Abstract
Bicycle helmets are shown to offer protection against head injuries. Rating methods and test standards are used to evaluate different helmet designs and safety performance. Both strain-based injury criteria obtained from finite element brain injury models and metrics derived from global kinematic responses can be used to evaluate helmet safety performance. Little is known about how different injury models or injury metrics would rank and rate different helmets. The objective of this study was to determine how eight brain models and eight metrics based on global kinematics rank and rate a large number of bicycle helmets (n=17) subjected to oblique impacts. The results showed that the ranking and rating are influenced by the choice of model and metric. Kendall’s tau varied between 0.50 and 0.95 when the ranking was based on maximum principal strain from brain models. One specific helmet was rated as 2-star when using one brain model but as 4-star by another model. This could cause confusion for consumers rather than inform them of the relative safety performance of a helmet. Therefore, we suggest that the biomechanics community should create a norm or recommendation for future ranking and rating methods.
Highlights
Head injuries are a significant problem in society that can cause both acute and long-term consequences
Bicycle helmets have been shown to mitigate the severity of injury during head impacts by reducing the forces acting on the head.[8,9,15,37]
A variation of Maximum Principle Strain (MPS) and Cumulative Strain Damage Metric (CSDM) is seen between the different models (Figure 2)
Summary
Head injuries are a significant problem in society that can cause both acute and long-term consequences. The head is the most common body region for severe injuries among bicyclists.[41]. Bicycle helmets have been shown to mitigate the severity of injury during head impacts by reducing the forces acting on the head.[8,9,15,37] In most countries, helmets need to pass a specific certification standard to be allowed into the market. Most helmet test standards evaluate a helmet’s safety performance using only the measured linear acceleration of a dummy headform resulting from impacts against a rigid surface, e.g., a flat surface or a curbstone. In the current bicycle helmet standards,[1,7,13] the pass/fail threshold for a helmet ranges between 250 and 300 g peak linear acceleration, depending on the standard
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