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Introduction The purpose of this study was to compare the rotational blunt impact performance of an anthropomorphic test device (ATD: male 50% Hybrid III head and neck) headform donning an Advanced Combat Helmet (ACH) between conditions in which the coefficient of static friction (μs) at the head-to-helmet pad interface varied. Materials and Methods Two ACHs (size large) were used in this study and friction was varied using polytetrafluoroethylene (PTFE), human hair, skullcap, and the native vinyl skin of the ATD. A condition in which hook and loop material adhered the headform to the liner system was also tested, resulting in a total of five conditions: PTFE, Human Hair, Skullcap, Vinyl, and Hook. Blunt impact tests with each helmet in each of the five conditions were conducted on a pneumatic linear impactor at 4.3 m/s. The ATD donning the ACH was impacted in seven locations (Crown, Front, Rear, Left Side, Right Side, Left Nape, and Right Nape). The peak resultant angular acceleration (PAA), velocity (PAV), and the Diffuse Axonal Multi-Axis, General Evaluation (DAMAGE) metric were compared between conditions. Results No pairwise differences were observed between conditions for PAA. A positive correlation was observed between mean μs and PAA at the Front (τ = 0.28; P = .044) and Rear (τ = 0.31; P = .024) impact locations. The Hook condition had a mean PAV value that was often less than the other conditions (P ≤ .024). A positive correlation was observed between mean μs and PAV at the Front (τ = 0.32; P = .019) and Right Side (τ = 0.57; P < .001) locations. The Hook condition tended to have the lowest DAMAGE value compared to the other conditions (P ≤ .032). A positive correlation was observed between the mean μs and DAMAGE at the Rear (τ = 0.60; P < .001) location. A negative correlation was observed at the Left Side (τ = -0.28; P = .040), Right Side (τ = -0.58; P < .001) and Left Nape (τ = -0.56; P < .001) locations. Conclusions The results of this study indicate that at some impact locations kinematic responses can vary as a function of the friction at the head-to-helmet pad interface. However, a reduction in the coupling of the head-helmet pad interface did not consistently reduce head angular kinematics or measures of brain strain across impact locations. Thus, for the ACH during collision-type impacts, impact location as opposed to μs seems to have a greater influence on head kinematics and rotational-based measures of brain strain.

Girls’ lacrosse participation and head injury rates have increased within the past decade. In response, optional headgear was implemented following the recently developed ASTM International lacrosse headgear performance standards. It remains unknown how lacrosse headgear responds to blunt impacts after use. Our purpose was to compare the peak linear acceleration between girls’ lacrosse headgear conditions (pristine and used) during blunt impacts. Pristine headgear (n = 10) were tested in their original condition and used headgear (n = 10) were worn for an entire competitive season. A Cadex Monorail Impactor impacted all headgear following ASTM standards (F1446-15b, F2220-15, and F3137-15) in the required testing locations. A 2 × 7 repeated-measures analysis of variance compared peak linear acceleration among headgear conditions and impact locations with a simple effects analysis planned comparison. There was no difference between headgear conditions for peak linear acceleration (pristine: 47.12 [13.92] g; used: 46.62 [14.84] g; F = 2.11, P > .05). A main effect for impact location (F = 983.52, P < .01), and an interaction effect of condition and impact location (F = 12.79, P < .01) were observed. All headgear, regardless of condition, met the ASTM performance standard. This suggests that headgear performance may not degrade subsequent to a single season of high school girls’ lacrosse.

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