Several studies have reported that bicycle helmets tend to increase rotational acceleration in an accident, increasing the risk of brain injury.
A study funded by the Australian government set up unrealistic conditions where rotational acceleration is low. The study results are then arbitrarily generalized to all helmets in all conditions. This is deceitful, as the study unrealistic conditions are not representative of real life accidents.
An interview with an author of this study revealed that the study was not set up to address rotational acceleration, that soft-shell helmets are for cosmetic purposes, not really for protection, and that current helmets do not appear to protect against brain injury.
What causes brain injury?
We used to believe that brain injury is caused by a direct hit the head, like a head hitting a wall, causing linear acceleration. This is called focal brain injury, as it is focused on a particular area where the skull has been hit. However, scientific research done in the 1970′s has revealed that the main cause of severe brain injury is not focal injury but diffuse axonal injury:
“Protecting the brain from injury that results in death or chronic disablement provides the main motivation for wearing helmets. Their design has been driven by the development of synthetic polystyrene foams which can reduce the linear acceleration resulting from direct impact to the head, but scientific research shows that angular acceleration from oblique impulse is a more important cause of brain injury. Helmets are not tested for capacity to reduce it and, as Australian research first showed, they may increase it.“
Rotational acceleration means the head turning quickly. This quick rotation can create shearing inside the brain, tearing apart brain tissue and severing critical neural connections. This severe brain injury is called diffuse axonal injury. It can lead to permanent disability, when people have trouble operating normally, like in a vegetative state. This article reports from a surgeon who operates on cyclists:
” “The ones with brain swelling, that’s diffuse axonal injury, and that’s bad news” …
the whole brain is shaken up, creating many little tears in its inner structure …
Such patients undergo personality change, can contract epilepsy and have difficulty controlling their anger. They might become unemployable. Depression is a common accompaniment to brain injury. Rosenfeld sees patients’ families shattered, too. “They’re never the same. It often leads to marriage disharmony and family breakdown.” …
Rosenfeld’s opinion is candid. “I don’t know if [helmets] do much to protect the inner part of the brain,” “
Rotational acceleration is different from linear acceleration, which occurs when a moving object hits an obstacle, like a head hitting a wall. Helmets are designed to protect against low levels of linear acceleration, for impacts below 20 km/h. However, they are not designed to protect against rotational acceleration.
Helmets cannot protect against rotational injury but they can increase it, according to research done in Sweden:
“The non-shell helmet did in all trials grab the asphalt surface, which rotated the head together with
the helmet. The consequences were in addition to the rotating of the head, a heavily bent and compressed neck, transmitted on through the whole test dummy body after the impact. …
This gives an average angular acceleration of 20800 rad/s² for rotating the head from 0 to 0.26 rad during the 5 ms. Löwenhielm proposes 4500 rad/s² to be the maximum angular acceleration that can be tolerated for a limited time period, which also is suggested by Gilchrist and Mills.”
Soft-shell helmets are helmets without a hard shell. They are the most common type of bicycle helmet. Most have a thin layer of plastic on top, less than 1 mm thick.
The study found that soft-shell helmets grabbed the road surface, and then amplified rotational acceleration to four times higher than the tolerable maximum.
On impact, the larger head volume amplifies rotational acceleration. A study done in the UK reports that a difference of just 3cm in helmet circumference increases rotational acceleration by 150%:
“the 3000rad/s² to 8500rad/s² measured during abrasive and projection oblique tests with size 54cm (E) helmeted headforms. However, for the most severe cases using a size 57cm (J) headform, rotational acceleration was typically greater than 10,000rad/s² and increased to levels of 20,000rad/s², a level at which a 35% – 50% risk of serious AIS3+ injuries is anticipated.”
The difference between a helmeted and non-helmeted head is about 20cm.
This risk has been reported by other studies. In 1987, the Federal Office of Road Safety (FORS), an Australian government agency, completed research on helmets that highlighted several serious deficiencies with bicycle helmets:
“The substantial elastic deformation of the child head that can occur during impact can result in quite extensive diffuse brain damage. It is quite apparent that the liner material in children’s bicycle helmets is far too stiff …
rotational accelerations were found to be 30% higher than those found in similar tests using a full face polymer motorcycle helmet. More work needs to be done in this area as there would seem to be a deficiency in rotational acceleration attenuation that may be the result of insufficient shell stiffness ….
a high proportion of impacts were to the lover facial and side of face areas and it is imperative that the temporal area be more fully protected than it is by current bicycle helmet designs. “
This risk is not easy to isolate in real life, as there are often other contributing factors. However, a doctor from New Zealand reports that helmets convert what would have been focal head injuries into much more debilitating brain injuries:
“cycle helmets were turning what would have been focal head injuries, perhaps with an associated skull fracture, into much more debilitating global head injuries”
This is consistent with Canadian data that shows the length of stay in hospital increased following helmet laws, from 4.3 days to 6.9 days, suggesting more severe head injuries. In addition, the number of serious head injury admissions increased by 46% from 2000-2001 to 2003-2004.
A very strange “study”
Bicycle helmets are often presented as preventing brain injury, even though they are more likely to aggravate it. Making mandatory a device that can aggravate brain injury can have serious implications.
The Australian government introduced a policy of mandatory helmets despite being warned of this risk by its own researchers. Since then, it has not only failed to warn the public of this risk, but also attempted to deny it.
Many people wrote to the government about bicycle helmets, mentioning the risk of brain injury from rotational acceleration. Suddenly, the government had an answer to this concern, claiming:
“A 2009 study by the University of NSW confirmed the effectiveness of a bicycle helmet in reducing angular acceleration and subsequent brain injury in crashes”.
