Football helmet testing standards need rotational acceleration

An evaluation of football helmet testing standards with recommendations to include
rotational acceleration testing
To
Mike A. Shapiro
EPD 397
By
Molly Mentzer
Material Science and Engineering Department
University of Wisconsin-Madison
December 23, 2015

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Contents
Executive Summary……………………………………………………………………..…………………3
Introduction.………….……...….…..………………………….…………………………….……….……4
1.0 Concussions……………………………………………………………………………………….……..5
Concussions in sports………………………………………………………….….….….……..5
What concussions are……………………………………………….…………………….…….5
How concussions occur……………………………………..………………………………….5
Linear and rotational acceleration…………………………………………………….….6
Acceleration differentiation……………………………………………………..….……….6
Managing acceleration in sports……………………………………………………………7
2.0 Linear Acceleration Testing……………………………………………………..……………….7
Initial helmet testing………………………………………………………..…………………..8
Newly proposed linear acceleration testing……………………………...….….....10
Accuracyof linear acceleration testing………………………………….…….…...…13
3.0 STAR Methods Comparison………………………….………………………………….....….13
Comparison of head injuries in sports…………………………………………………13
4.0 Design Matrix ………….………………………………………………………………………………17
5.0 Conclusions.………………….……………………..…………….……………….………………….18
References…………………………………………………………………………………………………….20

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Executive Summary
The large number of concussions seen in sports has highly desensitized younger generations to the
impact of head injuries and development. Concussions occur when an impact causes the brain to
move in the skull, striking the inside of the skull and/or twisting. These injuries are the result of
both linear and rotational acceleration.
The primary protection against concussions are helmets that athletes wear during play. The
purpose of the football helmet is to reduce the acceleration of each impact, mitigating the injuries
sustained to the brain. Football helmet testing standards regulate how protective helmets are, but
currently only measure for linear acceleration. This technical report analyzes football helmet
testing standards for the best possible method to implement rotational acceleration into testing.
The most common methods of helmet testing are the linear drop test, linear impact test, and the
football and hockey (Summation of Tests for the Analysis of Risk STAR) methods.
 The liner drop test drops a helmet onto a stationary anvil at a single height.
 The linear impact tests strikes a helmet and head form, allowing it to move with inertia.
 The football STAR method tests the linear drop test at numerous different heights.
 The hockey STAR method uses a pendulum and adjustable base to strike helmets.
Using sources and studies published in the Journals of Biomedical Engineering, Clinical Sports
Related Medicine, and Sports Engineering and Technology,I evaluated the above 4 methods on
the criterion of head form type, neck type, acceleration equivalence, and angular hit directions.
My analysis shows that in terms of realistic impacts, the hockey STAR method is the most
versatile and comparable to impacts that occur during play.
In terms of realistic fit and neck response, the head form used in the linear drop test is the most
realistic relating to fit. For neck response, the non-rigid neck of the linear impact test allows the
head form to recoil naturally.
In terms of impact acceleration, the STAR methods are the only ones to test at multiple different
accelerations. Additionally, the pendulum set up for hockey STAR allows for an easy change in
acceleration of a test, making it versatile for testing average and maximum impact accelerations.
In terms of angular hits, the pendulum set up for hockey STAR is the only mechanism which
allows for rotational acceleration testing. All other testing methods are based solely on linear
acceleration.
In conclusion, I determined that for helmet testing to be the most accurate the choice of standard
testing depends on how realistic the testing methods are to impacts that occur during use. This
suggests that the best-fit head form and recoil neck should be used. The only method which
utilizes this degree of realism is the hockey STAR method.

