Effects of external helmet accessories on biomechanical measures of head injury risk: An ATD study using the HYBRIDIII headform.

Competitive cycling is a popular activity in North America for which injuries to the head account for the majority of hospitalizations and fatalities. In cycling, use of helmet accessories (e.g. cameras) has become widespread. As a consequence, standards organizations and the popular media are discussing the role these accessories could play in altering helmet efficacy and head injury risk. We conducted impacts to a helmeted anthropomorphic headform, with and without camera accessories, at speeds of 4m/s and 6m/s, and measured head accelerations, forces on the head-form skull, and used the Simulated Injury Monitor to estimate brain tissue strain. The presence of the camera reduced peak linear head acceleration (51% - 4m/s impacts, 61% - 6m/s, p<0.05). Skull fracture risk based on kinematics was always less than 1%. For 4m/s impacts, peak angular accelerations were lower (47%, p<0.05), as were peak angular velocities (14%) with the velocity effect approaching significance (p=0.06), with the camera accessory. For 6m/s impacts, accelerations were on average higher (5%, p>0.05) as were velocities (77%, p<0.05). Skull forces were never greater than 443.2N, well below forces associated with fracture. Brain tissue strain, the cumulative strain damage measure at 25% (CSDM-25), was lower (56%, p<0.05) in 4m/s but higher (125%, p>0.05) in 6m/s impacts with the camera accessory. Based on CSDM-25 for 4m/s tests, the risk of severe concussion was reduced (p<0.05) from 25% (no camera) to 7% (camera). For 6m/s tests, risks were on average increased (p>0.05) from 18% (no camera) to 58% (camera).