The Influence of Cervical Muscle Characteristics on Head Impact Biomechanics in Football

Background: An athlete is thought to reduce head acceleration after impact by contracting the cervical musculature, which increases the effective mass of the head. Purpose: To compare the odds of sustaining higher magnitude in-season head impacts between athletes with higher and lower preseason performance on cervical muscle characteristics. Study Design: Cohort study; Level of evidence, 2. Methods: Forty-nine high school and collegiate American football players completed a preseason cervical testing protocol that included measures of cervical isometric strength, muscle size, and response to cervical perturbation. Head impact biomechanics were captured for each player using the Head Impact Telemetry System. A median split was used to categorize players as either high or low performers for each of the following outcome measures: isometric strength (peak torque, rate of torque development), muscle size (cross-sectional area), and response to cervical perturbation (stiffness, angular displacement, muscle onset latency). The odds of sustaining moderate and severe head impacts were computed against the reference odds of sustaining mild head impacts across cervical characteristic categorizations. Results: Linemen with stronger lateral flexors and composite cervical strength had about 1.75 times’ increased odds of sustaining moderate linear head impacts rather than mild impacts compared with weaker linemen. Players who developed extensor torque more quickly had 2 times the increased odds of sustaining severe linear head impacts (odds ratio [OR], 2.10; 95% CI, 1.08-4.05) rather than mild head impacts. However, players with greater cervical stiffness had reduced odds of sustaining both moderate (OR, 0.77; 95% CI, 0.61-0.96) and severe (OR, 0.64; 95% CI, 0.46-0.89) head impacts compared with players with less cervical stiffness. Conclusion: The study findings showed that greater cervical stiffness and less angular displacement after perturbation reduced the odds of sustaining higher magnitude head impacts; however, the findings did not show that players with stronger and larger neck muscles mitigate head impact severity.