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Introduction
An estimated 1.6-3.8 million sport concussions are reported each year in the United States [1].
Football is the sport associated with the largest number of traumatic brain injuries, but this is also
because it has the largest number of participants [1]. Because of the large number of concussions
seen in sports today, younger generations are desensitized to the affects that concussions and
repeated concussions have on the body. In the last 10 years, the number of concussions has
plateaued when it should be dropping [2].
To reduce concussions further,informative programs have been launched to create awareness of
their dangers. The Heads Up programs for youths helps them understand the risk of head impacts.
Case studies are being presented to college and professional players. Using real data makes them
more aware of long-term concussion effects [1]. The rules in football are also being adjusted to
ensure that the proper recovery is taken before returning to game play or practice.
These changes, though necessary, would be best impacted with improved studies in helmet testing
and those tests’ effectiveness in mitigating concussions. While there is no perfect helmet, the fact
is that helmets are not currently sufficient in diminishing the long term effects of concussions.
Current helmet testing use linear acceleration to determine if helmets are suitable for use during
practice and games. As found in tests done by the 1970’s National Operating Committee on
StandardsforAthleticEquipment(NOCSAE),linearacceleration alonewasnot sufficientin causing
a concussion [3]. Rotational acceleration testing, found in hockey helmet standards, tests helmets
for the kind of impacts that typically cause concussions. The purpose of this report is to find the
best method to integrate rotational acceleration into football helmet testing standards.
To know if rotational acceleration testing has the necessary protocol to increase the effectiveness
of helmets, this report provides an analysis through several steps:
 First, it analyzes what linear and rotational acceleration are and how they each effectively
act to cause a concussion from an impact.
 Second, it analyzes three methods used to measure and test linear acceleration: NOCSAE,
HIT, and Hybrid III. This technical background on methods will show that linear
acceleration is thoroughly tested for.
 Third, it explains the recently published STAR method for football and hockey. The
differences between their equations will be explained in addition to conclusions drawn
which optimize performance.
This report concludes, then, that the football STAR method should be modified to include the
rotational acceleration testing found in hockey STAR.

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1.0 Concussions: Who, What, Where, and Why
Concussions are extremely underrated injuries to the head that are common in most contact
sports.
Concussions in sports areprimarily seen in football because of the sport’s popularity.
The game of football has the greatest number of concussions of all sports in North America. With
22 people on the field constantly, and a minimumof 50 players per team that play at different times
during the game, there are more opportunities for players to get hurt. Hockey is the runner-up to
concussion quantities. Though second, it has a relatively high rate of concussions considering the
comparatively lowerparticipation rate than football [1].In sports, it is not uncommon forspectators
to see their favorite players experience a hard hit ‘in the name of the game.’ In response, spectators
wince or make sound effects while watching someone else’s pain. The ‘normal’ sighting of
concussive impacts has desensitized younger generations to the detrimental effects of concussions.
Concussions have mostly neurological symptoms, making them difficult to diagnose.
Concussions present a wide range of medical signs and symptoms, including the loss of
consciousness, behavioral changes, amnesia, and cognitive impairment to name a few. It should be
noted that these symptoms are almost entirely neurological, making many concussions
unrecognized by athletes or unobserved by coaches and trainers [3]. Therefore, a large portion of
concussions go unreported. If no one is able to identify a concussion, the helmet is the last form of
protection for players.
Linear and rotationalacceleration have different effects on brain injuries.
A concussion occurs froman initial impulsive force that creates direct or indirect contact with the
head,face,neck,or elsewhere[1].These injuriescan occurdirectlyor indirectly,such as with a blow
to the head (direct) orbeing hitunexpectedlyin thebody (indirect).Unexpected hitsand un-tensed
muscles allow for injuries to happen more readily. When an impact occurs or affects the head, the
brain moveswith the impact’s momentum,making contactwith the skull.A studyon head injuries,
using linear acceleration, rotational acceleration, and the combination of them, found that
rotational acceleration contributed to more than 80% of brain strain, a strain-induced brain injury
[3]. The angle at which the impact comes from causes the brain to twist inside the skull, with the
possibility of it twisting while against the skull. The result of the brain shearing inside/against the
skull is called brain strain. Figure 1 shows the effects of a concussion resulting from an impact in
football.

