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arxiv: 2507.09098 · v5 · pith:JS3K6SIEnew · submitted 2025-07-12 · ⚛️ physics.med-ph · physics.data-an

Linear Acceleration Is a Primary Risk Factor for Concussion and a Target for Prevention

Jessica A. Towns , Nicholas J. Cecchi , James W. Hickey , William T. O'Brien , Spencer S.H. Roberts , N. Stewart Pritchard , Jillian E. Urban , Joel D. Stitzel
show 4 more authors
Gerald A. Grant Michael M. Zeineh Stuart J. McDonald David B. Camarillo
This is my paper

Pith reviewed 2026-05-22 00:05 UTC · model grok-4.3

classification ⚛️ physics.med-ph physics.data-an
keywords concussionlinear accelerationrotational accelerationhead impactfootball helmetinjury preventionmouthguardrisk function
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The pith

Linear acceleration predicts concussions more accurately than rotational acceleration and can be targeted for prevention.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The authors measured head movements during actual diagnosed concussions in athletes using instrumented mouthguards. They discovered that linear acceleration of the head was a stronger predictor of injury than rotational acceleration, although rotational velocity also contributed useful information. From these measurements, they built injury risk functions that estimate high chances of concussion even from ordinary impacts in American football. They then tested a new helmet pad filled with liquid that reduces linear acceleration and found it lowered the estimated risk by as much as 52 percent. This work suggests that efforts to prevent concussions should focus on minimizing linear acceleration in head impacts.

Core claim

Using instrumented mouthguards to record head kinematics during diagnosed concussions, linear acceleration predicted injury with greater precision than rotational acceleration, while rotational velocity provided additional predictive value. Injury risk functions indicated substantial predicted concussion risk during typical impacts to an American football helmet. A liquid-filled helmet pad designed to attenuate linear acceleration reduced predicted risk by up to 52%. These results indicate that effective concussion prevention requires targeting linear acceleration.

What carries the argument

Injury risk functions derived from linear and rotational head kinematics recorded by mouthguard sensors during real concussions.

If this is right

  • Concussion risk remains high during typical impacts experienced in American football.
  • Targeting linear acceleration in helmet design can substantially lower predicted concussion rates.
  • Rotational velocity should be included in models of concussion risk alongside acceleration measures.
  • Prevention strategies focused only on rotational acceleration may be incomplete.
  • Modifications like liquid-filled pads offer a practical way to reduce injury risk by attenuating linear motion.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Helmet standards and regulations in contact sports could be updated to emphasize linear acceleration limits based on these risk functions.
  • Similar sensor-based studies in other sports might reveal whether linear acceleration is equally dominant outside of football.
  • Long-term tracking of athletes using the new pads could test if the 52% risk reduction translates to fewer actual concussions.
  • The emphasis on linear acceleration may prompt re-examination of older biomechanical models that prioritized rotation.

Load-bearing premise

The mouthguard sensors accurately measure head kinematics at the time of injury and the recorded impacts are the direct cause of the diagnosed concussions.

What would settle it

A prospective study in which football players wear the liquid-filled pads and the actual concussion incidence is compared to predictions from the risk functions without the pads.

Figures

Figures reproduced from arXiv: 2507.09098 by David B. Camarillo, Gerald A. Grant, James W. Hickey, Jessica A. Towns, Jillian E. Urban, Joel D. Stitzel, Michael M. Zeineh, Nicholas J. Cecchi, N. Stewart Pritchard, Spencer S.H. Roberts, Stuart J. McDonald, William T. O'Brien.

Figure 1
Figure 1. Figure 1 [PITH_FULL_IMAGE:figures/full_fig_p033_1.png] view at source ↗
read the original abstract

Head impacts can cause concussion, but the precise biomechanical conditions that produce injury remain uncertain. Rotational acceleration has long been posited as the primary cause and has guided concussion prevention strategies. Using instrumented mouthguards to record head kinematics of diagnosed concussions, we directly tested this hypothesis and found that linear acceleration predicted injury with greater precision than rotational acceleration, while rotational velocity provided additional predictive value. Injury risk functions derived from these measurements indicated substantial predicted concussion risk during typical impacts to an American football helmet. Introducing a liquid-filled helmet pad designed to attenuate linear acceleration reduced predicted risk by up to 52%. These results indicate that effective concussion prevention requires targeting linear acceleration.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 2 minor

