The Effect of Soft-Shell Helmet Add-Ons on Concussion Risk in FootballNicholas Stiansen1, Steve Rowson2

1University of Pennsylvania School of Engineering and Applied Science2Virginia Tech Department of Biomedical Engineering and Mechanics

• Concussion is one of the most prominent

traumatic injuries in sports, affecting up to

3.8 million athletes annually.1 Concussion is

induced from both linear and rotational

acceleration of the head, with linear

acceleration altering pressure gradients in

the skull and rotational acceleration

generating shear strain in the brain.2,3

• Studies show concussion occurs at an

average linear acceleration of about 105 g,

Methods

Conclusions

Introduction

Presented at the 2016 Summer Undergraduate Research Symposium

ResultsA Xenith Epic, a Schutt AiR XP Pro, and a Riddell 360, equipped with

and without the Guardian Cap were impacted in four impact locations:

The helmets were fitted onto a 50th percentile NOCSAE head attached

to a Hybrid III neck. All testing was performed on the pneumatic linear

impactor test system (below).

Data were collected for each of the 432 impacts through three

accelerometers and three angular rate sensors located in the headform.

Linear Data underwent a CFC 1000 filter and rotational data underwent

a CFC 155 filter, then all data had offset removal before analysis. Peak

linear acceleration, peak rotational acceleration, and peak

rotational velocity were determined for each trial.

Additionally, peak linear acceleration and peak rotational

acceleration were used to calculate concussion risk for each impact

with the following formula, derived from Rowson et al.9

• The Guardian Cap performed best on direct high-velocity impacts

(front and side) and had little effect on glancing impacts.

• The rank of helmets benefitting most from the Guardian Cap (Schutt,

Xenith, Riddell) is the same as the order of helmets with the worst

STAR rating to the best STAR rating. This confirms the idea that poor

helmets will see a greater benefit from wearing the Guardian

Cap, while better helmets will see minimal improvement.

• The highest reduction in concussion risk was 24%. Most test

conditions saw no change in concussion risk from the Guardian Cap.

• The effect of the Guardian Cap varied by helmet, impact location, and

velocity. On average, it reduced concussion risk by 2.2%. While it

may do no harm, the benefit the Guardian Cap provides is small.

C BIVirginia Tech – Wake Forest University

Center for Injury Biomechanics

Front Front Glance Side Side Glance

And at three impact velocities, representative of potentially concussive

impacts in football: 7.0 m/s, 8.5 m/s, and 9.5 m/s.

although there is no known acceleration threshold for concussion.4,5

• It has been shown that helmet design can significantly reduce head

acceleration and, inherently, concussion risk.6,7

• Additionally, companies are now creating external helmet

enhancements that supposedly further reduce concussion risk. The

most popular of these add-ons is the Guardian Cap, a soft-shelled

polyurethane cap that claims to reduce impact by 33%.8

• However, the effect of the Guardian Cap has not been quantified and

there is even some concern that a soft-shelled cap could increase

injury risk due to greater friction between helmets during impact.

• The objective of this study was to evaluate the Guardian Cap in

its ability to reduce concussion risk.

An impacting face simulating a helmet

emulated helmet-to-helmet impacts. To

represent the striking player also

wearing the Guardian Cap, part of an

extra cap was attached to the

impacting face with adhesive.

Citations

The presence of the Guardian Cap had a significant effect on

concussion risk for the Xenith Epic at 7 m/s and 8.5 m/s ( p < 0.013), for

the Schutt AiR XP Pro at all impact velocities (p < 0.007), and for the

Riddell 360 at 7 m/s and 9.5 m/s (p < 0.010).

[1] Langlois JA, Rutland-Brown W, Wald MM. The epidemiology and impact of traumatic brain injury: A brief overview. The Journal of head trauma rehabilitation. 2006;21(5):375-8. [2] Gennarelli

T, Ommaya A, Thibault L. Comparison of translational and rotational head motions in experimental cerebral concussion. Proc. 15th Stapp Car Crash Conference. 1971;797-803. [3] Hardy WN,

Mason MJ, Foster CD, et al. A study of the response of the human cadaver head to impact. Stapp car crash journal. 2007;51(17-80. [4] Pellman EJ, Viano DC, Tucker AMCasson IR, Waeckerle

JF. Concussion in professional football: Reconstruction of game impacts and injuries. Neurosurgery. 2003;53(4):799-812; discussion -4. [5] Rowson S, Duma SM. Development of the star

evaluation system for football helmets: Integrating player head impact exposure and risk of concussion. Ann Biomed Eng. 2011;39(8):2130-40. [6] Rowson S, Duma SM, Greenwald RM, et al.

Can helmet design reduce the risk of concussion in football? Technical note. Journal of Neurosurgery. 2014;120(4):919-22. [7] Viano DC, Halstead D. Change in size and impact performance of

football helmets from the 1970s to 2010. Ann Biomed Eng. 2012;40(1):175-84. [8] The guardian cap. http://www.guardiancaps.com/theguardiancap/. [9] Rowson S, Duma SM. Brain injury

prediction: Assessing the combined probability of concussion using linear and rotational head acceleration. Ann Biomed Eng. 2013;41(5):873-82.

𝑅(𝑎, 𝛼) =1

1 + 𝑒−(−10.2+0.433∗𝑎+0.000873∗𝛼−0.000000920∗𝑎𝛼)

a = Peak Linear Acceleration; 𝛼 = Peak Rotational Acceleration

Impact

Location

Impact

Velocity

(m/s)

Average Linear

Acceleration

Difference (g)

Average Rotational

Acceleration

Difference (rad/s2)

Average

Concussion Risk

Difference (%)

7 5.0 79 0.2%

Front 8.5 5.2 46 1.1%

9.5 0.2 8 3.0%

7 -1.3 -421 0.0%

Front

Glance8.5 -2.8 -52 0.0%

9.5 -4.3 -177 0.0%

7 5.7 -117 0.8%

Side 8.5 7.3 439 10.9%

9.5 0.3 1013 16.1%

7 0.9 -344 -0.1%

Side

Glance 8.5 -1.0 -663 -1.0%

9.5 -3.1 -1069 -4.4%

OVERALL: 1.0 -105 2.2%

Differences in Concussion Risk By Helmet Guardian Cap

Improves

Performance

Concussion

Risk Difference

Guardian Cap

Worsens

Performance Front Front

GlanceSide Side

Glance

Front Front

GlanceSide Side

Glance

Guardian Cap

Improves

Performance

Concussion

Risk Difference

Guardian Cap

Worsens

Performance

Concussion

Risk Difference

Guardian Cap

Worsens

Performance

Guardian Cap

Improves

Performance

Front Front

GlanceSide Side

Glance

Xenith Epic

Schutt AiR XP Pro

Riddell 360