A Comparison Between Two Oblique Test Protocols for Cycling Helmets

Abstract

Based on accident reports, oblique head impacts associated with rotational acceleration occur frequently in cycling. Rotational acceleration stimulates brain tissue strain resulting in mild to severe brain injuries. Current bicycle helmet standards test for linear acceleration, but not for rotational acceleration. The proposed standard (EN13087-11) by the European Committee for Standardization (CEN) and the Angular Launched Impact (ALI) protocol are oblique test protocols which impart rotational acceleration to the head at three impact locations (Front_Y, Lateral_X and Lateral_Z). The CEN proposed standard drops the helmeted headform vertically onto a 45° steel anvil, while the ALI protocol launches the headform at an angle of 45° towards the steel surface. The CEN proposed standard may represent a cyclist falling vertically onto a curb, angled surface or motor vehicle. The ALI represents a cyclist skidding or falling over the handlebars and have been described as frequent-accident cases in the literature. Both protocols represent unique falling events in cycling which elicit distinct rotational head responses. The purpose of this study was to compare the dynamic head response and brain tissue deformation between the two oblique test protocols on two common types of cycling helmets (PVC shell-PU liner and ABS shell-EPS liner). The study revealed that falling vertically onto a curb, angled surface or motor vehicle (CEN proposed standard), resulted in a greater rotational head response and brain tissue deformation, compared to frequent-accident events of skidding or falling over the handlebars (ALI protocol). Linear and rotational acceleration were significantly less on the PVC shell-PU liner compared to the ABS shell-EPS liner on both oblique test protocols. Distinct impact vectors associated with unique falling events in cycling create different rotational head responses and brain tissue deformation. Helmet standards should consider incorporating oblique testing methods, to manage mild and severe brain injuries associated with frequent falling events in cycling.