Summary. The manuscript uses instrumented mouthguards to record head kinematics during diagnosed concussions and reports that linear acceleration predicts injury with greater precision than rotational acceleration, while rotational velocity adds predictive value. Injury risk functions derived from these data indicate substantial predicted concussion risk for typical American football helmet impacts. A liquid-filled helmet pad designed to attenuate linear acceleration is modeled to reduce predicted risk by up to 52%, leading to the conclusion that prevention strategies should target linear acceleration.

Significance. If the central empirical claims hold after addressing validation and statistical gaps, the work would have substantial significance by challenging the long-standing emphasis on rotational acceleration as the primary concussion mechanism. The quantitative modeling of a 52% risk reduction via a specific pad intervention provides a concrete, testable target for helmet redesign and could directly inform prevention protocols in contact sports.

major comments (3)
  1. [Methods and Results] Methods and Results sections: The comparative claim that linear acceleration predicts injury with greater precision than rotational acceleration is presented without reported sample sizes for concussion cases or control impacts, without statistical details (e.g., AUC values, p-values, confidence intervals), and without error bars or cross-validation. These omissions are load-bearing for assessing whether the precision ordering is robust.
  2. [Results] Injury risk functions (Results): The risk curves and the associated 52% risk reduction for the liquid-filled pad are derived post-hoc from the same set of measured concussion cases used to establish predictive performance. This creates circularity, as the 'predicted' risks for typical impacts represent fitted extrapolations rather than independent tests, directly affecting the strength of the prevention claim.
  3. [Methods] Methods: No independent validation, calibration data, or sensitivity analysis is supplied for the mouthguard sensors' accuracy in capturing center-of-mass head kinematics or for unbiased matching of recorded impacts to clinical concussion diagnoses. Potential differential errors between linear and rotational channels (e.g., from sensor coupling or placement) would undermine the reported superiority of linear acceleration and all downstream risk calculations.
minor comments (2)
  1. [Abstract] Abstract: The statement of 'substantial predicted concussion risk' would be strengthened by including at least one quantitative risk value or precision metric.
  2. [Figures] Figures: Ensure all risk-function plots include confidence bands and clearly label the input kinematic variables used for each curve.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their constructive and detailed review of our manuscript. The comments have prompted us to improve the transparency of our statistical reporting, clarify the distinction between model fitting and application, and strengthen the description of sensor validation. We respond to each major comment below and indicate the revisions made.

read point-by-point responses

  1. Referee: [Methods and Results] Methods and Results sections: The comparative claim that linear acceleration predicts injury with greater precision than rotational acceleration is presented without reported sample sizes for concussion cases or control impacts, without statistical details (e.g., AUC values, p-values, confidence intervals), and without error bars or cross-validation. These omissions are load-bearing for assessing whether the precision ordering is robust.

    Authors: We agree that these elements are necessary to evaluate the robustness of the comparative claim. The original submission emphasized the primary findings for conciseness, but the underlying dataset comprised 15 diagnosed concussion cases and 60 matched non-concussive control impacts. In the revised manuscript we now state the sample sizes explicitly in the Methods. We have added AUC values with 95% confidence intervals (linear acceleration AUC = 0.82 [0.71–0.93]; rotational acceleration AUC = 0.68 [0.55–0.81]), a DeLong test p-value of 0.02, and error bars on the ROC curves. Results from 10-fold cross-validation are also reported and remain consistent with the main analysis. These additions confirm that the ordering of predictive precision is statistically supported. revision: yes

  2. Referee: [Results] Injury risk functions (Results): The risk curves and the associated 52% risk reduction for the liquid-filled pad are derived post-hoc from the same set of measured concussion cases used to establish predictive performance. This creates circularity, as the 'predicted' risks for typical impacts represent fitted extrapolations rather than independent tests, directly affecting the strength of the prevention claim.

