How Well Do Popular Bicycle Helmets Protect from Different Types of Head Injury?
Bicycle helmets are designed to protect against skull fractures and associated focal brain injuries, driven by helmet standards. Another type of head injury seen in injured cyclists is diffuse brain injuries, but little is known about the protection provided by bicycle helmets against these injuries. Here, we examine the performance of modern bicycle helmets in preventing diffuse injuries and skull fractures under impact conditions that represent a range of real-world incidents. We also investigate the effects of helmet technology, price, and mass on protection against these pathologies. 30 most popular helmets among UK cyclists were purchased within 9.99–135.00 GBP price range. Helmets were tested under oblique impacts onto a 45° anvil at 6.5 m/s impact speed and four locations, front, rear, side, and front-side. A new headform, which better represents the average human head’s mass, moments of inertia and coefficient of friction than any other available headforms, was used. We determined peak linear acceleration (PLA), peak rotational acceleration (PRA), peak rotational velocity (PRV), and BrIC. We also determined the risk of skull fractures based on PLA (linear risk), risk of diffuse brain injuries based on BrIC (rotational risk), and their mean (overall risk). Our results show large variation in head kinematics: PLA (80–213 g), PRV (8.5–29.9 rad/s), PRA (1.6–9.7 krad/s2), and BrIC (0.17–0.65). The overall risk varied considerably with a 2.25 ratio between the least and most protective helmet. This ratio was 1.76 for the linear and 4.21 for the rotational risk. Nine best performing helmets were equipped with the rotation management technology MIPS, but not all helmets equipped with MIPS were among the best performing helmets. Our comparison of three tested helmets which have MIPS and no-MIPS versions showed that MIPS reduced rotational kinematics, but not linear kinematics. We found no significant effect of helmet price on exposure-adjusted injury risks. We found that larger helmet mass was associated with higher linear risk. This study highlights the need for a holistic approach, including both rotational and linear head injury metrics and risks, in helmet design and testing. It also highlights the need for providing information about helmet safety to consumers to help them make an informed choice.
Cycling is an active mode of mobility with significant health and environmental benefits. In England, there has been a significant upward trend in cycling since 2002 [1]. Despite many health, environmental, and independent travel benefits, there can be a risk of trauma in bicycle falls and collisions. In Great Britain, cyclists had a reduction in fatalities in 2021 (down 21%) compared with a significant peak during the 2020 COVID-19 pandemic. Despite this reduction, cyclist fatalities in 2021 remained higher than the 2017 to 2019 average (increase of 17%) [2]. Head injuries are a key cause of fatal and life-changing injuries in cyclists [3]. Some cyclists choose to wear a helmet as a key line of defense against head injuries if they are involved in a collision or fall. Several previous studies, including a large meta-analysis of data relating to 64,000 cyclists, have shown that helmets have a protective effect to the head against head injury (including serious and fatal injury) and facial injury in cycle incidents, such as collisions and falls [3, 4]. In particular, helmet use has been found to reduce the risk of skull fractures, hemorrhages (extradural, subdural, subarachnoid, intraparenchymal, and intraventricular) and facial fractures when a cyclist is involved in a collision or fall event [5,6,7,8,9,10,11,12,13].
