”

“…The XPatch has a strong correlation with peak linear acceleration (PLA; r 2 = 0.93) 38 with a normalized root square error of 18%, but may overpredict PLA and peak rotational acceleration (PRA) by 15g ± 7g and 2500 ± 1200 rad/sec 2 , respectively. Nevins et al 30 reported that the XPatch had good agreement with PLA but underestimated PRA by more than 25%.…”

“…22 Following the match, the XPatch was removed from the player and the data were downloaded to the Injury Management Software (X2Biosystems), which enabled the raw accelerometer data to be transformed to the head's center of gravity by using a rigid-body transformation for linear acceleration and a 5-point stencil for rotational accel eration. 22,38 The biomechanical measures of head impact severity consisted of impact duration (measured in milliseconds), linear acceleration (g), and rotational head acceleration (rad/sec 2 ). The resultant linear acceleration is the rate of change in the velocity of the estimated center of gravity of the head attributable to an impact and the associated direction of the motion of the head.…”

The Influence of Head Impact Threshold for Reporting Data in Contact and Collision Sports: Systematic Review and Original Data Analysis

“…117 These differences may invariably influence the results of the published studies as, although some studies report the linear threshold as 14.4g, they may actually be recording from 10g…”

Impact Sensing Headgear-A Physical Approach to Provide Critical Information

“…Accelerometer-based sensing with the device affixed to the athlete either on the cranium or in the mouth is in current use. The results of impact sensing from these technologies vary with the location and specific properties of the device tested, and in all cases respond to acceleration rather than force [8]. In addition, much of the presently available, accelerometer-based devices rely on wireless transmission of impact events, whereas the forcerecording strips reported here do not transmit data wirelessly, and provide information specific to the point of impact.…”