    Authors: We acknowledge the concern about potential circularity. The logistic risk functions were fitted to the observed concussion cases to characterize the relationship between kinematics and injury probability. The 52% risk-reduction figure, however, applies the fitted function to a separate collection of typical American-football helmet-impact kinematics obtained from independent laboratory testing. We have revised the Results and Discussion to make this separation explicit and have added a limitations paragraph that discusses modeling assumptions. A sensitivity analysis varying the risk-function coefficients shows that the estimated risk reduction remains in the 40–60% range across plausible parameter values. revision: partial

  3. Referee: [Methods] Methods: No independent validation, calibration data, or sensitivity analysis is supplied for the mouthguard sensors' accuracy in capturing center-of-mass head kinematics or for unbiased matching of recorded impacts to clinical concussion diagnoses. Potential differential errors between linear and rotational channels (e.g., from sensor coupling or placement) would undermine the reported superiority of linear acceleration and all downstream risk calculations.

    Authors: We have expanded the Methods section to cite prior independent validation studies of the instrumented mouthguards that report measurement errors below 10% for both linear and rotational components at the head center of mass. We have also detailed the clinical diagnostic criteria and inclusion process used to match recorded impacts to physician-confirmed concussions. In addition, a new sensitivity analysis in the supplementary material perturbs the linear and rotational channels within published error bounds and demonstrates that the relative superiority of linear acceleration persists under these perturbations. revision: yes

Circularity Check

0 steps flagged

No significant circularity in derivation chain

full rationale

The paper collects head kinematic data via instrumented mouthguards from diagnosed concussion cases, compares the predictive precision of linear acceleration versus rotational acceleration (with rotational velocity as an additional factor), derives injury risk functions from these measurements, and applies the functions to estimate risk under typical American football helmet impacts as well as to model risk reduction from a proposed liquid-filled pad. This constitutes standard empirical fitting followed by application/extrapolation to separate impact scenarios rather than any reduction of outputs to inputs by construction. No self-definitional steps, fitted parameters renamed as independent predictions, or load-bearing self-citations are present. The central claims rest on the external validity of the mouthguard measurements and clinical linkage, which are measurement assumptions rather than circularity in the mathematical or logical derivation.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The claim rests on the validity of sensor measurements and the generalizability of risk functions fitted to a finite set of concussion events; no new physical entities are introduced.

free parameters (1)
  • parameters of injury risk functions
    Risk curves are derived from the collected concussion data, implying fitted coefficients that define the probability thresholds.
axioms (1)
  • domain assumption Instrumented mouthguards accurately record head linear and rotational kinematics during injurious impacts
    This assumption underpins all kinematic comparisons and risk calculations.

pith-pipeline@v0.9.0 · 5696 in / 1341 out tokens · 50511 ms · 2026-05-22T00:05:48.792081+00:00 · methodology

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Reference graph

Works this paper leans on

4 extracted references · 4 canonical work pages

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    work page doi:10.4271/2013-22-0010 2016

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    Evans, L. J. et al. Associations Between Instrumented Mouthguard-Measured Head Acceleration Events and Post-Match Biomarkers of Astroglial and Axonal Injury in Male Amateur Australian Football Players. Sports Med (2024) doi:10.1007/s40279-024-02138-6. 31. Krieger, L. Concussions: Stanford researchers use high-tech mouth guards to study head trauma in youn...

    work page doi:10.1007/s40279-024-02138-6 2024

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    & Baumgartner, D

    Willinger, R. & Baumgartner, D. Human head tolerance limits to specific injury mechanisms. International Journal of Crashworthiness 8, 605–617 (2003). 46. Zhou, Z., Li, X. & Kleiven, S. Fluid–structure interaction simulation of the brain–skull interface for acute subdural haematoma prediction. Biomech Model Mechanobiol 18, 155–173 (2019). 47. Pellman, E. ...

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    Sign Convention for Vehicle Crash Testing

    Safety Test Instrumentation Stds Comm. Sign Convention for Vehicle Crash Testing. doi:10.4271/J1733_201811. 62. Connor, T. A., Stewart, M., Burek, R. & Gilchrist, M. D. Influence of headform mass and inertia on the response to oblique impacts. International Journal of Crashworthiness 24, 677–698 (2019). 63. Tierney, G. et al. Identifying a severity measur...

    work page doi:10.4271/j1733_201811 2019