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Figure 1. The anatomy of a concussion as told by linear and rotational acceleration.
Concussions are the result of a combination of linear and rotational acceleration. Linear
accelerations are ‘head-on’ hits which cause the brain to hit the inside of the skull. Rotational
accelerations are hits that come at an angle, causing the brain to shear, or twist, inside the skull.
The additional acceleration from a rotational accelerative impact may cause the brain to also
strike the inside of the skull [4].
Rotational acceleration takes into account the angle of travel and impact.
Linear acceleration occurs from impacts that move in a straight path. When one takes a hammer
and has their wrist locked so it cannot move, the hammer comes down straight, resulting in linear
acceleration. Rotational acceleration would occur if the wrist holding the hammer was unlocked
and allowed to move as forcewasapplied. Theresulting acceleration would includealinearportion,
one that went in the general direction, and a rotational portion. The rotational portion describes
that angle at which the nail was hit, the angle at which the hammer was at the impact, and the
angle that the nail went after impact.
Similarly for football, a linear hit is one that comes straight on with no angular difference between
the impactor and the impacted. A hit like this translates the brain inside the skull in one direction
until it makes contact with the skull and bounces off. Rotational acceleration in football is much
more common. Any impact that takes place where the impactor and impacted have any trajectory
difference will have a rotational component. A difference in trajectory is typically when the
impactor is running towardsaplayer, butthat player is occupied running in anotherdirection.This
is common for wide receivers in football. Wide receivers who are watching the quarter back and
running a predetermined route are hit by defensive players in the field who are watching both the
quarterback and them. These defensive players cover a lot of area and strike if necessary, and often
unexpectedly, for the wide receiver.
Acceleration Differentiation

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Therelationship betweenlinear and rotationalacceleration is often misunderstood.In earlytesting,
researchers suggested that linear acceleration was correlated to rotational acceleration. Therefore,
as long as linear acceleration was reduced, testing forrotational acceleration was not necessary [3].
The improvementof technologyhasallowed more datato be collected.Data obtained using helmet
impact sensors have identified rotational acceleration as a function of both linear acceleration and
the directionof the forceacting on the head [3].Therefore,whileincreasing the impact velocity will
increase both the linear and rotational accelerations, there is a factor of angle that will affect
rotational acceleration beyond that of linear acceleration. Additionally, past and present testing on
primates has shown it very difficult to induce a concussion without the use of rotational
acceleration, suggesting that rotational acceleration is necessary forconcussions to occur [3,5]. It is
these reasons that necessitate the need for rotational acceleration testing in helmets.
The types of mechanisms that will be discussed for linear and rotational acceleration testing will
have different mechanisms and accessories. For easier identification, certain categories of
comparison are listed below randomly.
Accessory Head Form Neck Type
Acceleration
Equivalence
Includes
Rotational Acc.
Option 1 NOCSAE Rigid Meets Average No
Option 2 Hybrid III Non-Rigid / Recoil Meets Maximum Yes
Table 1. Mechanism accessories that will be compared for realism.
2.0 Linear Acceleration Testing
NOCSAE is an important testing protocol. Through the years, NOCSAE has evolved with the
improvement of technology. Better testing methods come from improved scientific research on the
subject of impacts. The most recent advances in linear testing technology are the Head Impact
Telemetry System (HIT) and the Hybrid III method. Additionally, these newer methods have been
tested oncollege level and professional football.Improving safety at theseupper levels will improve
the youth level by the trickle-down-effect.
2.1 Initial Helmet Testing
Historically, NOCSAE tested rotational and linear acceleration separately.
In 1969, NOCSAE was formed to maintain minimum performance levels in protective sporting gear
[6]. By creating a single group to manage testing quantity and quality, the process of ensuring
equipment safety of 50 helmet models became much simpler. According to the original relations
found between head motion and head injuries, all mathematical modeling studies considered the
rotational motion separately from the linear component [6]. The final suggested performance
criteria for protective head gear was the following: reduce total head acceleration by placing a
deformable material between the head and the impact surface [6]. Such a material would reduce
the impact on the skull, reducing head injuries caused from impacts.

