Impact Sensors for Helmets
Summary: Many brands of impact sensors are being sold to be added to helmets to detect hard impacts. They have limited
usefulness for bicycle helmets, and limited accuracy at best. Most measure blows to the helmet, not the g's the head
inside experienced after the helmet's energy management. The biggest risk is that they will fail to signal a concussive
event or fail to signal damage to the helmet. Researchers believe they can signal hard impacts but can not diagnose
concussions. They are primarily useful in multi-impact sports for tracking sub-concussive blows.
We recommend reading
this cautionary announcement from the FDA "warning the public not to use medical devices marketed to consumers that
claim to help assess, diagnose or manage head injury, including concussion, traumatic brain injury (TBI) or mild
Impact sensors (usually accelerometers) attached to football players' heads made news about 2005, and devices to attach
to helmets have been marketed by a number of companies since.
A sensor attached to a helmet can only record the g's that the helmet sees, not what the head inside experienced. Since
the helmet is managing the energy, there will be a huge difference, with the head seeing far less shock. The original Simbex HIT system
for football players mounts an array of
accelerometers against the player's head, not on the outside shell of the helmet.
Accelerometers are linear, registering g's in only one direction. To capture all of the energy in an impact, seven is the
minimum number of accelerometers to use, oriented in different planes. Eleven would be more accurate. Most of the devices
marketed now use only one accelerometer, or at most three.
The Simbex product uses multiple accelerometers held against the head, and gathers the data on the sidelines of a game
through a wireless connection. It works, and can alert the coach when a player takes a very hard hit. Simbex and the
college football researchers using the system have gathered millions of hits in their data collecting. But correlating
the hits and concussions has proven elusive. There is still no agreement on the exact profile of a concussive hit. Some
players have experienced 140 peak g's without an injury that can be diagnosed clinically. Some have been concussed at
levels below 80 g's. Results vary depending on the direction of the blow, area of the impact and other factors. There is
no precise way yet to define the characteristics of the hit that produces a concussion. Peak g has to be important, and
rotational energy is believed to be another key element. Even a straight linear hit involves some rotational component.
But what is happening inside the head as the brain moves, as different brain components with different densities and
placement move in different ways, contributes to the nerve and blood vessel strain that is thought to be a big
determinant of concussion. Simbex says their system is best used by coaches to identify players who are experiencing many
hard hits and permit the coach to train that player to avoid them in the future.
Back in 2006 we bought some samples of a device called the Shok-SpotR and asked experts for an evaluation. The device is
designed to be added to a hard shell helmet, and registers g's above a certain level by turning a spot red. We got mixed
feedback from the lab techs and other experts, who saw it as a device to register helmet damage, since it did not
register g's to the head. Some felt that even assuming it functioned correctly, the spot might not change in some crashes
that would damage the helmet. Most believed that visual inspection and measuring for foam crush after a crash is the best
way to determine if a helmet has been damaged. But since many consumers are not experienced in looking at damaged helmets
and may not recognize damage under a shell, there may still be a place for this product if you wear a helmet with a rigid
hard shell. Our samples were $25 plus shipping, from a supplier we found with Google.
As concern about concussions has grown in recent years other devices have come on the market, including Impact Alert,
Shockbox, the Stabilizer First Alert (attaches to a hockey face mask) and many others. There are also sensors with
electronics in a mouth guard. Those at least try to measure g's to the head, not the helmet, but must assume that the jaw
remains firmly clamped on the mouthguard through the impact sequence. We found all of those and more with
this Google search
. It will be more current than any list we post here would be. We know nothing of the effectiveness
of any of the devices except the Simbex HIT system, a reliable indicator of hits on a sports field.
In April of 2019 the US Food and Drug Administration (FDA) issued
a press release
"warning the public not to use medical devices marketed to consumers that claim to help assess,
diagnose or manage head injury, including concussion, traumatic brain injury (TBI) or mild TBI." The only devices the FDA
has cleared must be used by a health care professional, and "there are currently no devices to aid in assessing
concussion that should be used by consumers on their own." That is expert advice that none of us should ignore.
mid-2018 post on the web
by child athlete advocate Brooke de Lench represents a good review of the sensor field,
except that it does not distinguish between sensors mounted on a helmet and those mounted against the head. She does make
the point well that the sensors are primarily useful in multi-impact sports for tracking sub-concussive blows, not for
diagnosing a concussive impact.
In 2016 the F08.53 Helmet and Headgear subcommittee of ASTM began developing a standard for the performance of sensors
used to track head impacts. CPSC chairs the task group. The task group will have a difficult job, and the development of
the standard may take some time. There has not been much progress as of late-2020. But eventually you may be able to buy
an impact device with confidence that it meets a performance standard.
: many of the sensors are designed for use with hard shell helmets. Most will not tell you much about
how hard an impact your brain actually took or whether an injury has occurred. We do not know of a consumer product that
will tell you if you have a concussion, and for bike riders a medical diagnosis of the symptoms you are experiencing will
always be your best indicator. If you are crashing repeatedly and need to track the number of hits your helmet
experiences, there are products to do that.