Chinstraps Influence Head Impact Severity in Laboratory Facemask Impacts

Recent reports indicate that approximately half of the head impacts and one third of the concussions in American football occur due to contact with the helmet's facemask. Despite this, helmet innovations have primarily focused on improving attenuation of impacts to the helmet shell. During facemask impacts, the chinstrap goes into tension and materials in the chin cup are compressed. Various chinstraps are available to equip to helmets and the present study sought to conduct the first known evaluation of the influence of the chinstrap on facemask impact severity.

Fourteen different chinstraps were affixed to an identical American football helmet which was subjected to laboratory impact testing. Chin cup liner thickness and lengths of the top and bottom straps were measured for each chinstrap. A linear impactor delivered impacts at 3.0 and 7.4 m/s at a central facemask impact location while the helmet was worn by a medium NOCSAE headform. Head kinematics were recorded and used to compute the Head Acceleration Response Metric (HARM), a brain injury risk metric derived from linear and rotational head kinematics.

One-way ANOVAs revealed a statistically significant effect of chinstrap model on HARM at both impact velocities (p < 0.0001). Differences in HARM between chinstraps were as great as 35.4% at 3.0 m/s and 31.4% at 7.4 m/s. There was a statistically significant association between HARM and chin cup liner thickness at 3.0 m/s (p = 0.0002), indicating thicker chin cup liners resulted in lower HARM (R² = 0.706), but this trend was not observed at 7.4 m/s (p = 0.14, R² = 0.450). Top strap length was not significantly associated with HARM at 3.0 m/s (p = 0.689) or 7.4 m/s (p = 0.541). There was a statistically significant association between HARM and bottom strap length at 3.0 m/s (p = 0.004, R² = 0.523), but this trend was not observed at 7.4 m/s (p = 0.799).

Overall, we report that the chinstrap can significantly influence the severity of facemask impacts in American football helmets across multiple impact velocities. Increasing chinstrap liner thicknesses and strap lengths may yield reductions in kinematics-based injury risk metrics at some impact velocities. Further investigation of the chinstrap system is warranted to inform future chinstrap design toward improved impact attenuation.