Helmet Stability and Fit in Australian Pedal and Motor Cyclist Populations

Background. The ability of a pedalor motor-cycle helmet to reduce injury to the wearer in the first instance depends on its stability and retention. A helmet may be displaced or even ejected if it has been incorrectly fastened, worn, or inappropriately sized for the wearer's head. Current helmet test standards include a stability test to evaluate the sizing and likelihood of roll-off by applying static or dynamic loads to the helmet when fastened to a standard headform. The relationship between helmet performance tests and helmet stability on rider populations has not been assessed. Objectives. The main objectives of this study were (1) to assess pedaland motor-cycle helmet stability and fit in a user population and (2) to assess the appropriateness of the current helmet stability test methods. Methods. Pedaland motor-cyclists of various ages, backgrounds and abilities were surveyed over a 3 month period within the Sydney metropolitan area. Anthropometric, demographic and cycling data were collected. Details of the cyclist's helmet were recorded. To assess stability a static pull force was applied to the helmet in situ and as worn by the cyclist. The force required to displace the helmet and the extent of displacement were measured. For some helmets that were loosely worn, the test was repeated after readjustment of the helmet straps. Results. 269 participants were recruited for the study, yielding 255 usable case data (128 pedal cyclists and 127 motorcyclists). The age range of pedal cyclists surveyed was 4 to 68 years (median 21 years). For motorcyclists, the age range was 20 to 69 years (median of 46 years). Pedal cyclist head circumference ranged from 50 to 62.5cm (median 56cm) and motorcyclists ranged from 53 to 64.5cm (median 58cm). It was found that 55% of pedal cyclists chose the correct helmet size for their head circumference, compared to 40% of motorcyclists. However, 60% of pedal cyclists wore their helmet incorrectly compared with 10% of motorcyclists. Most helmets (97%) worn met standards that include a stability test. Differences between head dimensions and equivalent headform dimensions of up to 60mm were measured. It was found that an average static load of approximately 6N was required to displace the pedal cycle helmets by 10 degrees in any direction. For full-face motorcycle helmets, this load was 30N and 18N for open-face motorcycle helmets. Conclusions. In this first survey on this topic, it was observed that up to half of helmet users may be wearing inappropriate helmets for their head size and shape, and that helmet misuse was high, particularly among pedal cyclists. Although most of the helmets worn have passed stability tests, stability in situ was of concern. It was shown that it was easy to displace helmets on user's heads with a static load. This is of particular concern for pedal cycle helmets offering minimal head coverage, where any displacement can expose the cranium to direct impact in a crash.