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The last decade of NOCSAE changes have increased protection the realism of impacts to
real-life play.
In the last decade, many important changes have occurred to the NOCSAE standard. Specifically,
the head form changed from a metal form to a plastic one [7]. Additionally, the severity index for
impact measurement was reduced from a maximum of 1500 (g) pulses per second to 1200 (g) force
pulses per second [7]. The ‘g’ used in the severity index measurement is the gravitational acting on
a stationary object which exists on the earth’s surface. 1 g is equal to 9.81 meters/s2
or 9.81
Newton/kilogram, the value of gravity.
An example of the severity index is in figure 2. Figure 2 shows how acceleration over time accounts
for safety or yields injury [3,8]. The limit of effective acceleration seen in figure 2(b) is not true to
research.Qualitatively,the figureistrue;thelongertime spent at higheraccelerationsisdangerous,
and likely to yield injury. The maximum value of the y-axis was originally set at a value ~3x that.
Though thislimitwas dropped from1500to1200,the overallaffectis that much higheraccelerations
met within the first second are not necessarily life-threatening.Overall, 2(a) show that a velocity of
~11+ m/s yields a Severity Index of the max, 1200 g’s. 2(b) reveals that this impact velocity cannot
occur over many milliseconds before it becomes life-threatening.
(a) (b)
Figure 2. (a) Gadd Severity index for accelerations to the head. (b) Conversion chart for
severity index. The current NOCSAE standard is set to 1200 g’s of acceleration per second. From
(a), 1200 g’s is 10.5 m/s velocity. From (b), it is understood that the 1200 g’s per second/10.5 m/s
velocity will occur for milliseconds after the impact occurs and begin to dissipate [3, 8].
NOCSAE has chosen linear acceleration as the main mode of testing.

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Before a committee had been put in charge of equipment testing, it was not unusual to find many
testing methods for one type of protective head gear [6]. This was the result of the simulation and
the testing method between headgear and head injury not being established in the 1970s. In
addition, linear acceleration was singled out as the most important variable for measurement [6].
This is because linear acceleration effects a larger surface area on the skull as it impacts straight on
rather than at an angle. Affecting a larger area creates a larger impact in accelerative force. The
rotational component is limited mathematically by the angle at which is occurs. Only a part of the
total acceleration will impact the helmet. The remaining acceleration will do damage by moving
the head unnaturally. In 1969 when the original specimen testing occurred, all of the specimen
tested with rotational accelerationsuffered aconcussion.Noneof thelinearly tested specimen were
concussed [3, 6]. This suggests that it is not always the amount of force that is fatal, but the type or
combination of them.
The lineardroptest is themain test used in theNOCSAE standard and onlytests linearacceleration
[9]. To test, a helmet is attached to the NOCSAE head form and dropped in a controlled setting.
The helmet is tested in 6 locations, as seen in figure 3. A stationary anvil is at the bottom of the fall
to create the impact. The drop height is approximately 1.52 meters for every position tested and
acceleration of each drop occurs by gravity [9]. Once the impact occurs, the drop portion of the
mechanism is locked, keeping the helmet from being able to bounce back [9]. Additionally, the
tests do not include the face mask attached to the helmet shell, which seems counterintuitive to
how impacts actually occur during game play. Removing the helmet, though, allows for better
testing of specific locations, such as the front or front boss.
(a) (b)

