Editorial: Leather football helmets

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At the request of the editor we are providing this editorial to Rowson et al.'s “Biomechanical performance of leather and modern football helmets. Technical note.”5 In their paper, Rowson et al. have attempted to provide additional data and insight to clarify certain conclusions reported in an earlier American football helmet study by Bartsch et al.1

In the real world, American football collisions always involve combinations of linear and rotational motion that may pose risk to the participant's short-term and long-term brain health. When Rowson et al.'s rigid drop tests are contrasted with Bartsch et al.'s common “on-field” laboratory impacts, it is of utmost importance to consider the testing methodologies and head motions induced.

Rowson et al. drop-tested helmets against a rigid surface with infinite mass and stiffness under standard conditions.4 These standard drop tests allowed mainly linear head motion and benchmarked skull fracture risk. Their data showed that modern helmets, which are designed to perform under these standardized testing conditions, performed significantly better than leather helmets. A real-world analogy to these results is that one's skull would be significantly better protected when running headfirst into a brick wall while wearing a modern American football helmet versus a vintage leather helmet.

In contrast, Bartsch et al. tested a helmeted head form striking a second helmeted head form that was mounted on a flexible neck, permitting linear and rotational head motion. These laboratory tests represented an approximation of two players colliding headfirst while wearing modern and vintage helmets under common on-field conditions that could induce skull, brain, and neck loading. Bartsch et al.'s data demonstrated that in these common on-field impact scenarios, modern and vintage leather helmets frequently protected the skull and brain comparably. The two studies used disparate methodologies, examined different injury risk metrics, and hence produced divergent results. Therefore, Rowson et al.'s additional data do not clarify the limitations of, but rather stand in contrast to, the data presented in Bartsch et al.'s study.

Rowson et al. are correct in recharacterizing the conclusions of Bartsch et al.'s experiments by stating “leather helmets performed similarly to modern helmets when struck by a Riddell VSR4 helmet….” However, even with this recharacterization, the resulting differences between the studies reported by Rowson et al. and by Bartsch et al. provide ample motivation to reassess the rigid drop test standard. These differences also suggest the need to continue physics-based helmet performance investigations under on-field conditions that induce linear and rotational head motion. Furthermore, Rowson et al. as well as others have recently published on-field impact data2,3,6 validating the fact that Bartsch et al.'s “on-field” laboratory impact conditions generated linear and rotational head motions similar to those commonly occurring in the real world. It is emphasized that these common linear and rotational real-world head motions have now been conclusively proven to be markedly different from Rowson et al.'s drop test head motions.

We now have two studies—by Rowson et al. and by Bartsch et al.—that provide dissimilar results in spite of apparent similarities in head forms, helmets, impact energy, and impact momenta. The difference in results can be conclusively explained by the two very different testing methodologies used and the head motions induced. We also can conclude that not all impact tests are created equal. Therefore, we must continue examining experimental protocols to achieve better quantification of helmet performance under conditions in which on-field physics testing methodologies and relevant injury risk metrics are considered.

Disclosure

The authors report no conflict of interest.

References

  • 1

    Bartsch ABenzel EMiele VPrakash V: Impact test comparisons of 20th and 21st century American football helmets. Laboratory investigation. J Neurosurg 116:2222332012

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  • 2

    Beckwith JGGreenwald RMChu JJCrisco JJRowson SDuma SM: Head impact exposures sustained by football players on days of diagnosed concussion. Med Sci Sports Exerc 45:7377462013

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    • Export Citation
  • 3

    Daniel RWRowson SDuma SM: Head impact exposure in youth football. Ann Biomed Eng 40:9769812012

  • 4

    NOCSAE: Standard Performance Specification for Newly Manufactured Football Helmets Overland, KSNational Operating Committee on Standards for Athletic Equipment(http://nocsae.org/wp-content/files_mf/1348109354ND00211m12MfrdFBHelmetsStandardPerformance.pdf) [Accessed April 2 2013]

