May 21, 2022

Understanding science

Do helmets give cyclists a false sense of security?

PedalMe, a London-based e-bike company, recently announced that their employees were not allowed to wear bike helmets for safety reasons. Does their rationale have any merit?

Read Time 5 minutes

It is well established that wearing a bike helmet reduces the chance of severe head injury in the case of a crash, and new developments in helmet technology only further reduce the likelihood of traumatic brain injuries. But a cargo e-bike company, PedalMe Bikes, recently caught a lot of attention for announcing that their drivers are not allowed to wear helmets, and that anyone who wants to wear a helmet is not welcome to work for them.

Do helmets encourage us to take more risks?

The London-based company claimed that while helmets are protective in the event of a crash, riders who wear helmets take greater risks due to a false sense of security. This rationale, called risk compensation theory, is the same reasoning that has been applied to arguments about guardrails on mountain roads and child safety caps on medication. The basic premise is that safety measures will cause the public to behave more recklessly (e.g., driving faster on winding mountain roads or carelessly leaving medication around young children).

Does this theory have any merit in the case of bike helmets? A 2019 systematic review of studies on exactly this hypothesis found little to no evidence supporting the claim, and more strongly found evidence for quite the opposite: cyclists who wore helmets often displayed safer behavior. For example, cyclists who regularly wore helmets were found to have higher perceived risk of injury, lower risk for crash injury, and decreased crash fault. There was also no association found between helmet wearing and increased cycling speed. It should be noted that none of these studies were able to control for the possibility that people who are inclined to wear helmets of their own volition may be naturally more biased toward cautious behavior, which is a very important confounder.

Only two of the twenty-three included studies suggested elevated risks for cyclists wearing helmets. One of these two studies that supported risk compensation theory didn’t actually test cycling behavior; this laboratory study evaluated risk-taking and sensation-seeking while the participant was wearing either a bike helmet or a baseball cap. Participants performed a repeated task that required clicking to inflate an animated balloon and earning fictional money for each click. When wearing a bike helmet, participants were more likely to engage in “risky” behavior – continuing to inflate the balloon instead of “banking” the fictional money at a more conservative time point. And if this scenario seems contrived and ridiculous to you, then it is only logical to give more weight to the studies that did not support risk compensation theory when evaluating biking in the field.

One reason risk compensation theory may not hold up in real-world scenarios is that cyclists likely account for risks beyond head injuries alone when decision-making. In 2019, there were an estimated 328,903 nonfatal emergency room visits due to cycling crashes. The most common cycling-related injuries include broken arms, broken collarbones, wrist injuries, and road rash, none of which are prevented by wearing a helmet. While not the most common injury, head injuries are among the most severe and most frequent causes of cycling-related fatalities, with an average of about 60,000 cycling-related traumatic brain injuries each year. A retrospective study of 6,267 patients with an intracranial hemorrhage after bicycle-related accidents found that the 25% of helmeted bicycle riders had reduced the odds of traumatic brain injury (TBI), mortality, and facial fractures by 51, 44, and 31 percent, respectively relative to non-helmeted riders.

How effective are helmets at reducing injury?

But even if helmeted cyclists don’t engage in riskier behavior, might there be other reasons to question the use of bike helmets? One argument is that they aren’t actually effective at protecting against brain injuries. Head injury criterion (HIC) is a measure of the likelihood of head injury arising from the accelerations of an impact. A study that measured HIC using drop tests for helmeted and unhelmeted dummy headforms found that at modest impact speeds (12 mph), the unhelmeted headform experienced an HIC associated with a 99.9% risk of severe brain injury. This risk was reduced to 9.3% when the headform was helmeted – more than a ten-fold reduction in risk of severe brain injury. Empirical evidence and retrospective crash reviews overwhelmingly support that helmets are very effective at reducing bike crash-related brain injury risk.

This isn’t to say helmets offer unlimited protection. Typically, the most severe cycling accidents are those that involve motor vehicles, and in such cases, often no amount of protective gear could be sufficient to avoid fatality. Whether or not you’re wearing a helmet won’t matter much if a 2-ton SUV t-bones your bicycle at 50 mph. This may explain why, in contrast to TBI risk, wearing a helmet does not appear to have a major impact on reducing risk of cycling fatality: among cyclists involved in fatal accidents, the percentage who had worn helmets is comparable to the percentage of helmet-wearing cyclists in general. In other words, of the 843 cycling fatalities recorded in 2019, we see only a modest bias toward those who were not wearing helmets. So although helmets reduce the likelihood of injury in many circumstances, it is worth noting that they do not impart absolute invulnerability.

Reducing the risk of head injury on impact does require that the helmet be fitted properly. The outer shell and foam of the helmet are designed to absorb and dissipate the energy of impact, but gaps can cause a loose-fitting helmet to move out of place and also allow the head to accelerate before it hits the energy-absorbing liner, thus increasing the likelihood of a head injury. Soft-fitting pads added to the helmet’s interior are not sufficient to make up for these gaps because they are ineffective at absorbing the energy of impact, so the head will still accelerate. Likewise, hairstyles such as braids will have a similar effect as soft-fitting pads and can make proper helmet fitting more difficult. According to one study, children who had been in a crash were nearly twice as likely to have a head injury if they had been wearing a poor-fitting helmet than if they had been wearing a well-fitted helmet.

One cause for concern is counterfeit helmets – helmets sold on some e-commerce sites that often look like brand-name versions and even have fake stickers indicating that the helmet meets certain safety standards. While counterfeit helmets look very similar to their authentic counterparts, they usually weigh less due to the absence of some of the internal structural elements. When put through the same testing, the counterfeit versions fail most, if not all, safety tests, meaning they offer none of the same protections as genuine helmets. For the individual rider, the best way to ensure a helmet meets safety standards is to buy from a local bike shop or directly from a bike manufacturer and always check for a CPSC safety sticker inside the helmet.

The bottom line.

Cycling is increasing in popularity for exercise, recreation, transportation, or in the case of PedalMe Bikes, employment. Like most physical activities, cycling comes with some inherent risks, but helmets have been repeatedly shown to mitigate traumatic brain injuries from crashes. A company should not be able to mandate (or base their hiring practices on) a policy that their employees must not wear a bike helmet while on the job. Though the protection afforded by helmets does have limitations, one thing is clear: scientific evidence does not support the risk compensation theory for PedalMe’s anti-helmet mandate and reveals their policy for what it truly is: careless at best, and at worst, an accident waiting to happen.

Disclaimer: This blog is for general informational purposes only and does not constitute the practice of medicine, nursing or other professional health care services, including the giving of medical advice, and no doctor/patient relationship is formed. The use of information on this blog or materials linked from this blog is at the user's own risk. The content of this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Users should not disregard, or delay in obtaining, medical advice for any medical condition they may have, and should seek the assistance of their health care professionals for any such conditions.
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