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Figure 3. (a) A representation of the positions tested on football helmets during NOCSAE’s
linear drop test. (b) Impact locations based on helmet quadrants. Linear drop testing uses
the moving helmet to strike a stationary anvil on 6 specific locations: front, side, rear, top, and
front and rear diagonals or ‘bosses’ [9].
Beyond the linear drop test, NOCSAE does not attach a rating system on how well helmets perform
during the test [9]. It is anticipated that helmets from different manufacturers would perform
differently during the test; yet the only information given by testing is that each helmet passed the
test. This open ended method leaves a large range for helmets to ‘score’ during the testing process.
Meanwhile, the only information to consumers is the pass/fail aspect of the test. There is not a
national rating system to understand one helmet’s capability to tolerate an impact better than
others.
2.2Newly Proposed Linear Testing Methods
The NOCSAE standard and Hybrid III are being compared to the Head Impact Telemetry System
(HIT). The comparison is to prove their methods for linear acceleration testing are accurate to on-
field impacts.
The Head Impact Telemetry System (HIT) measuresimpacts that occur in play.
The Head Impact Telemetry (HIT) systemis a wireless sensorpad-system which is implantable into
helmets between the padding and the shell [9,10]. By being placed before the padding,
measurements of the raw accelerative impacts during play and practice are able to be captured by
the strategically placed sensors. The sensors relay information quickly back to a computer. In
addition, wireless capabilities allow the sensors to be re-placed depending on the player’s football
position.
The location of the sensors is important for the HIT system, which can be seen in figure 4.
Specifically,the sensorsareplaced inlocations whereimpacts havebeen recorded tohaveoccurred;
this is identifiable through video recordings of game-play [9,10]. The location of the sensors allows
measurements of the forces that occurs in that area during an impact. When an impact occurs, the
shell of a helmet will disperse the force as evenly as possible over the entire shell, reducing the
concentration of the impact in one location [9]. If placed at the direct location of the impact, a
sensor will get the concentrated acceleration data for the impact. Sensors nearby will collect data
for the dispersive acceleration spread across the helmet shell.

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Figure 4. An x-ray of the HIT system implanted into a helmet and look at the sensor pad
put into helmets. The wireless sensor system goes between the helmet padding and outer shell
to collect raw acceleration data prior to reaching the padding, which acts as a further dispersant
of the accelerative force [11,12].
HIT hasbeen used inboth collegeand professionalfootball applications during practiceand games.
For college football, HIT was originally implemented at Dartmouth University, which is located
near the lab at which it was designed and constructed. When used in the National Football League
(NFL), a maximum acceleration speed of 11.7m/s was recorded for tackles in the open field [9]. This
acceleration value was noted for comparison for the NOCSAE and Hybrid III methods discussed
later in this paper.
The Hybrid III method tests linear acceleration through thelinear impact test.
The Hybrid III method uses a different test for linear acceleration testing. The linear impactor test
places a helmet with facemask attached onto a different head form and non-rigid neck. The
mechanism, best understood from figure 5 (a), impacts the stationary helmet/head form/neck in a
specific location based on helmet positioning. Some of the positions can be seen just before impact
in figure 5 (b) [9,13]. The acceleration of the impact is changed by creating a larger pressure in the
piston, which activates the impactor to hit the helmet with a specific force. The linear bearing table
allows for the head form/helmet/neck to naturally recoil in response to the impact and move
backwards with inertia.

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(a) (b)
Figure 5. (a) Linear Impactor test apparatus of the Hybrid III method. (b) Four primary
impact sites tested in the linear impact test. The test uses an impactor which strikes the
stationary head form/helmet combination. After initial contact, the impactor and head form are
able to travel backwards in the direction of the impact [9,13].
Similarly to the linear drop test, sensors in the helmet test to ensure a severity index of 1200 (g’s per
second) is not surpassed. Ultimately, this test also does not rate helmets on their ability to absorb
and distribute acceleration protectively, thus remaining as pass/fail in the eyes of consumers [10,11].
Additionally, the difference in fit is an issue discussed later in this paper, as the head does not
include the bottom rear where part of the occipital lobe sits. This portion of this head form is
missing to attach the non-rigid neck, seen in figure 6.
Hybrid III NOCSAE
Figure 6. A photo of the two different head forms used in NOCSAE and Hybrid III helmet
testing. The NOCSAE head is a better representation of helmet fit while the Hybrid III head has
the impact-reaction found in head impacts in football. A chunk of the head for the Hybrid III
head form was removed to allow proper attachment of the recoil neck [13]

