Comparison of Head Impact Exposure Measures in Football from Two Different Accelerometry Devices

Abstract

The Head Impact Telemetry System (HITS) has been used to measure real-time head impact exposure (HIE) in football for the past decade. More recently, several lighter and less expensive head impact sensors have entered the retail market, intended for individual player monitoring of HIE. The ability of these products to accurately measure HIE in the field is largely unknown PURPOSE: To compare measures of HIE in football obtained from the GForce Tracker (GFT), a retail head impact sensor, with those derived simultaneously from HITS. METHODS: Seventeen middle school football players (12-14 yr) wore helmets outfitted concurrently with HITS and GFT during twelve consecutive practices and one game in a season. HITS utilized a six single-axis accelerometer array, whereas GFT used one triaxial accelerometer to measure the frequency, linear acceleration and location of head impacts. RESULTS: Total impacts measured by HITS and GFT were 476 and 3264, respectively. Median head impacts per player were significantly correlated between HITS and GFT (r = 0.77; P < 0.001), but were significantly lower when measured by HITS (28 ± 17 vs. 192 ± 96 impacts/player, respectively)(P < 0.001). The 50th and 95th percentiles of linear acceleration were 21.1g and 55.1g for HITS and 17.8g and 50.5g for GFT. Mean linear acceleration measured by HITS (26.0 ± 14.5g) was significantly greater than that measured by GFT (22.6 ± 13.9g)(P < 0.001). Head impact frequency registered by HITS was highest to the front of the helmet (48%), followed by the back of the helmet (25%), the side of the helmet (15%) and the top of the helmet (11%); whereas GFT measured impacts occurred most frequently to the side of the helmet (33%), followed by the back of the helmet (28%), the front of the helmet (28%) and the top of the helmet (11%). CONCLUSION: This is the first study to compare HIE measured concomitantly with GFT and HITS in football. There were several notable discrepancies in head impact frequency, magnitude and location distribution measured by the two devices that would drastically affect the interpretation of individual player HIE. These findings highlight the need for additional research to determine the on-field validity and practical utility of all sensors used for real-time monitoring of head impacts in football.