Impact attenuation capabilities of new and used football helmets

Football helmets are expected to break down with use, and reconditioning recommendations are required to be stated by manufacturers. However, the degree of change in helmet impact mitigation performance as a function of usage is not generally known. Therefore, this study aimed to compare the ability of football helmets to attenuate impacts after a single season of regular collegiate use to unused helmets. Three never-used Riddell^® Speed™ helmets were tested and compared to three used helmets which had been used during one season of Division 1 collegiate football. Helmets were tested at three velocities (3.46, 4.88, and 5.46 m s⁻¹) on six locations in ambient temperature, simulating National Operating Committee on Standards for Athletic Equipment certification drop tests. The interaction between helmet age and location during all three velocities (P⩽ 0.0001), indicating that there were differences in Gadd severity index (GSI) between new and used helmets after accounting for location-specific differences. Similar analysis for peak linear acceleration (PLA) found significant interactions for all three velocities (P⩽ 0.003). Additional analyses found differences in velocity-dependence for several impact locations. In most cases, used helmets yielded lower GSI and PLA relative to new helmets. The reduction in impact metrics for used helmets indicates initial break-in with impact mitigation benefits, but the long-term consequences of continued use are unclear. The implications of these differences on injury risk and susceptibility remain unknown; however, the results suggest that further studies could inform helmet reconditioning guidelines and development of new smart materials designed to monitor and/or prevent breakdown in padding.