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2.3The Accuracyof Linear Acceleration Testing
Using HIT as the ‘control’ measurement for actual in-play data, NOCSAE and Hybrid III’s linear
acceleration tests will be compared for actual acceleration and locational compatibility.
Linear Acceleration Testing vs Average Actual Play Hits is strongly correlated.
The linear regression of the hit velocities and locations for both the NOCSAE drop test and Hybrid
III linear impact test were of similar acceleration and location, as shown in figure 7. The
investigation into how accurately these methods measure linear acceleration has shown that both
have their strengths and weaknesses.
(a) (b)
Figure 7. (a) NOCSAE comparison of HIT data for linear acceleration accuracy. (b) Hybrid
III linear regression for linear acceleration accuracy. Both charts show a strong relationship
between the testing done for linear acceleration and the on-field hits compared to them. The
comparison peak of NOCSAE and HIT would have a similar correlation to that of Hybrid III and
HIT. The proof that NOSCAE linear acceleration testing is occasionally greater than what is
recorded on-field is reassuring. The regression analysis for Hybrid III is r2
= 0.903 [13,14].
3.0 STAR Methods Comparison
The football STAR and hockey STAR method differ considerably for the similarity between
concussions found in the sports.
3.1 Comparison of head injuries in sports

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Onecontroversyof sports ishowsport popularity affectsmediaviewsof importantissues. Whatever
is most popular will be shown on the front page rather than what could be deemed most important
world-wide.
Football concussions are seen as more prominent over hockey because of popularity.
Head injuriesforsportstend to be recognized bypopularityof the sport.With moremoneyinvested
by the NFL than the National Hockey League (NHL), more athletes active at once on television
screens, and more availability for playing football long term, greater popularity is given to football
than hockey [15]. While most speculation of the popularity span is attributed to the higher cost of
playing hockey long term, hockey statistically has more head-related injuries and concussions than
the game of football, which suffers from a larger range of injuries [1].
Risk analysis modeling, STAR, is hockey’s rotationalacceleration formof testing
helmets.
The newest method of protective testing, the Summation of tests for Analysis of Risk (STAR), uses
a multiple-variable injury risk function to rate helmets with a meaningful metric for consumer
understanding [16]. Testing methods for the STAR formula uses two fundamental principles:
1. Tests performed are weighted on the frequency of that impact occurring.
2. Decreasing acceleration of the impact will decrease head injuries, therefore decreasing
the risk of concussions.
The hockey STAR formula uses a test matrix of 3 impact levels and 4 impact locations, equaling 12
tests per helmet. By performing the tests twice on a pair of helmets (4x total), 48 total data points
are collected per helmet model [16]. The second helmet’s set of tests are a check for repeatability
and variability in the testing. The testing mechanism can be seen below in figure 8, and contains
many of the suggested changes that would be used for linear acceleration, such as the NOCSAE
head form with a non-rigid neck for on-field accuracy. Once the data is collected, it is plugged into
the risk function to determine the probability of a concussion occurring as a result of those hits [5].

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(a) (b)
Figure 8. (a) The STAR method impact mechanism. (b) A close up of the 4 positions tested
by football and hockey star. The mechanism uses a pendulum, NOCSAE head form, and non-
rigid Hybrid III neck to perform impact testing. These images are taken from a Hockey STAR
report, which does not include face masks where football STAR would. Testing locations were cut
down from 6 to 4 because of the availability of changing the angle of impact easily with use of a
pendulum as the impactor [16].
As seen previously, the HIT system is used for testing in the helmets. In STAR, HIT sensors are
located in the padding rather than the area between the padding and the shell [16]. By placing the
sensors closer to the skull, data is specifically collected for how the acceleration reaches and acts
on the skull. This method focuses on how the skull is affected, which is the last defense before
injury occurs.
The STAR method rates helmets using concussion probabilities [16]. Concussion probabilities are
listed differently than star safety ratings, where typically higher star ratings score greater in safety.
In the STAR function, the lower the number, the lower probability of a concussion; most
importantly, these numbers are available to the general public who are purchasing these helmets.
Hockey STAR, unlike football STAR, includes rotational acceleration in testing.
Hockey STAR differs from football STAR by including the rotational element of acceleration as its
own variable in the risk analysis equation [16]. Figure 9 shows the football and hockey STAR
equations side-by-side. The football STAR equation also shows that there are five separate drop
height tests per location on the helmet tested. The only difference between this method and the
NOCSAE linear drop test is the number of heights used for the locations tested. Football STAR
uses20 tests per helmet,which, if done4total times, is 80data setsper model.Additionally,football