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  • 5

    Rowson SDaniel RWDuma SM: Biomechanical performance of leather and modern football helmets. Technical note. J Neurosurg [epub ahead of print May 7 2013. DOI: 10.3171/2013.3.JNS121735]

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  • 6

    Rowson SDuma SMBeckwith JGChu JJGreenwald RMCrisco JJ: Rotational head kinematics in football impacts: an injury risk function for concussion. Ann Biomed Eng 40:1132012

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Response

We thank Bartsch et al. for their commentary on our technical note. Our purpose was to offer additional data by using a different testing methodology that could offer insight as to how leather football helmets could perform similarly to modern football helmets. Our contrasting results offer an explanation through our differing impact conditions. Specifically, we wanted to draw attention to the effect that a compliant impactor can have on comparisons of relative helmet performance. While our biomechanical assessment can be found in our technical note, we aim to highlight several points with this response.

First, we agree with Bartsch et al. that laboratory testing should be representative of impacts that players experience on the field. We have developed laboratory testing methods that evaluate relative helmet performance based on our 10 years of on-field head impact data.4,6 From these data, we understand the head impact exposure (defined as the cumulative frequency, location, and acceleration magnitude of impacts) of the collegiate football player.2,3 We generalize and emulate head impact exposure with 20 laboratory testing conditions in our Summation of Tests for the Analysis of Risk (STAR) evaluation system.14

Second, not all helmets are created equal in their ability to reduce concussion risk. Head acceleration magnitude is correlated to concussion, and is a good predictor of injury with high sensitivity.5,7–10,15 Helmets that modulate the impact energy transfer so that peak head acceleration is lower reduce concussion risk. Concussion risk reduction estimated by the STAR evaluation system is supported by clinical on-field data quantifying concussion incidence rates by helmet type.1,15

Third, we agree with Bartsch et al. that the laboratory testing conditions used to assess relative helmet performance should evaluate linear and rotational head acceleration. For this reason we have developed a new injury metric that quantifies concussion risk when considering both linear and rotational head acceleration.13 We are in the process of refining the STAR evaluation system to reflect this based on our on-field measurements of linear and rotational head acceleration.11,12,16

Experimental testing conditions should be considered when interpreting data. Overall, modern helmets are vastly superior to leather helmets; we and Bartsch et al. agree on that. As we continue to advance our understanding of head impacts in football as well as our understanding of human tolerance, additional progress can be made on improving helmet design criteria aimed at reducing concussion risk.

References

  • 1

    Collins MLovell MRIverson GLIde TMaroon J: Examining concussion rates and return to play in high school football players wearing newer helmet technology: a three-year prospective cohort study. Neurosurgery 58:2752862006

    • Search Google Scholar
    • Export Citation
  • 2

    Crisco JJWilcox BJBeckwith JGChu JJDuhaime ACRowson S: Head impact exposure in collegiate football players. J Biomech 44:267326782011

    • Search Google Scholar
    • Export Citation
  • 3

    Crisco JJWilcox BJMachan JTMcAllister TWDuhaime ACDuma SM: Magnitude of head impact exposures in individual collegiate football players. J Appl Biomech 28:1741832012

    • Search Google Scholar
    • Export Citation
  • 4

    Daniel RWRowson SDuma SM: Head impact exposure in youth football. Ann Biomed Eng 40:9769812012

  • 5

    Duhaime ACBeckwith JGMaerlender ACMcAllister TWCrisco JJDuma SM: Spectrum of acute clinical characteristics of diagnosed concussions in college athletes wearing instrumented helmets. Clinical article. J Neurosurg 117:109210992012

    • Search Google Scholar
    • Export Citation
  • 6

    Duma SMRowson S: Past, present, and future of head injury research. Exerc Sport Sci Rev 39:232011