This study was not published in any scientific journal and could not be found anywhere. After much insistence, a copy was obtained from the Roads & Traffic Authority, a government agency. This study was commissioned and primarily funded by the Australian government. The abstract states that the study’s aim is to
“investigate the ability of a bicycle helmet to reduce angular head acceleration“.
It seems to be a “study” with a pre-determined conclusion, like this one.
The study was set with unrealistic conditions, by
- Using a type of hard-shell helmet not representative of the most common type of helmet used
- Testing at unrealistically low speeds of 5 to 11 km/h
- Testing on a non-abrasive surface not representing standard road conditions
- Failing to test for oblique impacts
Other studies have reported high rotational acceleration with soft-shell helmets, at speeds above 30 km/h, on a standard road surface, a more realistic setup. Oblique impacts tend to be the impacts generating high rotational acceleration. This study set up minimized the likelihood of encountering rotational acceleration, which is supposed to be the object of the study.
The study used a helmet with a ABS shell, like the one shown on the right, then arbitrarily generalised its results to all bicycle helmets, including the soft-shell helmet, the most common helmet today.
The study conclusion makes no mention of the unrealistically low speeds (5 km/h to 11 km/h) chosen. How can any serious accident protection research only do tests a low speed? It is well known that speed is a major factor affecting the severity of an impact. Testing only a low, unrealistic speeds is almost useless.
The conclusion fails to qualify the results by mentioning it was not using a realistic road surface. The flat surface used reduces the risk of the helmet sticking to the surface on impact. On a road, the polystyrene helmet would have most likely stuck to the road and generated high rotational acceleration, as reported by other studies.
Despite the unrealistic conditions, the study results are generalized without qualifications or justification. The study claims that
“At worst bicycle helmets do not appear to exacerbate head injury risks arising from angular acceleration.”
This is deceitful, as this “conclusion” is the result of the peculiar set up of the study, that cannot be generalised beyond the laboratory rather unusual conditions.
Interview with an author of the study
To better understand the circumstances behind this study, CRAG has interviewed one of the study authors. Here is an extract from this interview:
Why use hard-shell helmets?
“The helmets were supplied to us”
Why not use a soft-shell helmet, the most common type used today?
” the soft-shell helmet doesn’t do much – basically for cosmetic purposes – falls to pieces very easily - When touched can dent easily - Main function of soft shell helmets to ‘retain foam in semi-rigid format,’ not really for protection
Carbon fibre helmet (often used in motorcycle helmets) offers more protection but weighs more and deemed too heavy for bicycle riders – therefore not used in bicycle helmets”
The tests were done at speed from 5 km/h to 11 km/h. Why not higher speeds like 20 km/h?
“We had borrowed the RTA’s crash dummy and didn’t want to damage it”
Why use a flat surface and not a road surface?
“Time constraints at the time but did recognise need to replicate road conditions”
Do you believe that the conditions used in the study are realistic of real-world conditions?
The study concludes that helmets do not increase rotational acceleration, yet it doesn’t mention the context of study. Are you sure that this study is comprehensive enough to assert that, any helmet, in any situation, does not increase rotational acceleration?
“the study does not address any oblique impact issues so therefore does not address potential increase in rotational acceleration of the brain
… current helmets on the market are limited in preventing rotational acceleration
… there is no rotational testing element in the helmet standard. the current test method in the AUS/NZ standard is only related to linear injuries and only needs to pass a linear test. The current AUS/NZ standard does not include a rotational acceleration test”
Why isn’t the conclusion of the study qualified within the bounds of the experiment?
“within the limitations of the study, the conclusion raised that there is a risk of another possible head injury
… current helmets are only tested for linear injuries
In your opinion as an expert, do helmets do their job?
“As long as there is no oblique impact, yes
… But in an accident with any oblique impact, probably not
.. Current helmets do not appear to protect for brain injury such as concussion or haematoma“
There is a strange discrepancy between the study bold claim that helmets do not increase head injury through rotational acceleration, and the admission that the study did not include any oblique impacts, therefore could not assess rotational acceleration.
I wonder whether this researcher is aware that the study he participated in is being used to promote soft-shell helmets, that he admits are for “cosmetic purposes, not really for protection”.
Is this research or is this disinformation? This study still hasn’t been published in a scientific journal, escaping scrutiny from independent researchers. Its purpose seems to be to defend a controversial government policy, like other policy-driven studies. It seems a deceitful attempt to deny that helmets can aggravate brain injury.
The government is expected to fund research that can lead to better helmets, like it did in 1987 (before the helmet law). Commissioning research to mask the deficiencies of a government policy is deceitful. If a private company was caught commissioning fake research to cover up deficiencies in its product, there would be an outrage, with the government punishing the company heavily.
The primary task of public servants is to give honest and impartial advice, NOT to cover up their previous mistakes. When they engage in misleading and deceptive conduct, who is there to keep them honest?
How can using public funds to deceive the public be justified?
July 2013 update
The same team of researchers published a related study in 2013, entitled: “Bicycle helmets: head impact dynamics in helmeted and unhelmeted oblique impact tests“. It is is based on the flawed study described above.
Like the “study” described above, this later study sets up unrealistic conditions. Nothing can be concluded about real life accidents from such unrealistic conditions.
This study has already been peddled by helmet fanatics and bureaucrats as “proof” that bicycle helmets reduce rotational acceleration. Public money well spent?