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

Abstract

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.

Impact attenuation provided by older adult protective headwear products during simulated fall-related head impacts

“…As described previously, 24 a mechanical impact simulator (drop tower) was used to impact a medium-sized Hybrid III (HIII) headform onto a uniaxial load cell mounted beneath an impact anvil (Model 925M113; Kistler Instrument Corporation, Amherst, NY, USA) ( Figure 2 ). HIII headforms have previously been used in experiments comparing unhelmeted and helmeted head impacts, 28 , 35 and have the benefit of being more resilient against damage during baseline impacts compared to other headforms. Impact velocity was measured with an infrared light gate velocimeter (Model VS300, GHI Systems, Aurora, ON, Canada) positioned immediately above the impact surface.…”

“…47 Future studies may consider employing a range of impact velocities towards characterizing potential velocity-dependencies in the protective capacity of the products. Third, while the test system employed was similar to those reported in the literature, 28,35 the lack of a surrogate neck increased system stiffness. While this likely contributed to the relatively high g max values we observed, it is unlikely the relative ranking of PHPs was affected.…”