  • 7

    Funk JRRowson SDaniel RWDuma SM: Validation of concussion risk curves for collegiate football players derived from HITS data. Ann Biomed Eng 40:79892012

    • Search Google Scholar
    • Export Citation
  • 8

    Greenwald RMGwin JTChu JJCrisco JJ: Head impact severity measures for evaluating mild traumatic brain injury risk exposure. Neurosurgery 62:7897982008

    • Search Google Scholar
    • Export Citation
  • 9

    King AIYang KHZhang LHardy WViano DC: Is head injury caused by linear or angular acceleration?. Presented at the International Research Conference on the Biomechanics of Impact (IRCOBI)Lisbon, Portugal2003. (http://snell-helmets.org/docs/articles/hic/King_IRCOBI_2003.pdf) [Accessed April 2 2013]

    • Search Google Scholar
    • Export Citation
  • 10

    Pellman EJViano DCTucker AMCasson IRWaeckerle JF: Concussion in professional football: reconstruction of game impacts and injuries. Neurosurgery 53:7998142003

    • Search Google Scholar
    • Export Citation
  • 11

    Rowson SBeckwith JGChu JJLeonard DSGreenwald RMDuma SM: A six degree of freedom head acceleration measurement device for use in football. J Appl Biomech 27:8142011

    • Search Google Scholar
    • Export Citation
  • 12

    Rowson SBrolinson GGoforth MDietter DDuma S: Linear and angular head acceleration measurements in collegiate football. J Biomech Eng 131:0610162009

    • Search Google Scholar
    • Export Citation
  • 13

    Rowson SDuma SM: Brain injury prediction: assessing the combined probability of concussion using linear and rotational head acceleration. Ann Biomed Eng [epub ahead of print]2013

    • Search Google Scholar
    • Export Citation
  • 14

    Rowson SDuma SM: Development of the STAR evaluation system for football helmets: integrating player head impact exposure and risk of concussion. Ann Biomed Eng 39:213021402011

    • Search Google Scholar
    • Export Citation
  • 15

    Rowson SDuma SM: The Virginia Tech response. Ann Biomed Eng 40:251225182012. (Letter)

  • 16

    Rowson SDuma SMBeckwith JGChu JJGreenwald RMCrisco JJ: Rotational head kinematics in football impacts: an injury risk function for concussion. Ann Biomed Eng 40:1132012

    • Search Google Scholar
    • Export Citation

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Article Information

Please include this information when citing this paper: published online May 7, 2013; DOI: 10.3171/2012.12.JNS122174.

© AANS, except where prohibited by US copyright law.

Headings

References

  • 1

    Bartsch ABenzel EMiele VPrakash V: Impact test comparisons of 20th and 21st century American football helmets. Laboratory investigation. J Neurosurg 116:2222332012

    • Search Google Scholar
    • Export Citation
  • 2

    Beckwith JGGreenwald RMChu JJCrisco JJRowson SDuma SM: Head impact exposures sustained by football players on days of diagnosed concussion. Med Sci Sports Exerc 45:7377462013

    • Search Google Scholar
    • Export Citation
  • 3

    Daniel RWRowson SDuma SM: Head impact exposure in youth football. Ann Biomed Eng 40:9769812012

  • 4

    NOCSAE: Standard Performance Specification for Newly Manufactured Football Helmets Overland, KSNational Operating Committee on Standards for Athletic Equipment(http://nocsae.org/wp-content/files_mf/1348109354ND00211m12MfrdFBHelmetsStandardPerformance.pdf) [Accessed April 2 2013]

    • Search Google Scholar
    • Export Citation
  • 5

    Rowson SDaniel RWDuma SM: Biomechanical performance of leather and modern football helmets. Technical note. J Neurosurg [epub ahead of print May 7 2013. DOI: 10.3171/2013.3.JNS121735]

