How Shell Add-On Products Influence Youth Football Helmet Performance

Introduction: : Youth athletes experience up to 1.9 million sports-related concussions every year, 49% of which are due to football, making it the leading contributor. The differences in physiology and neurological responses to head impacts in youth populations compared to adults prevent the extrapolation of data relating to head trauma in adults to the youth population. Due to these differences, modified test conditions have been incorporated into helmet evaluations to assess youth populations more accurately. Shell add-on products are growing in popularity, and at the varsity level, they have shown a reduction in peak linear acceleration (PLA), peak rotational acceleration (PRA), and injury risk compared to control helmet conditions. The Guardian Cap XT and the SAFR Helmet Cover are intended for use on youth helmets, however, the effectiveness of shell add-ons in reducing concussion risk in youth football is unknown. This study aimed to evaluate the overall efficacy of shell add-on products at a youth football level using impact speeds representative of youth football impacts. Ultimately, this study can help consumers and manufacturers make informed decisions and guide product development regarding shell add-on products in the youth population.

Materials and

Methods: : Three youth football helmets were tested under a control (no add-on), single add-on (add-on applied to the helmet), and double add-on condition (add-on applied to the helmet and impactor face) (Figure 1). The VICIS Youth Zero2 was not tested with the SAFR Helmet Cover. Pendulum impact testing was completed with a curved nylon impactor face using the small NOCSAE headform connected to a 5th-percentile female Hybrid III neck mounted on a sliding mass to represent the effective torso mass of a 50th-percentile 10- to 12-year-old boy. Four impact locations (front, front boss, side, and back) were tested at impact speeds of 2.3, 3.4, and 4.9 m/s (Figure 1). Each test configuration was repeated seven times with two helmet model samples. This yielded 360 control, 600 single add-on, and 600 double add-on tests, totaling 1560 tests. The headform was instrumented with a six-degree-of-freedom sensor package mounted at the headform center of gravity, consisting of three accelerometers and a tri-axis angular rate sensor. Resultant PLA and PRA were calculated for each test. A previously published youth-specific risk function was used to estimate concussion risk based on PLA and PRA. Separate linear mixed-effect regression models, with a significance level of α < 0.05, compared helmet and impactor shell add-on conditions, including location, speed, and helmet shell add-on model as fixed effects and helmet model as a random effect for PLA, PRA, and concussion risk. Post hoc comparisons were completed using least squares means to compare shell add-on and impactor add-on across conditions.

Results, Conclusions, and Discussions:: Impact speed and location had a large effect on PLA, PRA, and concussion risk across all impact conditions (all p < 0.001). Both single and double add-on had meaningful effects on PLA, PRA, and concussion risk across all impact conditions; however, the response varied by add-on product (Table 1).

Concussion risk varied by impact speed (Figure 2). At lower speeds (2.3 and 3.4 m/s), risk was ≤ 2% across all impact conditions, however, at 4.9 m/s, concussion risk was 18% [Control: confidence interval (CI) 15-22%; Single add-on: 16-20%, p = 0.002; Double add-on: 16-20%, p = 0.012] prompting further analysis to focus on high-speed results. At this speed, both single and double add-ons influenced PLA, PRA, and risk, again varying by shell add-on product (Table 1), with the greatest reduction shown in the double Guardian Cap XT condition and the greatest increase shown in the double SAFR condition.

Helmet model also influenced PLA, PRA, and concussion risk (Figure 2). For the VICIS helmet, the single Guardian Cap XT produced the largest percent reduction in concussion risk, however, the magnitude was small. The double add-on condition was less effective at reducing concussion risk, due to an increase in PRA and decrease in PLA, likely due to changes in eccentricity. The Riddell helmet with the single Guardian Cap XT showed a slight increase in concussion risk due to an increase in PLA and PRA. However, the double Guardian Cap XT and single SAFR showed a decrease in concussion risk due to decreased PRA. Conversely, the double SAFR condition caused an increase in concussion risk due to an increase in PLA. For the Xenith helmet, both the Guardian Cap XT and SAFR products resulted in decreased concussion risk for both the single and double add-on conditions.

Overlap in 95% CIs for PLA, PRA, and concussion risk was common for most impact conditions, regardless of helmet model and add-on (Figure 2). This variability, coupled with instances of increased head accelerations, suggests that current add-on products may not be fully optimized for youth football impacts.

Acknowledgements and/or References (Optional)::