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STAR would include the face masks during testing as they are a better representation of impacts
during play.
(a) (b)
Figure 9. (a) Football STAR equation. (b) Hockey STAR equation. The football STAR
equation features L, the head impact location, H, drop height, and R(a), linear acceleration.
Hockey STAR features L, the head impact location, θ, the angle of the impact, and R(a,α), linear
and angular (rotational) acceleration of the impact [16].
Changing thefootballSTARmethod tousing apendulumand rotationalacceleration would provide
a better testing method overall. Additionally, there are two key differences found in the hockey
STAR function which build in ethical and protective factors that the game of football could benefit
from [16]:
1. Youth, college, and professional hockey data for men and women were included in the
study to best represent all possible impacts that occur in the sport.
2. Hockey STAR anticipates that only 10% of concussions will be diagnosed by doctors.
If football were to implement these factors into their testing and rating system, youth football
players, in addition to professional and college players, would benefit from the safety factors built
into the design. Safety as an overall issue, changing and implementing rotational acceleration
would impacta largeportion of youths,seen in figure9,thusimpacting thefutureof theU.S.,where
football is the most popular.

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Figure 9. A population pyramid of football players in the United States by level and age.
The majority of football players are developing youth. The impact of increasing safety with
rotational acceleration testing and development in design is critical for their brain development
and healthy aging [18].
4.0 Recommendations
The optimal helmet testing standard takes into consideration the best set of testing methods. This
means that the head used is ideal, and most similar to that of a human head. Additionally the neck
and/or testing method will allow for the natural response of impact, which is recoil. Proper testing
methods will use impact accelerations that are equivalent to those found in play. Finally, the best
testing method will allow fordifferentangularhitdirectionsduringtesting,which isseen in football
games. The breakdown of points will be as follows:
 Head use for helmet fit (15 points)
 Neck used for impact recoil (15 points)
 Accelerations equivalent to impacts occurring in play (40 points)
 Testing allowed for angular hits and directions (30points)
Both head and neck use have the same amount of points because they both affect how accurate
tests are incomparisonto in-play hits.Accelerationsequivalent to impactsoccurring in playis given
the greatest amount of points because without proper accelerations, the tests lack meaning.
Allowing for angular hits during testing is second highest because with appropriate acceleration
levels, these hits are most like those that occur in play and will provide crucial information about
the protection of football helmets.
The best head for used was found to be the NOCSAE head based on fit for testing.
For Hybrid III, one large issue was the fit of the helmet on the head. Hybrid III heads were unable
to withstand some of the hits, as the improper fit caused the helmet to rotate on the head form and
roll off the head [12]. This made collisions to the frontal and rear bosses challenging for testing and
the data unreliable. The Hybrid III method head form is the same head as the automobile crash test
dummy, formed to be the ‘average male’ head. Specifically, it is comprised of a steel inner skull and
a vinyl deformable skin [10]. The NOCSAE head was shaped from cadaver head scans and blow
molded outof polyethylene. Insidethe‘skull’ is glycerin,a thick polymer, to representthe brain[9].
The STAR method also utilizes the NOCSAE head for testing because of the ideal fit.
The best neck used is one that is non-rigid or a test apparatus thatallows for recoil upon
impact.
The neckattached to the NOCSAE head formis a rigid component.HITfound noissuesin thehead
form itself. Comparison to HIT did determine that the rigid neck and locking system was not
accurate in response of impacts found in play, where neck and heads tend to snap away/back from
where they are hit. The neck attached to the Hybrid III head form is not rigid and able to move in

