Research Papers

An Investigation of the NOCSAE Linear Impactor Test Method Based on In Vivo Measures of Head Impact Acceleration in American Football

[+] Author and Article Information
Joseph T. Gwin1

 Simbex, Lebanon, NH 03766; Thayer School of Engineering at Dartmouth, Hanover, NH 03755; Division of Kinesiology, University of Michigan, Ann Arbor, MI 48109-2214jgwin@umich.edu

Jeffery J. Chu2

 Simbex, Lebanon, NH 03766

Solomon G. Diamond

 Thayer School of Engineering at Dartmouth, Hanover, NH 03755

P. David Halstead

Sports Biomechanics Impact Research Laboratory, University of Tennessee, Rockford, TN 37853

Joseph J. Crisco2

Department of Orthopaedics, Alpert Medical School, Brown University, Providence, RI 02912; Rhode Island Hospital, Providence, RI 02903

Richard M. Greenwald2

 Simbex, Lebanon, NH 03766; Thayer School of Engineering at Dartmouth, Hanover, NH 03755


Corresponding author.


Conflict of Interest: Authors R. G., J. C., and J. C. have a financial interest in HIT System technology used to record in-vivo head impacts for this study.

J Biomech Eng 132(1), 011006 (Dec 17, 2009) (9 pages) doi:10.1115/1.4000249 History: Received October 09, 2008; Revised August 18, 2009; Posted September 18, 2009; Published December 17, 2009; Online December 17, 2009

The performance characteristics of football helmets are currently evaluated by simulating head impacts in the laboratory using a linear drop test method. To encourage development of helmets designed to protect against concussion, the National Operating Committee for Standards in Athletic Equipment recently proposed a new headgear testing methodology with the goal of more closely simulating in vivo head impacts. This proposed test methodology involves an impactor striking a helmeted headform, which is attached to a nonrigid neck. The purpose of the present study was to compare headform accelerations recorded according to the current (n=30) and proposed (n=54) laboratory test methodologies to head accelerations recorded in the field during play. In-helmet systems of six single-axis accelerometers were worn by the Dartmouth College men’s football team during the 2005 and 2006 seasons (n=20,733 impacts; 40 players). The impulse response characteristics of a subset of laboratory test impacts (n=27) were compared with the impulse response characteristics of a matched sample of in vivo head accelerations (n=24). Second- and third-order underdamped, conventional, continuous-time process models were developed for each impact. These models were used to characterize the linear head/headform accelerations for each impact based on frequency domain parameters. Headform linear accelerations generated according to the proposed test method were less similar to in vivo head accelerations than headform accelerations generated by the current linear drop test method. The nonrigid neck currently utilized was not developed to simulate sport-related direct head impacts and appears to be a source of the discrepancy between frequency characteristics of in vivo and laboratory head/headform accelerations. In vivo impacts occurred 37% more frequently on helmet regions, which are tested in the proposed standard than on helmet regions tested currently. This increase was largely due to the addition of the facemask test location. For the proposed standard, impactor velocities as high as 10.5 m/s were needed to simulate the highest energy impacts recorded in vivo. The knowledge gained from this study may provide the basis for improving sports headgear test apparatuses with regard to mimicking in vivo linear head accelerations. Specifically, increasing the stiffness of the neck is recommended. In addition, this study may provide a basis for selecting appropriate test impact energies for the standard performance specification to accompany the proposed standard linear impactor test method.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Sketch of linear impactor test apparatus (15)

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Figure 2

The NOCSAE linear drop test setup for all required impact locations (28)

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Figure 3

Testable locations (shown in light gray) for the current and proposed NOCSAE standards

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Figure 4

Impact location bins based on azimuth (left) and elevation (right) (30)

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Figure 5

CG resultant and CG projection for an in vivo rear location football impact

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Figure 6

Schematics of second-order (top) and third-order (bottom) mass-spring-damper models. The head/neck unit (M) is connected to a rigid body by springs (K,K1,K2) and a damper (B).

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Figure 7

Heat maps showing the concentration of impacts on the head surface: panel (a) contains data in the 0–200 GSI bin, panel (b) contains data in the 201–400 GSI bin, panel (c) contains data in the 401–600 GSI bin, and panel (d) contains GSI greater than 600

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Figure 8

Best fit exponential regressions of LI velocity versus GSI for all five impact locations. r2 values and regression parameters are given in Table 2.

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Figure 9

LI velocity versus GSI for rear location LI impacts (shown as circles). The best fit exponential regression for this location was GSI=7.31e0.46 (r2=0.95, dashed line). Solid lines highlight the 95th, 99th, and 99.9th percentile of in vivo impacts to the rear azimuth region, excluding impacts to the Q4 elevation region (top of the head).

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Figure 10

Mean values for each model parameter (Tw,ξ,Tp,Tz) grouped by impact type. Errorbars are ±1 SD. P-values for each one-way analysis of variance are shown.




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