The influence of repeated chin bar impacts on the protective properties of full-face mountain biking helmets

Full-face helmets are designed to protect against head and face injuries during downhill and free-ride mountain biking. This study assessed whether multiple impacts and helmet type are related to the protective properties of full-face helmets. A drop tower fitted with a helmeted headform simulated impacts to the chin following a forwards fall. Four models of full-face mountain biking helmets were tested. Three repeated trials were completed for each helmet at four impact velocities. Outcome variables included head injury criterion score, peak force, and peak acceleration. Peak accelerations for all trials were below the 300 g pass/fail criterion used in some testing standards. Multiple impacts reduced helmet protective properties, most noticeably at the higher impact velocities (increases in impact severity measures ranging from 11% to 22% for low and 17% to 49% for higher impact velocities). However, the effects of multiple impacts were smaller than the differences observed across individual helmet types. Helmet protective properties were associated with local chin bar characteristics, most notably chin bar length at higher impact velocities. Towards the goal of reducing overall head/brain injury risk in cyclists, there may be value in complimentary messaging about the importance of repeated impacts and helmet type on the protective properties of downhill mountain biking helmets.