The current design of bicycle helmets entails an EPS (expanded polystyrene) liner with fixed a hard plastic outer shell cover. The EPS liner is the primary protective design feature that crushes and absorbs the impact energy. Ultimately, the EPS liner reduces the energy transmitted to the skull and brain, thereby reducing the risk of injury. The hard shell feature helps prevent the helmet from snagging on the pavement and inducing neck injuries in addition to distributing the impact force over a wider area.
Head and specifically brain injuries are not solely due to a direct linear type of impact. Brain injuries, including concussions, also occur from excessive angular acceleration. In other words, the head can be suddenly rotated during an accident, causing injuries to the brain tissue. Some bicycle helmet manufactures have designed helmets to better manage the angular acceleration during an impact and have termed their helmets as “MIPS (Multi-directional Impact Protection)”, “AIM (Angular Impact Mitigation)”, or “ODS (Omni-Directional Suspension)”. These helmets are designed with the standard hard plastic outer shell and also have an inner type of shell connected to it with a type of energy management system that functions to manage the rotational acceleration of the head.
All bicycle helmets sold in the United States must meet minimum safety standards set by the CPSC (Consumer Product Safety Commission). At this point, the current bicycle helmet testing standard addresses only the direct linear impact type of scenario. Research is being conducted throughout the US to better understand the injury mechanism associated with angular acceleration. Ultimately, this information will be used to develop new and better bicycle helmet safety standards.
TIMOTHY JOGANICH, MSES , C.H.F.P. is an ARCCA expert with more than 20 years’ experience in the sciences of human movement, biomechanics and human factors. He specializes in the analysis of bicycle accidents, based on his educational background and his own personal and extensive cycling experience, including competitive racing, touring, fitness/recreational riding, commuting and coaching.