18
response to the impact [9]. The mechanism used for hockey STAR uses a non-rigid neck similar to
Hybrid III that allows recoil from the base.
HIT determined that hockey STAR testing was reaching impactvelocities found in play.
For the lineardroptest to reach maximumaccelerationsfound in play,HITdetermined thata much
higher height must be used. With an arbitrary current height of 1.52 meters, the velocity at impact
is only5.4 m/s,abouthalf of whatwas found asthemaximumin theNFL (11.7m/s).Itwas calculated
that a drop height of over 6 meters (20 feet) would be required to reach 11.0 m/s at impact [10].
While this is attainable, it is hardly practical. This is because the mechanism instantaneously locks
the drop mechanism after the impact, becoming motionless [9]. The anvil, as stationary, cannot
absorb energy of the impact and the rigid neck and lock keeps it from bouncing up in response to
the impact. Inpractice, dropping ahelmet/head form~20 feetin the air ontoan anvil would require
mechanism changes to occur.
For the linear impactor test to reach maximum accelerations found in play, HIT determined that
an even higher impact velocity than 11.0 m/s was necessary [13]. Unlike NOCSAE’s drop test which
becomes motionless after impact, the helmet/head form and impactor are able to move with the
force of the impact after initial contact. Understandably, the impact moves the helmet back, in the
direction of the force, and the impactor back where it came from. The movement of the impactor
in responseof thehit is an absorption of kinetic energy,which takes away fromthetotal forcegoing
towards the helmet. The reduction from the impactor causes a necessary increase in the original
force to compensate for the loss.
When compared to HIT, the hockey STAR method used a large range of impact velocities, reaching
the maximum that is anticipated with on-field play. The groupings of test velocities and multiple
orientations maximizes the testing possibilities, increasing the range of test locations, and allowing
testing for bizarre impacts that occur in football.
Hockey STAR is the most realistic method to allow angular impactsduring testing.
The NOCSAE standard, Hybrid III method, and football STAR only test linear acceleration. The
many positioning options allowed with the base and pendulum of the hockey STAR method gives
an assortment of testing locations. These impacts, even the rare ones, need to be tested to ensure
that helmets are capable of mitigating the force to the skull.
5.0 Conclusion
Through the design matrix, the points tally up and are seen in figure 10.

19
Figure 10. A bar chart by criterion and points of the design matrix. This figure visually
shows how the methods compare rather than just numerically.
Football STAR is comparable to Hybrid III because of the lack of angular hit directions and the
similar drop heights used in NOCSAE. As proven earlier using HIT, this data is not representative
of in-play impacts found in the game of football. The hockey STAR method allowed for a greater
variability of testing areas and impacts, with a range of impact accelerations that are found during
play. The pendulum mechanism allows for both linear and rotational acceleration testing. The
added bonusesbuiltinto the hockeySTAR methodsarealso worthwhile:youth datashould bebuilt
into the standard and anticipation that less than 10% of concussionswill be identified. This method
takes into consideration facts that builds extra security into the design, protecting youth from the
dangers of head injuries.
Until the testing changes, it is important to continue to spread information about head injuries.
Increasing knowledge and talking about the issue is the only way to keep the topic at the forefront
of sports. While future testing should be done on the hockey STAR method for use in football
helmet testing, the design criterion suggests that this method will optimize helmet protection for
the players and instigate new protective designs for the future.
15 15 1515
1520 25 25
35
25
0
20
40
60
80
100
NOCSAE Hybrid III Football STAR Hockey STAR
PointsScored
Standard
Helmet Standard Comparison
Head Form
Type
Neck Type
Acceleration
Equivalence
Angular Hit
Directions

20
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[12] http://www.riddell.com/riddell/wp-content/uploads/2013/06/insite_main_img.png

21
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