Several studies have reported that bicycle helmets can increase rotational acceleration. Rotational acceleration is the primary cause of brain injury.
A study set up unrealistic conditions fostering low rotational acceleration. The study claims that helmets do not increase brain injury. This is deceitful. The study unrealistic conditions are not representative of real life accidents.
An interview with a study author revealed that the study was not set up to address rotational acceleration. The study author admitted:
soft-shell helmets are for cosmetic purposes, not really for protection, …
current helmets do not appear to protect against brain injury.
What causes brain injury?
An old popular belief is that brain injury is caused by a direct hit the head, like a head hitting a wall, causing linear acceleration. This is focal brain injury. Bicycle helmets are designed to reduce focal injury. The polystyrene reduces linear acceleration by compressing on impact.
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 can create shearing inside the brain, tearing apart brain tissue. This is diffuse axonal injury. It can lead to permanent disability. 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,” “
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.”
Soft-shell helmets amplified rotational acceleration to four times higher than the tolerable maximum. Soft-shell helmets are helmets without a hard shell. They are the most common type of bicycle helmet.
On impact, the larger head volume amplifies rotational acceleration. A 3cm increase 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.
In 1987, an Australian government agency released research that highlighted 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 doctor from New Zealand reports:
“cycle helmets were turning what would have been focal head injuries, perhaps with an associated skull fracture, into much more debilitating global head injuries”
In Canada, the length of stay in hospital increased increased following helmet laws, from 4.3 days to 6.9 days. The number of serious head injury admissions increased by 46%.
A strange “study”
The Australian government introduced a policy of mandatory helmets. Many people wrote to the government about brain injury from rotational acceleration. The bureaucrats claimed:
“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 commissioned by the government. It was not published. After much insistence, a copy was obtained from a government agency. 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 (Oblique impacts generate high rotational acceleration)
Studies have reported high rotational acceleration with soft-shell helmets, at speeds above 30 km/h. This study fostered low rotational acceleration.
The study used a helmet with a ABS shell, like the one on the right. Then it generalised its results to all bicycle helmets.
The study conclusion makes no mention of the unrealistically low speeds (5 km/h to 11 km/h). How can accident protection research only do tests a low speed? Speed is a major factor affecting impact severity. Testing only a low 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. Other studies have reported that helmets tend to stick to the road surface.
Despite the unrealistic conditions, the study claims are generalized without qualifications:
“At worst bicycle helmets do not appear to exacerbate head injury risks arising from angular acceleration.”
This is deceitful, as this claim is the result of the peculiar set up of the study. It cannot be generalised beyond the laboratory conditions.
Interview with an author of the study
CRAG has interviewed one of the study authors:
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”
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”
Do you believe that the conditions used in the study are realistic of real-world conditions?
Is this study comprehensive enough to assert that helmets do 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.”
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“
This study is still not published, escaping independent scrutiny. Its purpose seems to be to defend a controversial government policy.
The government is expected to fund research to improve helmets, like it did in 1987 (before the helmet law). Commissioning research to mask deficiencies of a government policy is unethical.
July 2013 update
The same team of researchers published a related study in 2013. It is called: “Bicycle helmets: head impact dynamics in helmeted and unhelmeted oblique impact tests“.
Like the “study” described above, this study sets up unrealistic conditions. Nothing can be concluded about real life accidents from unrealistic conditions.
Bureaucrats have peddled this study as “proof” that helmets reduce rotational acceleration.
Public money well spent?