    • Search Google Scholar
    • Export Citation
  • 6

    Rowson SDuma SMBeckwith JGChu JJGreenwald RMCrisco JJ: Rotational head kinematics in football impacts: an injury risk function for concussion. Ann Biomed Eng 40:1132012

    • Search Google Scholar
    • Export Citation
  • 1

    Collins MLovell MRIverson GLIde TMaroon J: Examining concussion rates and return to play in high school football players wearing newer helmet technology: a three-year prospective cohort study. Neurosurgery 58:2752862006

    • Search Google Scholar
    • Export Citation
  • 2

    Crisco JJWilcox BJBeckwith JGChu JJDuhaime ACRowson S: Head impact exposure in collegiate football players. J Biomech 44:267326782011

    • Search Google Scholar
    • Export Citation
  • 3

    Crisco JJWilcox BJMachan JTMcAllister TWDuhaime ACDuma SM: Magnitude of head impact exposures in individual collegiate football players. J Appl Biomech 28:1741832012

    • Search Google Scholar
    • Export Citation
  • 4

    Daniel RWRowson SDuma SM: Head impact exposure in youth football. Ann Biomed Eng 40:9769812012

  • 5

    Duhaime ACBeckwith JGMaerlender ACMcAllister TWCrisco JJDuma SM: Spectrum of acute clinical characteristics of diagnosed concussions in college athletes wearing instrumented helmets. Clinical article. J Neurosurg 117:109210992012

    • Search Google Scholar
    • Export Citation
  • 6

    Duma SMRowson S: Past, present, and future of head injury research. Exerc Sport Sci Rev 39:232011

  • 7

    Funk JRRowson SDaniel RWDuma SM: Validation of concussion risk curves for collegiate football players derived from HITS data. Ann Biomed Eng 40:79892012

    • Search Google Scholar
    • Export Citation
  • 8

    Greenwald RMGwin JTChu JJCrisco JJ: Head impact severity measures for evaluating mild traumatic brain injury risk exposure. Neurosurgery 62:7897982008

    • Search Google Scholar
    • Export Citation
  • 9

    King AIYang KHZhang LHardy WViano DC: Is head injury caused by linear or angular acceleration?. Presented at the International Research Conference on the Biomechanics of Impact (IRCOBI)Lisbon, Portugal2003. (http://snell-helmets.org/docs/articles/hic/King_IRCOBI_2003.pdf) [Accessed April 2 2013]

    • Search Google Scholar
    • Export Citation
  • 10

    Pellman EJViano DCTucker AMCasson IRWaeckerle JF: Concussion in professional football: reconstruction of game impacts and injuries. Neurosurgery 53:7998142003

    • Search Google Scholar
    • Export Citation
  • 11

    Rowson SBeckwith JGChu JJLeonard DSGreenwald RMDuma SM: A six degree of freedom head acceleration measurement device for use in football. J Appl Biomech 27:8142011

    • Search Google Scholar
    • Export Citation
  • 12

    Rowson SBrolinson GGoforth MDietter DDuma S: Linear and angular head acceleration measurements in collegiate football. J Biomech Eng 131:0610162009

    • Search Google Scholar
    • Export Citation
  • 13

    Rowson SDuma SM: Brain injury prediction: assessing the combined probability of concussion using linear and rotational head acceleration. Ann Biomed Eng [epub ahead of print]2013

    • Search Google Scholar
    • Export Citation
  • 14

    Rowson SDuma SM: Development of the STAR evaluation system for football helmets: integrating player head impact exposure and risk of concussion. Ann Biomed Eng 39:213021402011

    • Search Google Scholar
    • Export Citation
  • 15

    Rowson SDuma SM: The Virginia Tech response. Ann Biomed Eng 40:251225182012. (Letter)

  • 16

    Rowson SDuma SMBeckwith JGChu JJGreenwald RMCrisco JJ: Rotational head kinematics in football impacts: an injury risk function for concussion. Ann Biomed Eng 40:1132012

    • Search Google Scholar
    • Export Citation

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