Laboratory evaluation of a wearable head impact sensor for use in water polo and land sports

Abstract

The SIM-G is a waterproof head impact sensor that has been previously evaluated for use in a headband, but not yet in a mode of attachment suitable for water polo. For this study, a CADEX linear impactor was used to impact a Hybrid III headform while wearing either a headband or modified water polo cap, each housing a SIM-G. In both headgears, the SIM-G consistently underestimated peak linear acceleration ( p < .001) and peak rotational velocity ( p < .001), and consistently overestimated peak rotational acceleration ( p < .001) relative to the headform. These inaccuracies are consistent with previous evaluations of the SIM-G, but notably, impact magnitudes did not differ between the different modes of attachment ( p > .198). The proprietary SIM-G algorithm used for classifying false/true positives performed poorly at the back and crown impact locations in both the water polo cap and headband, but accuracy of this algorithm did not significantly differ between the water polo cap and headband (60.5% vs 49.4%, respectively). The SIM-G’s ability to correctly predict impact location also performed poorly in both headgears when impacts occurred at the crown location, but was significantly better overall in the water polo cap than the headband (80.2% vs 55.6%, respectively). These results demonstrate that the SIM-G exhibits shared limitations and a similar performance overall when placed in either a headband or water polo cap. Potential explanations for the inaccuracies of the SIM-G, as well as methods of optimizing its application in sports, are discussed.

A Dose Relationship Between Brain Functional Connectivity and Cumulative Head Impact Exposure in Collegiate Water Polo Players

“…These missing data might be particularly detrimental to estimating impact exposure sustained by goalies, the only position to report sustaining head impacts more frequently in practice than in games (6). It is important to note that the patterns observed with wCHI as an outcome measure were indistinguishable statistically from those incorporating only the frequency of head impacts (i.e., without consideration of the magnitude of those impacts), a relationship which could also be attributed to poor accuracy and reliability of the SIM-G sensors in estimating impact magnitude (40).…”

“…To meet the sensor manufacturer's specifications and recommendations, each SIM-G sensor was inserted into a player's water polo cap that had been modified to include a Velcro pocket designed to couple the sensor with the occipital protuberance. Laboratory evaluations of the SIM-G demonstrate that it can record peak linear and rotational acceleration when coupled tightly to the occipital protuberance in a headband (39), and the sensor performed comparably when secured using a water polo cap (40). Impact data were collected across 22 games (11 men's games; 11 women's games).…”

“…The sensors also feature a complex algorithm that aims to distinguish hit-related head movement from commonly occurring non-impact transients or false-positives (e.g., voluntary head movement, adjusting of headgear, sensor movements about the head) based on impact waveform topography. However, these algorithms have demonstrated poor reliability (40) and the filter was disregarded. Instead, six research staff members evaluated video recordings of all games to identify and eliminate false positives through a consensus process.…”

“…The authors are aware of the well-documented inaccuracies of head impact kinematics measured using head-worn inertial sensors (40). Therefore, we used the same analytical approach described above to relate changes in FC to the number of confirmed head impacts (nHI) each athlete sustained, without considering the magnitude of those impacts (see Supplemental Text 1).…”

Patterns of head impact exposure in men’s and women’s collegiate club water polo

“…However, these algorithms have performed poorly under ideal conditions in lab-based evaluations. 18 Therefore, all competitions were recorded from two camera angles, and the videos were later reviewed by research staff to eliminate false positives, confirm impact locations on the head, and identify impact mechanisms and player positions. A sensor was manually triggered by research staff in the view of both cameras at the end of each competition to provide a reference marker for use in synchronization of time stamps recorded by the sensors with the video footage.…”