By: Reanne Li
Original Article: Cripton, P.A., Dressler, D.M., Stuart, C.A., Dennison, C.R., Richards, D. (2014). Bicycle helmets are highly effective at preventing head injury during head impact: Head-form accelerations and injury criteria for helmeted and unhelmeted impacts. Accident Analysis and Prevention, 70, 1–7. Find the original article here.
Cycling is a widely popular activity; however, it is also one of the principal causes of summer sports-related head injuries. Bicycle helmets are a traditional method of prevention. Several epidemiological studies conducted across the world report that certified bicycle helmets significantly reduce the risk of head injury relative to un-helmeted impacts. However, critics discount the accuracy of these studies on the basis of study design. There are also some epidemiological studies that show helmets do little to prevent head injuries. These epidemiological studies are always difficult because there is no way to know how hard a person hit their head or even if they hit their head in a particular bicycle crash. Furthermore, standard helmet laboratory impact testing is often done with head forms that cannot be used for testing without a helmet and thus there are very few studies, and none in the peer-reviewed literature, that show how effective a helmet is when compared to a similar head impact with no helmet
To address the critics’ concern, the researchers of this study designed a biomechanical experiment to measure helmet efficacy to reduce head injury during impacts similar to real-world accidents. The researchers used a Hybrid III crash test dummy head-form that could withstand un-helmeted impacts, and a certified bicycle helmet that met government safety standards. The researchers built a monorail drop tower. They dropped pairs of helmeted and un-helmeted head-forms onto a flat anvil from identical heights. To encompass a wide range of impacts similar to realistic bicycle accidents, the researchers performed a total of 18 drops from heights ranging from 0.5 to 3.0 metres. To ensure the validity of their data, the investigators performed multiple drops from two metres. The researchers measured the linear accelerations of the helmeted and un-helmeted head forms for each drop and calculated the velocity of impact using high-speed video. The peak head form acceleration and the subsequently calculated Head Injury Criterion (HIC) was used to quantify the likelihood of injury if a human had suffered the corresponding impact to that under study.
Most important finding:
The authors found that helmets reduced the risk of brain injury in each experimental condition. The risk was almost completely eliminated in falls of one metre and lowered by up to 35% in drop heights below two metres. However, the investigators concluded that helmets are not as useful in falls greater than three metres. The researchers determined that realistic bicycle accidents correspond to their experimental drop height of 1.5 metres. Based on this correlation, they concluded that a helmet would lower the chance of sustaining a skull fracture or life threatening brain injury from 99.9% to 9%.
Things to consider:
Cripton and team’s use of contemporary off-the-shelf bicycle helmets, realistic head models, and a wide range of impact velocities made their results more applicable to real-world cycling than those of previous studies. However, the head-forms are only a replica of the human skull. Furthermore, the drop height, impact location, mass of head-form, helmet model and helmet fit were all carefully monitored in the study. These variables are not as constant in real life and therefore, human skull behaviour during impact may deviate from the authors’ findings.
What does this mean for you?
This study suggests that in the case of a cycling accident, wearing a contemporary, certified bicycle helmet will significantly reduce the chance of sustaining a skull fracture or debilitating severe head injury.